Contribution of Low Clouds to Global Warming Still Controversial

A slew of research papers over the last year have attributed the so far unexplained surge in recent global warming to a decline in low cloud cover. But such a connection is still controversial. Several of the papers question their own conclusions or employ dubious methodology.

Prominent among these publications is a 2025 study by a trio of German environmental scientists. From satellite data, the authors claim to have pinpointed record-low planetary albedo, caused by a reduction in low clouds, as the primary source of the recent global temperature surge. The lowered albedo is most prominent in northern mid-latitudes and the tropics.

Albedo is a measure of the earth’s ability to reflect incoming solar radiation. Melting of light-colored snow and sea ice due to warming exposes darker surfaces such as soil, rock and seawater, which have lower albedo. The less reflective surfaces absorb more of the sun’s radiation and thus push temperatures higher.

The same effect occurs with low-level clouds, which are the majority of the planet’s cloud cover. Low-level clouds such as cumulus and stratus clouds are thick enough to reflect 30-60% of the sun’s radiation that strikes them back into space, so they act like a parasol and normally cool the earth’s surface. But less cloud cover lowers albedo and therefore results in warming.

The figure below shows global total and low cloud cover since 2000, calculated by the study authors from two separate sets of satellite data, indicated by the red and black curves, respectively. The decline in low cloud cover is as much as 1.5% – small, but large enough to raise global temperatures by 0.22 degrees Celsius (0.40 degrees Fahrenheit), say the scientists.

Furthermore, the disappearance of low clouds due to global warming sets up a positive feedback loop since fewer clouds cause more warming, which in turn lowers cloud cover even more. Nevertheless, the study authors cast doubt on their conclusions by pointing out that it is difficult to disentangle low cloud feedback from internal variability of the climate system and indirect aerosol effects. Long-term natural variability is associated with ocean cycles such as the AMO (Atlantic Multidecadal Oscillation).

As I discussed in a 2024 post, a major reduction in emissions of SO₂ (sulfur dioxide) since 2020, arising from a ban on the use of high-sulfur fuels by ships, can boost global warming. SO₂ reacts with water vapor in the air to produce sulfate aerosol particles that linger in the atmosphere and reflect incoming sunlight; they also act as condensation nuclei for the formation of reflective clouds. So the reduction in shipping emissions also contributes to the decline in low cloud cover.

More data linking the decline in low cloud cover to global warming is depicted in the next figure, showing cloud cover calculated from a different set of satellite data, and temperatures in degrees Celsius relative to the mean tropospheric temperature from 1991 to 2020.

A second 2025 paper, by two Chinese environmental engineers and a U.S. scientist, maintains that tropical low cloud feedback is positive rather than negative and 71% stronger than previously thought. Their conclusion depends on use of an obscure mathematical technique known as Pareto optimization, to reconcile large positive cloud feedback for the Atlantic Ocean in some global climate models with negative feedback for the Pacific in other models.

However, these authors concede that if warming is more uniform between cold stratocumulus regions and warm cloud ascent areas than they have assumed, then tropical low cloud feedback is likely to be much lower or even negative.

In a 2023 post, I reported on empirical observations, made by a team of French and German scientists, that refute the notion of positive low cloud feedback and show that the mechanism causing the strongest cloud reductions due to warming in climate models doesn’t actually occur in nature. Their conclusions were based on collection and analysis of observational data from cumulus clouds near the Atlantic island of Barbados.

In climate models, the refuted mechanism leads to strong positive cloud feedback that amplifies global warming. The models find that low clouds would thin out, and many would not form at all, in a hotter world. But the research team’s analysis reveals that climate models with large positive feedbacks are implausible.

Weaker than expected low cloud feedback is also suggested by lack of the so-called CO2 “hot spot” in the atmosphere, as I discussed in a 2021 post. Climate models predict that the warming rate at altitudes of 9 to 12 km (6 to 7 miles) above the tropics should be about twice as large as at ground level. Yet the hot spot doesn’t show up in measurements made by weather balloons or satellites.

Next: Update: No Grand Solar Minimum Likely Anytime Soon

How Much Will Reduction in Shipping Emissions Stoke Global Warming?

A controversial new research paper claims that a major reduction in emissions of SO₂ (sulfur dioxide) since 2020, due to a ban on the use of high-sulfur fuels by ships, could result in additional global warming of 0.16 degrees Celsius (0.29 degrees Fahrenheit) for seven years – over and above that from other sources. The paper was published by a team of NASA scientists.

This example of the law of unintended consequences, if correct, would boost warming from human CO₂, as well as that caused by water vapor in the stratosphere resulting from the massive underwater eruption of the Hunga Tonga–Hunga Haʻapai volcano in 2022. The eruption, as I described in a previous post, is likely to raise global temperatures by 0.035 degrees Celsius (0.063 degrees Fahrenheit) during the next few years.

It’s been known for some time that SO₂, including that emanating from ship engines, reacts with water vapor in the air to produce aerosols. Sulfate aerosol particles linger in the atmosphere, reflecting incoming sunlight and also acting as condensation nuclei for the formation of reflective clouds. Both effects cause global cooling.

In fact, it was the incorporation of sulfate aerosols into climate models that enabled the models to successfully reproduce the cooling observed between 1945 and about 1975, a feature that had previously eluded modelers.   

On January 1, 2020, new IMO (International Maritime Organization) regulations lowered the maximum allowable sulfur content in international shipping fuels to 0.5%, a significant reduction from the previous 3.5%. This air pollution control measure has reduced cloud formation and the associated reflection of shortwave solar radiation, both reductions having inadvertently increased global warming.

As would be expected, the strongest effects show up in the world’s most traveled shipping lanes: the North Atlantic, the Caribbean and the South China Sea. The figure on the left below depicts the researchers’ calculated contribution from reduced cloud fraction to additional radiative forcing resulting from the SO₂ reduction. The figure on the right shows by how much the concentration of condensation nuclei in low maritime clouds has fallen since the regulations took effect.

The cloud fraction contribution is 0.11 watts per square meter. The other contributions, from a reduction in cloud water content and the drop in reflection of solar radiation, add up to a total of 0.2 watts per square meter extra radiative forcing averaged over the global ocean, arising from the new shipping regulations, the NASA scientists say.

The effect is concentrated in the Northern Hemisphere since there is relatively little shipping traffic in the Southern Hemisphere. The researchers calculate the boost to radiative forcing to be 0.32 watts per square meter in the Northern Hemisphere, but only 0.1 watts per square meter in the Southern Hemisphere. The hemispheric difference in their calculations of absorbed shortwave solar radiation (near the earth’s surface) can be seen in the following figure, to the right of the dotted line.

According to the paper, the additional radiative forcing of 0.2 watts per square meter since 2020 corresponds to added global warming of 0.16 degrees Celsius (0.29 degrees Fahrenheit) over seven years. Such an increase implies a warming rate of 0.24 degrees Celsius (0.43 degrees Fahrenheit) per decade from reduced SO₂ emissions alone, which is more than double the average warming rate since 1880 and 20% higher than the mean warming rate since 1980 of approximately 0.19 degrees Celsius (0.34 degrees Fahrenheit) per decade.

The researchers remark that the forcing increase of 0.2 watts per square meter is a staggering 80% of the measured gain in forcing from other sources since 2020, the net planetary heat uptake since then being 0.25 watts per square meter.

However, these controversial claims have been heavily criticized, and not just by climate change skeptics. Climate scientist and modeler Zeke Hausfather points out that total warming will be less than the estimated 0.16 degrees Celsius (0.29 degrees Fahrenheit), because the new shipping regulations have only a minimal effect on land, which covers 29% of the earth’s surface.

And, states Hausfather, the researchers’ energy balance model “does not reflect real-world heat uptake by the ocean, and no actual climate model has equilibration times anywhere near that fast.” Hausfather’s own 2023 estimate of additional warming due to the use of low-sulfur shipping fuels was a modest 0.045 degrees Celsius (0.081 degrees Fahrenheit) after 30 years, as shown in the figure below.

Further criticism of the paper’s methodology comes from Laura Wilcox, associate professor at the National Centre for Atmospheric Science at the University of Reading. Wilcox told media that the paper makes some “very bold statements about temperature changes … which seem difficult to justify on the basis of the evidence.” She also has concerns about the mathematics of the researchers' calculations, including the possibility that the effect of sulfur emissions is double-counted.

Next: Philippines Court Ruling Deals Deathblow to Success of GMO Golden Rice

Unexpected Sea Level Fluctuations Due to Gravity, New Evidence Shows

Although the average global sea level is rising as the world warms, the rate of rise is far from uniform across the planet and, in some places, is negative – that is, the sea level is falling. Recent research has revealed the role that localized gravity plays in this surprising phenomenon.   

The researchers used gravity-sensing satellites to track how changes in water retention on land can cause unexpected fluctuations in sea levels. While 75% of the extra water in the world’s oceans comes from melting ice sheets and mountain glaciers, they say, the other 25% is due to variations in water storage in ice-free land regions. These include changes in dam water levels, water used in agriculture, and extraction of groundwater which either evaporates or flows into the sea via rivers.

Water is heavy but, the researchers point out, moves easily. Thus local changes in sea level aren't just due to melting ice sheets or glaciers, but also reflect changes in the mass of water on nearby land. For example, the land gets heavier during large floods, which boosts its gravity and causes a temporary rise in local sea level. The opposite occurs during droughts or groundwater extraction, when the land becomes lighter, gravity falls and the local sea level drops.

A similar exchange of water explains why the sea level around Antarctica falls as the massive Antarctic ice sheet melts. The total mass of ice in the sheet is a whopping 24 million gigatonnes (26 million gigatons), enough to exert a significant gravitational pull on the surrounding ocean, making the sea level higher than it would be with no ice sheet. But as the ice sheet melts, this gravitational pull weakens and so the local sea level falls.

At the same time, however, distant sea levels rise in compensation. They also rise continuously over the long term because of the thermal expansion of seawater as it warms; added meltwater from both the Antarctic and Greenland ice sheets; and land subsidence caused by groundwater extraction, resulting from rapid urbanization and population growth. In an earlier post, I discussed how sea levels are affected by land subsidence.

The research also reveals how the pumping of groundwater in ice-free places, such as Mumbai in India and Taipei in Taiwan, can almost mask the sea level rise expected from distant ice sheet melting. Conversely, at Charleston on the U.S. Atlantic coast, where groundwater extraction is minimal, sea level rise appears to be accelerated.

All these and other factors contribute to substantial regional variation in sea levels across the globe. This is depicted in the following figure which shows the average rate of sea level rise, measured by satellite, between 1993 and 2014.

Clearly visible is the falling sea level in the Southern Ocean near Antarctica, as well as elevated rates of rise in the western Pacific and the east coast of North America. Note, however, that the figure is only for the period between 1993 and 2014. Over longer time scales, the global average rate of rise fluctuates considerably, most likely due to the gravitational effects of the giant planets Jupiter and Saturn.

Yet another gravitational influence on sea levels is La Niña, the cool phase of the ENSO (El Niño – Southern Oscillation) ocean cycle. The arrival of La Niña often brings torrential rain and catastrophic flooding to the Pacific northwest of the U.S., northern South America and eastern Australia. As mentioned before, the flooding temporarily enhances the gravitational pull of the land. This raises local sea levels, resulting in a lowering of more distant sea levels – the opposite of the effects from the melting Antarctic ice sheet or from groundwater extraction.

The influence of La Niña is illustrated in the figure below, showing the rate of sea level rise during the two most recent strong La Niñas, in 2010-12 and 2020-23. (Note that the colors in the sea level trend are reversed compared to the previous figure.) A significant local increase in sea level can be seen around both northern South America and eastern Australia, while the global level fell, especially in the 2010-12 La Niña event. Consecutive La Niñas in those years dumped so much rain on land that the average sea level worldwide fell about 5 mm (0.2 inches).

The current rate of sea level rise is estimated at 3.4 mm per year. Of this, the researchers calculate that over-extraction of groundwater alone contributes approximately 1 mm per year – meaning that the true rate of rise, predominantly from ice sheet melting and thermal expansion, is about 2.4 mm per year. Strong La Niñas lower this rate even more temporarily.

But paradoxically, as discussed above, groundwater extraction is causing local sea levels to fall. It’s local sea levels that matter to coastal communities and their engineers and planners.

Next: No Convincing Evidence That Extreme Wildfires Are Increasing

Shrinking Cloud Cover: Cause or Effect of Global Warming?

Clouds play a dominant role in regulating our climate. Observational data show that the earth’s cloud cover has been slowly decreasing since at least 1982, at the same time that its surface temperature has risen about 0.8 degrees Celsius (1.4 degrees Fahrenheit). Has the reduction in cloudiness caused that warming, as some heretical research suggests, or is it an effect of increased temperatures?

It's certainly true that clouds exert a cooling effect, as you’d expect – at least low-level clouds, which are the majority of the planet’s cloud cover. Low-level clouds such as cumulus and stratus clouds are thick enough to reflect 30-60% of the sun’s radiation that strikes them back into space, so they act like a parasol and cool the earth’s surface. Less cloud cover would therefore be expected to result in warming.

Satellite measurements of global cloud cover from 1982 to 2018 or 2019 are presented in the following two, slightly different figures, which also include atmospheric temperature data for the same period. The first figure shows cloud cover from one set of satellite data, and temperatures in degrees Celsius relative to the mean tropospheric temperature from 1991 to 2020.

The second figure shows cloud cover from a different set of satellite data, and absolute temperatures in degrees Fahrenheit. The temperature data were not measured directly but derived from measurements of outgoing longwave radiation, which is probably why the temperature range from 1982 to 2018 appears much larger than in the previous figure.

This second figure is the basis for the authors’ claim that 90% of global warming since 1982 is a result of fewer clouds. As can be seen, their estimated trendline temperature (red dotted line, which needs extending slightly) at the end of the observation period in 2018 was 59.6 degrees Fahrenheit. The reduction in clouds (blue dotted line) over the same interval was 2.7% - although the researchers erroneously conflate the cloud cover and temperature scales to come up with a 4.1% reduction.

Multiplying 59.6 degrees Fahrenheit by 2.7% yields a temperature change of 1.6 degrees Fahrenheit. The researchers then make use of the well-established fact that the Northern Hemisphere is up to 1.5 degrees Celsius (2.7 degrees Fahrenheit) warmer than the Southern Hemisphere. So, they say, clouds can account for (1.6/2.7) = 59% of the temperature difference between the hemispheres.

This suggests that clouds may be responsible for 59% of recent global warming, if the temperature difference between the two hemispheres is due entirely to the difference in cloud cover from hemisphere to hemisphere.

Nevertheless, this argument is on very weak ground. First, the authors wrongly used 4.1% instead of 2.7% as just mentioned, which incorrectly leads to a temperature change due to cloud reduction of 2.4 degrees Fahrenheit and an estimated contribution to global warming of a higher (2.4/2.7) = 89%, as they claim in their paper.

Regardless of this mistake, however, a temperature increase of even 1.6 degrees Fahrenheit is more than twice as large as the observed rise measured by the more reliable satellite data in the first figure above. And attributing the 1.5 degrees Celsius (2.7 degrees Fahrenheit) temperature difference between the two hemispheres entirely to cloud cover difference is dubious.

There is indeed a difference in cloud cover between the hemispheres. The Southern Hemisphere contains more clouds (69% average cloud cover) than the Northern Hemisphere (64%), partly because there is more ocean surface in the Southern Hemisphere, and thus more evaporation as the planet warms. This in itself would not explain why the Northern Hemisphere is warmer, however.

Southern Hemisphere clouds are also more reflective than their Northern Hemisphere counterparts. That is because they contain more liquid water droplets and less ice; it has been found that lack of ice nuclei causes low-level clouds to form less often. But apart from the ice content, the chemistry and dynamics of cloud formation are complex and depend on many factors. So associating the hemispheric temperature difference only with cloud cover is most likely invalid.

A few other research papers also claim that the falloff in cloud cover explains recent global warming, but their arguments are equally shaky. As is the proposal by joint winner of the 2022 Nobel Prize in Physics, John Clauser, of a cloud thermostat mechanism that controls the earth’s temperature: if cloud cover falls and the temperature climbs, the thermostat acts to create more clouds and cool the earth down again. Obviously, this has not happened.

Finally, it’s interesting to note that the current decline in cloud cover is not uniform across the globe. This can be seen in the figure below, which shows an expanding trend with time in coverage over the oceans, but a diminishing trend over land.

The expanding ocean cloud cover comes from increased evaporation of seawater with rising temperatures. The opposite trend over land is a consequence of the drying out of the land surface; evidently, the land trend dominates globally.

Next: Was the Permian Extinction Caused by Global Warming or CO2 Starvation?

El Niño and La Niña May Have Their Origins on the Sea Floor

One of the least understood aspects of our climate is the ENSO (El Niño – Southern Oscillation) ocean cycle, whose familiar El Niño (warm) and La Niña (cool) events cause drastic fluctuations in global temperature, along with often catastrophic weather in tropical regions of the Pacific and delayed effects elsewhere. A recent research paper attributes the phenomenon to tectonic and seismic activity under the oceans.

Principal author Valentina Zharkova, formerly at the UK’s Northumbria University, is a prolific researcher into natural sources of global warming, such as the sun’s internal magnetic field and the effect of solar activity on the earth’s ozone layer. Most of her studies involve sophisticated mathematical analysis and her latest paper is no exception.

Zharkova and her coauthor Irina Vasilieva make use of a technique known as wavelet analysis, combined with correlation analysis, to identify key time periods in the ONI (Oceanic Niño Index). The index, which measures the strength of El Niño and La Niña events, is the 3-monthly average difference from the long-term average sea surface temperature in the ENSO region of the tropical Pacific. Shown in the figure below are values of the index from 1950 to 2016.

Wavelet analysis supplies information both on which frequencies are present in a time series signal, and on when those frequencies occur, unlike a Fourier transform which decomposes a signal only into its frequency components.

Using the wavelet approach, Zharkova and Vasilieva have identified two separate ENSO cycles: one with a shorter period of 4-5 years, and a longer one with a period of 12 years. This is illustrated in the next figure which shows the ONI at top left; the wavelet spectrum of the index at bottom left, with the wavelet “power” indicated by the colored bar at top right; and the global wavelet spectrum at bottom right. 

The authors link the 4- to 5-year ENSO cycle to the motion of tectonic plates, a connection that has been made by other researchers. The 12-year ENSO cycle identified by their wavelet analysis they attribute to underwater volcanic activity; it does not correspond to any solar cycle or other known natural source of warming.

The following figure depicts an index (in red, right-hand scale), calculated by the authors, that measures the total annual volcanic strength and duration of all submarine volcanic eruptions from 1950 to 2023, superimposed on the ONI (in black) over the same period. A weak correlation can be seen between the ENSO ONI and undersea volcanic activity, the correlation being strongest at 12-year intervals.

Zharkova and Vasilieva estimate the 12-year ENSO correlation coefficient at 25%, a connection they label as “rather significant.” As I discussed in a recent post, retired physical geographer Arthur Viterito has proposed that submarine volcanic activity is the principal driver of global warming, via a strengthening of the thermohaline circulation that redistributes seawater and heat around the globe.

Zharkova and Vasilieva, however, link the volcanic eruptions causing the 12-year boost in the ENSO index to tidal gravitational forces on the earth from the giant planet Jupiter and from the sun. Jupiter of course orbits the sun and spins on an axis, just like Earth. But the sun is not motionless either: it too rotates on an axis and, because it’s tugged by the gravitational pull of the Jupiter and Saturn giants, orbits in a small but complex spiral around the center of the solar system.

Jupiter was selected by the researchers because its orbital period is 12 years - the same as the longer ENSO cycle identified by their wavelet analysis.

That Jupiter’s gravitational pull on Earth influences volcanic activity is clear from the next figure, in which the frequency of all terrestrial volcanic eruptions (underwater and surface) is plotted against the distance of Earth from Jupiter; the distance is measured in AU (astronomical units), where 1 AU is the average earth-sun distance. The thick blue line is for all eruptions, while the thick yellow line shows the eruption frequency in just the ENSO region.

What stands out is the increased volcanic frequency when Jupiter is at one of two different distances from Earth: 4.5 AU and 6 AU. The distance of 4.5 AU is Jupiter’s closest approach to Earth, while 6 AU is Jupiter’s distance when the sun is closest to Earth and located between Earth and Jupiter. The correlation coefficient between the 12-year ENSO cycle and the Earth-Jupiter distance is 12%.  

For the gravitational pull of the sun, Zharkova and Vasilieva find there is a 15% correlation between the 12-year ENSO cycle and the Earth-sun distance in January, when Earth’s southern hemisphere (where ENSO occurs) is closest to the sun. Although these solar system correlations are weak, Zharkova and Vasilieva say they are high considering the vast distances involved.

Next: Shrinking Cloud Cover: Cause or Effect of Global Warming?

Sea Ice Update: Arctic Stable, Antarctic Recovering

The climate doomsday machine constantly insists that sea ice at the two poles is shrinking inexorably and that the Arctic will soon be ice-free in the summer. But the latest data puts the kibosh on those predictions. The maximum winter Arctic ice extent last month was no different from 2023, and the minimum summer 2024 extent in the Antarctic, although lower than the long-term average, was higher than last year.

Satellite images of Arctic sea ice extent in February 2024, one month before its winter peak (left image), and Antarctic extent at its summer minimum the same month (right image), are shown in the figure below. Sea ice shrinks during summer months and expands to its maximum extent during the winter. The red lines in the figure denote the median ice extent from 1981 to 2010.

Arctic summer ice extent decreased by approximately 39% over the interval from 1979 to 2023, but was essentially the same in 2023 as it was in 2007. Arctic winter ice extent on March 3, 2024 was 11% lower than in 1979, when satellite measurements began, but slightly higher than in 2023, as indicated by the inset in the figure below.

Arctic winter maximum extent fluctuates less than its summer minimum extent, as can be seen in the right panel of the figure which compares the annual trend by month for various intervals during the satellite era, as well as for the low-summer-ice years of 2007 and 2012. The left panel shows the annual trend by month for all years from 2013 through 2024.

What is noticeable about this year’s winter maximum is that it was not unduly low, despite the Arctic being warmer than usual. According to the U.S. NSIDC (National Snow & Ice Data Center), February air temperatures in the Arctic troposphere, about 760 meters (2,500 feet) above sea level, were up to 10 degrees Celsius (18 degrees Fahrenheit) above average.

The NSIDC attributes the unusual warmth to a strong pressure gradient that forced relatively warm air over western Eurasia to flow into the Arctic. However, other explanations have been put forward for enhanced winter warming, such as the formation during non-summer seasons of more low-level clouds due to the increased area of open water compared to sea ice. The next figure illustrates this effect between 2008 and 2022.

Despite the long-term loss of ice in the Arctic, the sea ice around Antarctica had been expanding steadily during the satellite era up until 2016, growing at an average rate between 1% and 2% per decade, with considerable fluctuations from year to year. But it took a tumble in 2017, as depicted in the figure below.

Note that this figure shows “anomalies,” or departures from the February mean ice extent for the period from 1981 to 2010, rather than the minimum extent of summer ice in square km. The anomaly trend is plotted as the percent difference between the February extent for that year and the February mean from 1981 to 2010.

As can be seen, the summer ice minimum recovered briefly in 2020 and 2021, only to fall once more and pick up again this year. The left panel in the next figure shows the annual Antarctic trend by month for all years from 2013 through 2024, along with the summer minimum (in square km) in the inset. As for the Arctic previously, the right panel compares the annual trend by month for various intervals during the satellite era, as well as for the high-summer-ice years of 2012 and 2014.

Antarctic sea ice at its summer minimum this year was especially low in the Ross, Amundsen, and Bellingshausen Seas, all of which are on the West Antarctica coast, while the ice cover in the Weddell Sea to the north and along the East Antarctic coast was at average levels. Such a pattern is thought to be associated with the current El Niño.

A slightly different representation of the Antarctic sea ice trend is presented in the following figure, in which the February anomaly is shown directly in square km rather than as a difference percentage. This representation illustrates more clearly how the decline in summer sea ice extent has now persisted for seven years.

The overall trend from 1979 to 2023 is an insignificant 0.1% per decade relative to the 1981 to 2010 mean. Yet a prolonged increase above the mean occurred from 2008 to 2017, followed by the seven-year decline since then. The current downward trend has sparked debate and several possible reasons have been advanced, not all of which are linked to global warming. One analysis attributes the big losses of sea ice in 2017 and 2023 to extra strong El Niños.

Next: The Deceptive Catastrophizing of Weather Extremes: (1) The Science

Challenges to the CO2 Global Warming Hypothesis: (11) Global Warming Driven by Oceanic Seismic Activity, Not CO2

Although undersea volcanic eruptions can’t cause global warming directly, as I discussed in a previous post, they can contribute indirectly by altering the deep-ocean thermohaline circulation. According to a recent lecture, submarine volcanic activity is currently intensifying the thermohaline circulation sufficiently to be the principal driver of global warming.

The lecture was delivered by Arthur Viterito, a renowned physical geographer and retired professor at the College of Southern Maryland. His provocative hypothesis links an upsurge in seismic activity at mid-ocean ridges to recent global warming, via a strengthening of the ocean conveyor belt that redistributes seawater and heat around the globe.

Viterito’s starting point is the observation that satellite measurements of global warming since 1979 show distinct step increases following major El Niño events in 1997-98 and 2014-16, as demonstrated in the following figure. The figure depicts the satellite-based global temperature of the lower atmosphere in degrees Celsius, as compiled by scientists at the University of Alabama in Huntsville; temperatures are annual averages and the zero baseline represents the mean tropospheric temperature from 1991 to 2020.

Viterito links these apparent jumps in warming to geothermal heat emitted by volcanoes and hydrothermal vents in the middle of the world’s ocean basins – heat that shows similar step increases over the same time period, as measured by seismic activity. The submarine volcanoes and hydrothermal vents lie along the earth’s mid-ocean ridges, which divide the major oceans roughly in half and are illustrated in the next figure. The different colors denote the geothermal heat output (in milliwatts per square meter), which is highest along the ridges.

The total mid-ocean seismic activity along the ridges is shown in the figure below, in which the global tropospheric temperature, graphed in the first figure above, is plotted in blue against the annual number of mid-ocean earthquakes (EQ) in orange. The best fit between the two sets of data occurs when the temperature readings are lagged by two years: that is, the 1979 temperature reading is paired with the 1977 seismic reading, and so on. As already mentioned, seismic activity since 1979 shows step increases similar to the temperature.

A regression analysis yields a correlation coefficient of 0.74 between seismic activity and the two-year lagged temperatures, which implies that mid-ocean geothermal heat accounts for 55% of current global warming, says Viterito. However, a correlation coefficient of 0.74 is not as high as some estimates of the correlation between rising CO₂ and temperature.

In support of his hypothesis, Viterito states that multiple modeling studies have demonstrated how geothermal heating can significantly strengthen the thermohaline circulation, shown below. He then links the recently enhanced undersea seismic activity to global warming of the atmosphere by examining thermohaline heat transport to the North Atlantic-Arctic and western Pacific oceans.

In the Arctic, Viterito points to several phenomena that he believes are a direct result of a rapid intensification of North Atlantic currents which began around 1995 – the same year that mid-ocean seismic activity started to rise. The phenomena include the expansion of a phytoplankton bloom toward the North Pole due to incursion of North Atlantic currents into the Arctic; enhanced Arctic warming; a decline in Arctic sea ice; and rapid warming of the Subpolar Gyre, a circular current south of Greenland.

In the western Pacific, he cites the increase since 1993 in heat content of the Indo-Pacific Warm Pool near Indonesia; a deepening of the Indo-Pacific Warm Pool thermocline, which divides warmer surface water from cooler water below; strengthening of the Kuroshio Current near Japan; and recently enhanced El Niños.

But, while all these observations are accurate, they do not necessarily verify Viterito’s hypothesis that submarine earthquakes are driving current global warming. For instance, he cites as evidence the switch of the AMO (Atlantic Multidecadal Oscillation) to its positive or warm phase in 1995, when mid-ocean seismic activity began to increase. However, his assertion begs the question: Isn’t the present warm phase of the AMO just the same as the hundreds of warm cycles that preceded it?

In fact, perhaps the AMO warm phase has always been triggered by an upturn in mid-ocean earthquakes, and has nothing to do with global warming.

There are other weaknesses in Viterito’s argument too. One example is his association of the decline in Arctic sea ice, which also began around 1995, with the current warming surge. What he overlooks is that the sea ice extent stopped shrinking on average in 2007 or 2008, but warming has continued.

And while he dismisses CO₂ as a global warming driver because the rising CO₂ level doesn’t show the same step increases as the tropospheric temperature, a correlation coefficient between CO₂ and temperature as high as 0.8 means that any CO₂ contribution is not negligible.

It’s worth noting here that a strengthened thermohaline circulation is the exact opposite of the slowdown postulated by retired meteorologist William Kininmonth as the cause of global warming, a possibility I described in an earlier post in this Challenges series (#7). From an analysis of longwave radiation from greenhouse gases absorbed at the tropical surface, Kininmonth concluded that a slowdown in the thermohaline circulation is the only plausible explanation for warming of the tropical ocean.

Next: Foundations of Science Under Attack in U.S. K-12 Education

Rapid Climate Change Is Not Unique to the Present

Rapid climate change, such as the accelerated warming of the past 40 years, is not a new phenomenon. During the last ice age, which spanned the period from about 115,000 to 11,000 years ago, temperatures in Greenland rose abruptly and fell again at least 25 times. Corresponding temperature swings occurred in Antarctica too, although they were less pronounced than those in Greenland.

The striking but fleeting bursts of heat are known as Dansgaard–Oeschger (D-O) events, named after palaeoclimatologists Willi Dansgaard and Hans Oeschger who examined ice cores obtained by deep drilling the Greenland ice sheet. What they found was a series of rapid climate fluctuations, when the icebound earth suddenly warmed to near-interglacial conditions over just a few decades, only to gradually cool back down to frigid ice-age temperatures.

Ice-core data from Greenland and Antarctica are depicted in the figure below; two sets of measurements, recorded at different locations, are shown for each. The isotopic ratios of ¹⁸O to ¹⁶O, or δ¹⁸O, and ²H to ¹H, or δ²H, in the cores are used as proxies for the past surface temperature in Greenland and Antarctica, respectively.

Multiple D-O events can be seen in the four sets of data, stronger in Greenland than Antarctica. The periodicity of successive events averages 1,470 years, which has led to the suggestion of a 1,500-year cycle of climate change associated with the sun.

Somewhat similar cyclicity has been observed during the present interglacial period or Holocene, with eight sudden temperature drops and recoveries, mirroring D-O temperature spurts, as illustrated by the thick black line in the next figure. Note that the horizontal timescale runs forward, compared to backward in the previous (and following) figure.

These so-called Bond events were identified by geologist Gerard Bond and his colleagues, who used drift ice measured in deep-sea sediment cores, and δ¹⁸O as a temperature proxy, to study ancient climate change. The deep-sea cores contain glacial debris rafted into the oceans by icebergs, and then dropped onto the sea floor as the icebergs melted. The volume of glacial debris was largest, and it was carried farthest out to sea, when temperatures were lowest.

Another set of distinctive, abrupt events during the latter part of the last ice age were Heinrich events, which are related to both D-O events and Bond cycles. Five of the six or more Heinrich events are shown in the following figure, where the red line represents Greenland ice-core δ¹⁸O data, and some of the many D-O events are marked; the figure also includes Antarctic δ¹⁸O data, together with ice-age CO₂ and CH₄ levels.

As you can see, Heinrich events represent the cooling portion of certain D-O events. Although the origins of both are debated, they are thought likely to be associated with an increase in icebergs discharged from the massive Laurentide ice sheet which covered most of Canada and the northern U.S. Just as with Bond events, Heinrich and D-O events left a signature on the ocean floor, in this case in the form of large rocks eroded by glaciers and dropped by melting icebergs.

The melting icebergs would have also disgorged enormous quantities of freshwater into the Labrador Sea. One hypothesis is that this vast influx of freshwater disrupted the deep-ocean thermohaline circulation (shown below) by lowering ocean salinity, which in turn suppressed deepwater formation and reduced the thermohaline circulation.

Since the thermohaline circulation plays an important role in transporting heat northward, a slowdown would have caused the North Atlantic to cool, leading to a Heinrich event. Later, as the supply of freshwater decreased, ocean salinity and deepwater formation would have increased again, resulting in the rapid warming of a D-O event.

However, this is but one of several possible explanations. The proposed freshwater increase and reduced deepwater formation during D-O events could have resulted from changes in wind and rainfall patterns in the Northern Hemisphere, or the expansion of Arctic sea ice, rather than melting icebergs.

In 2021, an international team of climate researchers concluded that when certain parts of the ice-age climate system changed abruptly, other parts of the system followed like a series of dominoes toppling in succession. But to their surprise, neither the rate of change nor the order of the processes were the same from one event to the other.

Using data from two Greenland ice cores, the researchers discovered that changes in ocean currents, sea ice and wind patterns were so closely intertwined that they likely triggered and reinforced each other in bringing about the abrupt climate changes of D-O and Heinrich events.

While there’s clearly no connection between ice-age D-O events and today’s accelerated warming, this research and the very existence of such events show that the underlying causes of rapid climate change can be elusive.

Next: Challenges to the CO2 Global Warming Hypothesis: (11) Global Warming Is Driven by Oceanic Seismic Activity, Not CO2

Antarctica Sending Mixed Climate Messages

Antarctica, the earth’s coldest and least-populated continent, is an enigma when it comes to global warming.

While the huge Antarctic ice sheet is known to be shedding ice around its edges, it may be growing in East Antarctica. Antarctic sea ice, after expanding slightly for at least 37 years, took a tumble in 2017 and reached a record low in 2023. And recent Antarctic temperatures have swung from record highs to record lows. No one is sure what’s going on.

The influence of global warming on Antarctica’s temperatures is uncertain. A 2021 study concluded that both East Antarctica and West Antarctica have cooled since the beginning of the satellite era in 1979, at rates of 0.70 degrees Celsius (1.3 degrees Fahrenheit) per decade and 0.42 degrees Celsius (0.76 degrees Fahrenheit) per decade, respectively. But over the same period, the Antarctic Peninsula (on the left in the adjacent figure) has warmed at a rate of 0.18 degrees Celsius (0.32 degrees Fahrenheit) per decade.

During the southern summer, two locations in East Antarctica recorded record low temperatures early this year. At the Concordia weather station, located at the 4 o’clock position from the South Pole, the mercury dropped to -51.2 degrees Celsius (-60.2 degrees Fahrenheit) on January 31, 2023. This marked the lowest January temperature recorded anywhere in Antarctica since the first meteorological observations there in 1956.

Two days earlier on January 29, 2023, the nearby Vostok station, about 400 km (250) miles closer to the South Pole, registered a low temperature of -48.7 degrees Celsius (-55.7 degrees Fahrenheit), that location’s lowest January temperature since 1957. Vostok has the distinction of reporting the lowest temperature ever recorded in Antarctica, and also the world record low, of -89.2 degrees Celsius (-128.6 degrees Fahrenheit) on July 21, 1984.

Barely a year before, however, East Antarctica had experienced a heat wave, when the temperature soared to -10.1 degrees Celsius (13.8 degrees Fahrenheit) at the Concordia station on March 18, 2022. This balmy reading was the highest recorded hourly temperature at that weather station since its establishment in 1996, and 20 degrees Celsius (36 degrees Fahrenheit) above the previous March record high there. Remarkably, the temperature remained above the previous March record for three consecutive days, including nighttime.

Antarctic sea ice largely disappears during the southern summer and reaches its maximum extent in September, at the end of winter. The two figures below illustrate the winter maximum extent in 2023 (left) and the monthly variation of Antarctic sea ice extent this year from its March minimum to the September maximum (right).

The black curve on the right depicts the median extent from 1981 to 2010, while the dashed red and blue curves represent 2022 and 2023, respectively. It's clear that Antarctic sea ice in 2023 has lagged the median and even 2022 by a wide margin throughout the year. The decline in summer sea ice extent has now persisted for six years, as seen in the following figure which shows the average monthly extent since satellite measurements began, as an anomaly from the median value.

The overall trend from 1979 to 2023 is an insignificant 0.1% per decade relative to the 1981 to 2010 median. Yet a prolonged  increase above the median occurred from 2008 to 2017, followed by the six-year decline since then. The current downward trend has sparked much debate and several possible reasons have been put forward, not all of which are linked to global warming. One analysis attributes the big losses of sea ice in 2017 and 2023 to extra strong El Niños.

Melting of the Antarctic ice sheet is currently causing sea levels to rise by 0.4 mm (16 thousandths of an inch) per year, contributing about 10% of the global total. But the ice loss is not uniform across the continent, as seen in the next figure showing changes in Antarctic ice sheet mass since 2002.

In the image on the right, light blue shades indicate ice gain while orange and red shades indicate ice loss. White denotes areas where there has been very little or no change in ice mass since 2002; gray areas are floating ice shelves whose mass change is not measured by this satellite method.

You can see that East Antarctica has experienced modest amounts of ice gain, which is due to warming-enhanced snowfall. Nevertheless, this gain has been offset by significant loss of ice in West Antarctica over the same period, largely from melting of glaciers – which is partly caused by active volcanoes underneath the continent. While the ice sheet mass declined at a fairly constant rate of 133 gigatonnes (147 gigatons) per year from 2002 to 2020, it appears that the total mass may have reached a minimum and is now on the rise again.

Despite the hullabaloo about its melting ice sheet and shrinking sea ice, what happens next in Antarctica continues to be a scientific mystery.

Next: Two Statistical Studies Attempt to Cast Doubt on the CO2 Narrative

No Evidence That Today’s El Niños Are Any Stronger than in the Past

The current exceptionally strong El Niño has revived discussion of a question which comes up whenever the phenomenon recurs every two to seven years: are stronger El Niños caused by global warming? While recent El Niño events suggest that in fact they are, a look at the historical record shows that even stronger El Niños occurred in the distant past.

El Niño is the warm phase of ENSO (the El Niño – Southern Oscillation), a natural ocean cycle that causes drastic temperature fluctuations and other climatic effects in tropical regions of the Pacific. Its effect on atmospheric temperatures is illustrated in the figure below. Warm spikes such as those in 1997-98, 2009-10, 2014-16 and 2023 are due to El Niño; cool spikes like those in 1999-2001 and 2008-09 are due to the cooler La Niña phase.

A slightly different temperature record, of selected sea surface temperatures in the El Niño region of the Pacific, averaged yearly from 1901 to 2017, is shown in the next figure from a 2019 study.

Here the baseline is the mean sea surface temperature over the 1901-2017 interval, and the black dashed line at 0.6 degrees Celsius is defined by the study authors as the threshhold for an El Niño event. The different colors represent various regional types of El Niño; the gray bars mark warm years in which no El Niño developed.

This year’s gigantic spike in the tropospheric temperature to 0.93 degrees Celsius (1.6 degrees Fahrenheit) – a level that set alarm bells ringing – is clearly the strongest El Niño by far in the satellite record. Comparison of the above two figures shows that it is also the strongest since 1901. So it does indeed appear that El Niños are becoming stronger as the globe warms, especially since 1960.

Nevertheless, such a conclusion is ill-considered as there is evidence from an earlier study that strong El Niños have been plentiful in the earth’s past.

As I described in a previous post, a team of German paleontologists established a complete record of El Niño events going back 20,000 years, by examining marine sediment cores drilled off the coast of Peru. The cores contain an El Niño signature in the form of tiny, fine-grained stone fragments, washed into the sea by multiple Peruvian rivers following floods in the country caused by heavy El Niño rainfall.

The research team classified the flood signal as very strong when the concentration of stone fragments, known as lithics, was more than two standard deviations above the centennial mean. The frequency of these very strong events over the last 12,000 years is illustrated in the next figure; the black and gray bars show the frequency as the number of 500- and 1,000-year floods, respectively. Radiocarbon dating of the sediment cores was used to establish the timeline.

A more detailed record is presented in the following figure, showing the variation over 20,000 years of the sea surface temperature off Peru (top), the lithic concentration (bottom) and a proxy for lithic concentration (center). Sea surface temperatures were derived from chemical analysis of the marine sediment cores.

You can see that the lithic concentration and therefore El Niño strength were high around 2,000 and 10,000 years ago – approximately the same periods when the most devastating floods occurred. The figure also reveals the absence of strong El Niño activity from 5,500 to 7,500 years ago, a dry interval without any major Peruvian floods as reflected in the previous figure.

If you examine the lithic plots carefully, you can also see that the many strong El Niños approximately 2,000 and 10,000 years ago were several times stronger (note the logarithmic concentration scale) than current El Niños on the far left of the figure. Those two periods were warmer than today as well, being the Roman Warm Period and the Holocene Thermal Maximum, respectively.

So there is nothing remarkable about recent strong El Niños.

Despite this, the climate science community is still uncertain about the global warming question. The 2019 study described above found that since the 1970s, formation of El Niños has shifted from the eastern to the western Pacific, where ocean temperatures are higher. From this observation, the study authors concluded that future El Niños may intensify. However, they qualified their conclusion by stating that:

… the root causes of the observed background changes in the later part of the 20th century remain elusive … Natural variability may have added significant contributions to the recent warming.

Recently, an international team of 17 scientists has conducted a theoretical study of El Niños since 1901 using 43 climate models, most of which showed the same increase in El Niño strength since 1960 as the actual observations. But again, the researchers were unable to link this increase to global warming, declaring that:

Whether such changes are linked to anthropogenic warming, however, is largely unknown.

The researchers say that resolution of the question requires improved climate models and a better understanding of El Niño itself. Some climate models show El Niño becoming weaker in the future.

Next: Antarctica Sending Mixed Climate Messages

Estimates of Economic Losses from El Niños Are Far-fetched

A recent study makes the provocative claim that some of the most intense past El Niño events cost the global economy from $4 trillion to $6 trillion over the following years. That’s two orders of magnitude higher than previous estimates, but almost certainly wrong.

One reason for the enormous difference is that earlier estimates only examined the immediate economic toll, whereas the new study estimated cumulative losses over the five-year period after a warming El Niño. The study authors say, correctly, that the economic downturn triggered by this naturally occurring climate cycle can last that long.

However, even when this drawn-out effect is taken into account, the new study’s cost estimates are still one order of magnitude greater than other estimates in the scientific literature, such as those of the University of Colorado’s Roger Pielke Jr., who studies natural disasters. His estimated time series of total weather disaster losses as a proportion of global GDP from 1990 to 2020 is shown in the figure below.

The accounting used in the new study includes the “spatiotemporal heterogeneity of El Niño teleconnections,” teleconnections being links between weather phenomena at widely separated locations. Country-level teleconnections are based on correlations between temperature or rainfall in that country, and indexes commonly used to define El Niño and its cooling counterpart, La Niña. Teleconnections are strongest in the tropics and weaker in midlatitudes.

The researchers’ accounting procedure estimates total losses from the 1997-98 El Niño at a staggering $5.7 trillion by 2003, compared with a previous estimate of only $36 billion in the immediate aftermath of the event. For the earlier 1982-83 El Niño, the study estimates the total costs at $4.1 trillion by 1988. The calculated global distribution of GDP losses following both events is illustrated in the next figure.

To see how implausible these trillion-dollar estimates are, it’s only necessary to refer to Pielke’s graph above, which relies on official data from the insurance industry (including leading reinsurance company Munich Re) and the World Bank. His graph indicates that the peak loss from all 1998 weather disasters was 0.38% of global GDP for that year.

As El Niño was not the only disaster in 1998 – others include floods and hurricanes – this number represents an upper limit for instant El Niño losses. Using a value for global GDP in 1998 of $31,533 billion in current U.S. dollars, 0.38% was a maximum instant loss of $120 billion. Over a subsequent 5-year period, the maximum loss would have been 5 times as much, or $600 billion assuming the same annual loss each year which is undoubtedly an overestimate.

This inflated estimate of $600 billion is still an order of magnitude smaller than the study’s $5.7 trillion by 2003. In reality, the discrepancy is larger yet because the actual 5-year loss was likely much less than $600 billion as just discussed.

Two other observations about Pielke’s graph cast further doubt on the methodology of the researchers’ accounting procedure. First, the strongest El Niños in that 21-year period were those in 1997-98, 2009-10 and 2014-16. The graph does indeed show peaks in 1998-99 and in 2017, one year after a substantial El Niño – but not in 2011 following the 2009-10 event. This alone suggests that financial losses from El Niño are not as large as the researchers think.

Furthermore, there’s a strong peak in 2005, the largest in the 21 years of the graph, which doesn’t correspond to any substantial El Niño. The implication is that losses from other types of weather disaster can dominate losses from El Niño.

It’s important to get an accurate handle on economic losses from El Niño and other weather disasters, in case global warming exacerbates such events in the future – although, as I’ve written extensively, there’s no evidence to date that this is happening yet. Effects of El Niño include catastrophic flooding in the western Americas, flooding or episodic droughts in Australia, and coral bleaching.

The study authors stand by their research, however, estimating that the 2023 El Niño could hold back the global economy by $3 trillion over the next five years, a figure not included in their paper. But others are more skeptical. Climate economist Gary Yohe commented that “the enormous estimates cannot be explained simply by forward-looking accounting.” And Mike McPhaden, a senior scientist at NOAA (the U.S. National Oceanic and Atmospheric Administration) who was not involved in the research, called the study “provocative.”

Next: Targeting Farmers for Livestock Greenhouse Gas Emissions Is Misguided

Record Heat May Be from Natural Sources: El Niño and Water Vapor from 2022 Tonga Eruption

The record heat worldwide over the last few months – simultaneous heat waves in both the Northern and Southern Hemispheres, and abnormally warm oceans – has led to the hysterical declaration of “global boiling” by the UN Secretary General, the media and even some climate scientists. But a rational look at the data reveals that the cause may be natural sources, not human CO₂.

The primary source is undoubtedly the warming El Niño ocean cycle, a natural event that recurs at irregular intervals from two to seven years. The last strong El Niño, which temporarily raised global temperatures by about 0.14 degrees Celsius (0.25 degrees Fahrenheit), was in 2016. For comparison, it takes a full decade for current global warming to increase temperatures by that much. 

However, on top of the 2023 El Niño has been an unexpected natural source of warming – water vapor in the upper atmosphere, resulting from a massive underwater volcanic eruption in the South Pacific kingdom of Tonga in January 2022.

Normally, erupting volcanoes cause significant global cooling, from shielding of sunlight by sulfate aerosol particles in the eruption plume that linger in the atmosphere. Following the 1991 eruption of Mount Pinatubo in the Philippines, for example, the global average temperature fell by 0.6 degrees Celsius (1.1 degrees Fahrenheit) for more than a year.

But the eruption of the Hunga Tonga–Hunga Haʻapai volcano did more than just launch a destructive tsunami and shoot a plume of ash, gas, and pulverized rock 55 kilometers (34 miles) into the sky. It also injected 146 megatonnes (161 megatons) of water vapor into the stratosphere (the layer of the atmosphere above the troposphere) like a geyser. Because it occurred only about 150 meters (500 feet) underwater, the eruption immediately superheated the shallow seawater above and converted it explosively into steam.

Although the excess water vapor – enough to fill more than 58,000 Olympic-size swimming pools – was originally localized to the South Pacific, it quickly diffused over the whole globe. According to a recent study by a group of atmospheric physicists at the University of Oxford and elsewhere, the eruption boosted the water vapor content of the stratosphere worldwide by as much as 10% to 15%. 

Water vapor is a powerful greenhouse gas, the dominant greenhouse gas in the atmosphere in fact; it is responsible for about 70% of the earth’s natural greenhouse effect, which keeps the planet at a comfortable enough temperature for living organisms to survive, rather than 33 degrees Celsius (59 degrees Fahrenheit) cooler. So even 10–15% extra water vapor in the stratosphere makes the earth warmer.

The study authors estimated the additional warming from the Hunga Tonga eruption using a simple climate model combined with a widely available radiative transfer model. Their estimate was a maximum global warming of 0.035 degrees Celsius (0.063 degrees Fahrenheit) in the year following the eruption, diminishing over the next five years. The cooling effect of the small amount of sulfur dioxide (SO₂) from the eruption was found to be minimal.

As I explained in an earlier post, any increase in ocean surface temperatures from the Hunga Tonga eruption would have been imperceptible, at a minuscule 14 billionths of a degree Celsius or less. That’s because the oceans, which cover 71% of the earth’s surface, are vast and can hold 1,000 times more heat than the atmosphere. Undersea volcanic eruptions can, however, cause localized marine heat waves, as I discussed in another post.

Although 0.035 degrees Celsius (0.063 degrees Fahrenheit) of warming from the Hunga Tonga eruption pales in comparison with 2016’s El Niño boost of 0.14 degrees Celsius (0.25 degrees Fahrenheit), it’s nevertheless more than double the average yearly increase of 0.014 degrees Celsius (0.025 degrees Fahrenheit) of global warming from other sources such as greenhouse gases.

El Niño is the warm phase of ENSO (the El Niño – Southern Oscillation), a natural cycle that causes drastic temperature fluctuations and other climatic effects in tropical regions of the Pacific, as well as raising temperatures globally. Its effect on sea surface temperatures in the central Pacific is illustrated in the figure below. It can be seen that the strongest El Niños, such as those in 1998 and 2016, can make Pacific surface waters more than 2 degrees Celsius (3.6 degrees Fahrenheit) hotter for a whole year or so. 

Exactly how strong the present El Niño will be is unknown, but the heat waves of July suggest that this El Niño – augmented by the Hunga Tonga water vapor warming – may be super-strong. Satellite measurements showed that, in July 2023 alone, the temperature of the lower troposphere rose from 0.38 degrees Celsius (0.68 degrees Fahrenheit) to 0.64 degrees Celsius (1.2 degrees Fahrenheit) above the 1991-2020 mean.

If this El Niño turns out to be no stronger than in the past, then the source of the current “boiling” heat will remain a mystery. Perhaps the Hunga Tonga water vapor warming is larger than the Oxford group estimates. The source certainly isn’t any warming from human CO₂, which raises global temperatures gradually and not abruptly as we’ve seen in 2023.

Next: Has the Mainstream Media Suddenly Become Honest in Climate Reporting?

Are Ocean Surface Temperatures, Not CO2, the Climate Control Knob?

According to the climate change narrative, modern global warming is largely the result of human emissions of CO₂ into the atmosphere. But a recent lecture questioned that assertion with an important observation suggesting that ocean surface temperatures, not CO₂, are the planet’s climate control knob.

The lecture was delivered by Norwegian Ole Humlum, who was formerly a full professor in physical geography at both the University Centre in Svalbard, Norway and the University of Oslo, in addition to holding visiting positions in Scotland and the Faroe Islands. He currently publishes regular updates on the state of the global climate.

In his lecture, Humlum dwelt on temperature measurements of the world’s oceans. Since 2004, ocean temperatures have been studied in detail at depths of up to 2 km (1.2 miles), by means of a global array of almost 3,900 Argo profiling floats. These free-drifting robotic floats patrol the oceans, taking a deep dive every 10 days to probe the temperature and salinity of the watery depths, and transmitting the data to a satellite within hours of reaching the surface again. A 2018 map of the Argo array is shown below.

The next figure illustrates how the oceans have warmed during the period that the floats have been in operation, up to August 2020. The vertical scale is the global ocean temperature change in degrees Celsius averaged from 65^oS to 65^oN (excluding the polar regions), while the horizontal scale gives the depth up to 1,900 meters (6,200 feet).

You can see that warming has been most prominent at the surface, where the average sea surface temperature has gone up since 2004 by about 0.27 degrees Celsius (0.49 degrees Fahrenheit). The temperature increase deep down is an order of magnitude smaller. Most of the temperature rise at shallow depths comes from the tropics (30^oS to 30^oN) and the Antarctic (65^oS to 55^oS), although the Arctic (55^oN to 65^oN) measurements reveal considerable cooling down to about 1,400 meters (4,600 feet) in that region.

But Humlum’s most profound observation is of the timeline for Argo temperature measurements as a function of depth. These are depicted in the following figure showing global depth profiles for the tropical oceans in degrees Celsius, from 2004 to 2014. The tropics cover almost 40% of the earth’s surface; the oceans in total cover 71%.

The fluctuations in each Argo depth profile arise from seasonal variations in temperature from summer to winter, which are more pronounced at the surface than at greater depths. If you focus your attention on any yearly summer peak at zero depth, you will notice that it moves to the right – that is, to later times – as the depth increases. In other words, there is a time delay of any temperature change with depth.

From a correlation analysis of the Argo data, Humlum finds that the time delay at a depth of 200 meters (650 feet) is a substantial 20 months, so that it takes 20 months for a temperature increase or decrease at the tropical surface to propagate down to that depth. A similar, though smaller, delay exists between any change in sea surface temperature (SST) and corresponding temperature changes in the atmosphere and on land, as shown in the figure below.

At an altitude of 200 meters (650 feet) in the atmosphere, changes in the SST show up slightly less than half a month later. But in the lower troposphere, where satellite temperature measurements are made, the delay is 2 months, as it is also for land surface temperatures. Humlum’s crucial argument is that sea surface temperatures lead all other global temperature observations – that is, the global temperature signal originates at the ocean surface.

However, according to the CO₂ global warming hypothesis, the CO₂ signal originates at an altitude of about 9 km (5.6 miles) in the upper troposphere and is seen at the sea surface some time later. So the CO₂ hypothesis predicts that the sea surface is a lagging, not a leading indicator – exactly the opposite of what actual observations are telling us.

Humlum concludes that CO₂ cannot be the earth’s climate control knob and that our global climate is apparently controlled by the SST. The climate control knob must instead be whatever natural system controls sea surface temperatures. Potential candidates, he says, include the sun, cloud cover, sediments and organic life in the oceans, and the action of winds. Further research is needed to identify which of these possibilities truly powers the global climate.

Next: Mainstream Media Jumps on Extreme Weather Caused by Climate Change Bandwagon

New Research Finds Climate Models Unable to Reproduce Ocean Surface Temperatures

An earlier post of mine described how a group of prestigious U.S. climate scientists recently admitted that some climate models run too hot, greatly exaggerating future global warming. Now another group has published a research paper revealing that a whole ensemble of models is unable to reproduce observed sea surface temperature trends in the Pacific and Southern Oceans since 1979.

The observed trends include enhanced warming in the Indo-Pacific Warm Pool – a large body of water near Indonesia where sea surface temperatures exceed 28 degrees Celsius (82 degrees Fahrenheit) year-round – as well as slight cooling in the eastern equatorial Pacific, and cooling in the Southern Ocean.

Climate models predict exactly opposite effects in all three regions, as illustrated in the following figure. The top panel depicts the global trend in measured sea surface temperatures (SSTs) from 1979 to 2020, while the middle panel depicts the multimodel mean of hindcasted temperatures over the same period from a large 598-member ensemble, based on 16 different models and various possible CO₂ emissions scenarios ranging from low (SSP2-4.5) to high (RCP8.5) emissions. The bottom panel shows the difference.

You can see that the difference between observed and modeled temperatures is indeed marked. Considerable warming in the Indo-Pacific Warm Pool and the western Pacific, together with cooling in the eastern Pacific and Southern Ocean, are absent from the model simulations. The researchers found that sea-level pressure trends showed the same difference. The differences are especially pronounced for the Indo-Pacific Warm Pool.

The contributions of the individual model ensemble members to several key climate indices is illustrated in the figure below, where the letters A to P denote the 16 model types and the horizontal lines show the range of actual observed trends.

The top panel shows the so-called Pacific SST gradient, or difference between western and eastern Pacific; the center panel shows the ratio of Indo-Pacific Warm Pool warming to tropical mean warming; and the bottom panel portrays the Southern Ocean SST. All indices are calculated as a relative rate of warming per degree Celsius of tropical mean SST change. It is clear that the researchers’ findings hold across all members of the ensemble.

The results suggest that computer climate models have systematic biases in the transient response of ocean temperature patterns to any anthropogenic forcing, say the research authors. That’s because the contribution of natural variability to multidecadal trends is thought to be small in the Indo-Pacific region.

To determine whether the difference between observations and models comes from internal climate variability or from climate forcing not captured by the models, the researchers conducted a signal-to-noise maximizing pattern analysis. This entails maximizing the signal-to-noise ratio in global temperature patterns, where the signal is defined as the difference between observations and the multimodel mean on 5-year and longer timescales, and the noise consists of inter-model differences, inter-ensemble-member differences, and less-than-5-year variability. The chosen ensemble had 160 members.

As seen in the next figure, the leading pattern from this analysis (Difference Pattern 1) shows significant discrepancies between observations and models, similar to the difference panel designated “e” in the first figure above. Lack of any difference would appear as a colorless pattern. Only one of the 598 ensemble members came anywhere close to matching the observed trend in this pattern, indicating that the models are the problem, not a misunderstanding of natural variability.

The second pattern (Difference Pattern 2), which focuses on the Northern Pacific and Atlantic Oceans, also shows an appreciable difference between models and observations. The research team found that only a handful of ensemble members could reproduce this pattern. They noted that the model that most closely matched the trend in Pattern 1 was furthest from reproducing the Pattern 2 trend.

Previously proposed explanations for the differences seen between observed and modeled trends in sea surface temperatures include systematic biases in the transient response to climate forcing, and model biases in the representation of multidecadal natural variability.

However, the paper’s authors conclude it is extremely unlikely that the trend discrepancies result entirely from internal variability, such as the anomalous return to warming during the recent cool phase of the PDO (Pacific Decadal Oscillation) as proposed by other researchers. The authors say that the large difference in the Warm Pool warming rate between models and observations (“b” in the second figure above) is particularly hard to explain by natural variability.

They suggest that multidecadal variability of both tropical and subtropical sea surface temperatures is much too weak in climate models. The authors suggest that damping feedbacks in response to Warm Pool warming may be too strong in the models, which would reduce both the modeled warming rate and the modeled amplitude of multidecadal variability.

Next: Are Ocean Surface Temperatures, Not CO2, the Climate Control Knob?

Recent Marine Heat Waves Caused by Undersea Volcanic Eruptions, Not Human CO2

In a previous post, I showed how submarine volcanic eruptions don’t contribute to global warming, despite the release of enormous amounts of explosive energy. But they do contribute to regional climate change in the oceans, such as marine heat waves and shrinkage of polar sea ice, explained a retired geologist in a recent lecture.

Wyss Yim, who holds positions at several universities in Hong Kong, says that undersea volcanic eruptions – rather than CO₂ – are an important driver of regional climate variability. The release of geothermal heat from these eruptions can explain oceanic heat waves, polar sea-ice changes and stronger-than-normal cycles of ENSO (the El Niño – Southern Oscillation), which causes temperature fluctuations and other climatic effects in the Pacific.

Submarine eruptions can eject basaltic lava at temperatures as high as 1,200 degrees Celsius (2,200 degrees Fahrenheit), often from multiple vents over a large area. Even though the hot lava is quickly quenched by the surrounding seawater, the heat absorbed by the ocean can have local, regional impacts that last for years.

The Pacific Ocean in particular is a major source of active terrestrial and submarine volcanoes, especially around the Ring of Fire bounding the Pacific tectonic plate, as illustrated in the figure below. Yim has identified eight underwater eruptions in the Pacific from 2011 to 2022 that had long-lasting effects on the climate, six of which emanated from the Ring of Fire.

One of these eruptions was from the Nishino-shima volcano south of Tokyo, which underwent a massive blow-out, initially undersea, that persisted from March 2013 to August 2015. Yim says the event was the principal cause of the so-called North Pacific Blob, a massive pool of warm seawater that formed in the northeast Pacific from 2013 to 2015, extending all the way from Alaska to the Baja Peninsula in Mexico and up to 400 meters (1,300 feet) deep. Climate scientists at the time, however, attributed the Blob to global warming.

The Nishino-shima eruption, together with other submarine eruptions in the Pacific during 2014 and 2015, was a major factor in prolonging and strengthening the massive 2014-2017 El Niño. A map depicting sea surface temperatures in January 2014, at the onset of El Niño and almost a year after the emergence of the Blob, is shown in the next figure. At that time, surface temperatures across the Blob were about 2.5 degrees Celsius (4.5 degrees Fahrenheit) above normal.

By mid-2014, the Blob covered an area approximately 1,600 km (1,000 miles) square. Its vast extent, states Yim, contributed to the gradual decline of Arctic sea ice between 2014 and 2016, especially in the vicinity of the Bering Strait. The Blob also led to two successive years without winter along the northeast Pacific coast.

Biodiversity in the region suffered too, with sustained toxic algal blooms. Yet none of this was caused by climate change.

The 2014-2017 El Niño was further exacerbated by the eruption from May to June 2015 of the Wolf volcano on the Galapagos Islands in the eastern Pacific. Although the Wolf volcano is on land, its lava flows entered the ocean. The figure below shows the location of the Wolf eruption, along with submarine eruptions of both the Axial Seamount close to the Blob and the Hunga volcano in Tonga in the South Pacific.

According to Yim, the most significant drivers of the global climate are changes in the earth’s orbit and the sun, followed by geothermal heat, and – only in third place – human-induced changes such as increased greenhouse gases. Geothermal heat from submarine volcanic eruptions causes not only marine heat waves and contraction of polar sea ice, but also local changes in ocean currents, sea levels and surface winds.

Detailed measurements of oceanic variables such as temperature, pressure, salinity and chemistry are made today by the worldwide network of 3,900 Argo profiling floats. The floats are battery-powered robotic buoys that patrol the oceans, sinking 1-2 km (0.6-1.2 miles) deep once every 10 days and then bobbing up to the surface, recording the properties of the water as they ascend. When the floats eventually reach the surface, the data is transmitted to a satellite.

Yim says his studies show that the role played by submarine volcanoes in governing the planet’s climate has been underrated. Eruptions of any of the several thousand active underwater volcanoes can have substantial regional effects on climate, as just discussed.

He suggests that the influence of volcanic eruptions on atmospheric and oceanic circulation should be included in climate models. The only volcanic effect in current models is the atmospheric cooling produced by eruption plumes.

Next: Climate Heresy: To Avoid Extinction We Need More, Not Less CO2

Ample Evidence Debunks Gloomy Prognosis for World’s Coral Reefs

According to a just-published research paper, dangers to the world’s coral reefs due to climate change and other stressors have been underestimated and by 2035, the average reef will face environmental conditions unsuitable for survival. This is scientific nonsense, however, as there is an abundance of recent evidence that corals are much more resilient than previously thought and recover quickly from stressful events.

The paper, by a trio of environmental scientists at the University of Hawai‘i, attempts to estimate the year after which various anthropogenic (human-caused) disturbances acting simultaneously will make it impossible for coral reefs to adapt and survive. The disturbances examined are marine heat waves, ocean acidification, storms, land use changes, and pressures from population density such as overfishing, farming runoff and coastal development.

Of these disturbances, the two expected to have the greatest future effect on coral reefs are marine heat waves and ocean acidification, supposedly exacerbated by rising greenhouse gas emissions. The figure to the left shows the scientists’ projected dates of environmental unsuitability for continued existence of the world’s coral reefs, assuming an intermediate CO2 emissions scenario (SSP2). The yellow curve is for marine heat waves, the green curve for ocean acidification.

You can see that the projected unsuitability rises to an incredible 75% by the end of the century for both perturbations, and even surpasses 50% for marine heat waves by 2050. The red arrow indicates the time difference at 75% unsuitability between heat waves considered alone and all disturbances combined (solid black curve).

But these gloomy prognostications are refuted by several recent field studies, two of which I discussed in an earlier blog post. The latest paper, published in May this year, reports on a 10-year study of coral-reef stability on Palmyra Atoll in the remote central Pacific Ocean. The scuba-diving researchers, from California’s Scripps Institution of Oceanography and Saudi Arabia’s King Abdullah University, discovered – by analyzing more than 1,500 digital images – that Palmyra reefs made a remarkable recovery from two major bleaching events in 2009 and 2015.

Bleaching occurs when the multitude of polyps that constitute a coral eject the microscopic algae that normally live inside the polyps and give coral its striking colors. Hotter than normal seawater causes the algae to poison the coral that then expels them, turning the polyps white. The bleaching events studied by the Palmyra researchers were a result of prolonged El Niños in the Pacific.

However, the researchers found that, at all eight Palmyra sites investigated, the corals returned to pre-bleaching levels within two years. This was true for corals on both a wave-exposed fore reef and a sheltered reef terrace. Stated Jennifer Smith, one of the paper’s coauthors,  “During the warming event of 2015, we saw that up to 90% of the corals on Palmyra bleached but in the year following we saw less than 10% mortality.”

The rapid coral recovery can be seen in the figure on the left below, showing the percentage of coral cover from 2009 to 2019 at all sites combined; FR denotes fore reef, RT reef terrace, and the dashed vertical lines indicate the 2009 and 2015 bleaching events. It’s clear there was only a small change in the reef’s coral and algae populations after a decade, despite the violent disruption of two bleaching episodes. A typical healthy reefscape is shown on the right.

Another 2022 study, discussed in my earlier post, came to much the same conclusions for a massive reef of giant rose-shaped corals hidden off the coast of Tahiti, the largest island in French Polynesia in the South Pacific. The giant corals measure more than 2 meters (6.5 feet) in diameter. Again, the reef survived a mass 2019 bleaching event almost unscathed.

Both these studies were conducted on relatively pristine coral reefs, free from local human stressors such as fishing, pollution, coastal development and tourism. But the same ability of corals to recover from bleaching events has been demonstrated in research on Australia’s famed Great Barrier Reef, many parts of which are subject to such stressors.

Studies in 2021 and 2020 (see here and here) found that both the Great Barrier Reef and coral colonies on reefs around Christmas Island in the Pacific were able to recover quickly from bleaching caused by the 2015-17 El Niño, even while seawater temperatures were still higher than normal. Recovery of the Great Barrier Reef is illustrated in the figure below, showing that the amount of coral on the reef in 2021 and 2022 was at record high levels, in spite of extensive bleaching a few years before.

Apart from making a number of arbitrary and questionable assumptions, the new University of Hawai‘i research is fundamentally flawed because it fails to take into account the ability of corals to rebound from potentially devastating events.

Next: Recent Marine Heat Waves Caused by Undersea Volcanic Eruptions, Not Human CO2

Challenges to the CO2 Global Warming Hypothesis: (7) Ocean Currents More Important than the Greenhouse Effect

A rather different challenge to the CO₂ global warming hypothesis from the challenges discussed in my previous posts postulates that human emissions of CO₂ into the atmosphere have only a minimal impact on the earth’s temperature. Instead, it is proposed that current global warming comes from a slowdown in ocean currents.

The daring challenge has been made in a recent paper by retired Australian meteorologist William Kininmonth, who was head of his country’s National Climate Centre from 1986 to 1998. Kininmonth rejects the claim of the IPCC (Intergovernmental Panel on Climate Change) that greenhouse gases have caused the bulk of modern global warming. The IPCC's claim is based on the hypothesis that the intensity of cooling longwave radiation to space has been considerably reduced by the increased atmospheric concentration of gases such as CO₂.

But, he says, the IPCC glosses over the fact that the earth is spherical, so what happens near the equator is very different from what happens at the poles. Most absorption of incoming shortwave solar radiation occurs over the tropics, where the incident radiation is nearly perpendicular to the surface. Yet the emission of outgoing longwave radiation takes place mostly at higher latitudes. Nowhere is there local radiation balance.

In an effort by the climate system to achieve balance, atmospheric winds and ocean currents constantly transport heat from the tropics toward the poles. Kininmonth argues, however, that radiation balance can’t exist globally, simply because the earth’s average surface temperature is not constant, with an annual range exceeding 2.5 degrees Celsius (4.5 degrees Fahrenheit). This shows that the global emission of longwave radiation to space varies seasonally, so radiation to space can’t define Earth’s temperature, either locally or globally.

In warm tropical oceans, the temperature is governed by absorption of solar shortwave radiation, together with absorption of longwave radiation radiated downward by greenhouse gases; heat carried away by ocean currents; and heat (including latent heat) lost to the atmosphere. Over the last 40 years, the tropical ocean surface has warmed by about 0.4 degrees Celsius (0.7 degrees Fahrenheit).

But the warming can’t be explained by rising CO₂ that went up from 341 ppm in 1982 to 417 ppm in 2022. This rise boosts the absorption of longwave radiation at the tropical surface by only 0.3 watts per square meter, according to the University of Chicago’s MODTRAN model, which simulates the emission and absorption of infrared radiation in the atmosphere. The calculation assumes clear sky conditions and tropical atmosphere profiles of temperature and relative humidity.

The 0.3 watts per square meter is too little to account for the increase in ocean surface temperature of 0.4 degrees Celsius (0.7 degrees Fahrenheit), which in turn increases the loss of latent and “sensible” (conductive) heat from the surface by about 3.5 watts per square meter, as estimated by Kininmonth.

So twelve times as much heat escapes from the tropical ocean to the atmosphere as the amount of heat entering the ocean due to the increase in CO₂ level. The absorption of additional radiation energy due to extra CO₂ is not enough to compensate for the loss of latent and sensible heat from the increase in ocean temperature.

The minimal contribution of CO₂ is evident from the following table, which shows how the amount of longwave radiation from greenhouse gases absorbed at the tropical surface goes up only marginally as the CO₂ concentration increases. The dominant greenhouse gas is water vapor, which produces 361.4 watts per square meter of radiation at the surface in the absence of CO₂; its value in the table (surface radiation) is the average global tropical value.

You can see that the increase in greenhouse gas absorption from preindustrial times to the present, corresponding roughly to the CO₂ increase from 300 ppm to 400 ppm, is 0.62 watts per square meter. According to the MODTRAN model, this is almost the same as the increase of 0.63 watts per square meter that occurred as the CO₂ level rose from 200 ppm to 280 ppm at the end of the last ice age – but which resulted in tropical warming of about 6 degrees Celsius (11 degrees Fahrenheit), compared with warming of only 0.4 degrees Celsius (0.7 degrees Fahrenheit) during the past 40 years.

Therefore, says Kininmonth, the only plausible explanation left for warming of the tropical ocean is a slowdown in ocean currents, those unseen arteries carrying the earth’s lifeblood of warmth away from the tropics. His suggested slowing mechanism is natural oscillations of the oceans, which he describes as the inertial and thermal flywheels of the climate system.

Kininmonth observes that the overturning time of the deep-ocean thermohaline circulation is about 1,000 years. Oscillations of the thermohaline circulation would cause a periodic variation in the upwelling of cold seawater to the tropical surface layer warmed by solar absorption; reduced upwelling would lead to further heating of the tropical ocean, while enhanced upwelling would result in cooling.

Such a pattern is consistent with the approximately 1,000-year interval between the Roman and Medieval Warm Periods, and again to current global warming.

Next: Ample Evidence Debunks Gloomy Prognosis for World’s Coral Reefs

Arctic Sea Ice Refuses to Disappear, despite Ever Rising Arctic Temperatures

The loss of sea ice in the Arctic due to global warming has long been held up by the mainstream media and climate activists as cause for alarm. The ice would be completely gone in summer, they predicted, by 2013, then 2016, then 2030. But the evidence shows that Arctic ice is not cooperating, and in fact its summer extent in 2022 was the same as in 2008. And this stasis has occurred even as Arctic temperatures continue to soar.

The minimum summer Arctic ice extent this month was about 67% of its coverage in 1979, which is when satellite measurements of sea ice in the Arctic and Antarctic began. The figure to the left shows satellite-derived images of Arctic sea ice extent in the summer of 2022 (September 18) and the winter of 2021 (March 7) , which was similar to 2022. Sea ice shrinks during summer months and expands to its maximum extent during the winter.

Over the interval from 1979 to 2022, Arctic summer ice detached from the Russian coast, although it still encases northern Greenland as can be seen. The figure below compares the monthly variation of Arctic ice extent from its March maximum to the September minimum, for the years 2022 (blue curve) and 2008 (red curve). The 2022 summer minimum is seen to be almost identical to that in 2008, as was the 2021 minimum, with the black curve depicting the median extent over the period from 1981 to 2010.

The next figure illustrates the estimated Arctic ice thickness and volume at the 2022 minimum. The volume depends on both ice extent and thickness, which varies with location as well as season. Arctic ice thickness is notoriously difficult to measure, the best data coming from limited submarine observations.

The thickest, and oldest, winter ice currently lies along the northern coasts of the Canadian Arctic Archipelago and Greenland. According to a trio of Danish research institutions, just 20% of the Arctic ice pack today consists of thick ice more than one to two years old, compared to 40% in 1983. Thick, multi-year ice doesn’t melt away in the summer, but much of the ice cover currently formed during winter consists of thin, first-year ice. 

What is surprising, however, is that the lack of any further loss in summer ice extent since 2008 has been accompanied by a considerable increase in Arctic temperature. The left panel of the next figure, from a dataset compiled by the European Union’s Copernicus Climate Change Service, shows the mean surface temperature in the Arctic since 1979.

You can see that the Arctic has been warming steadily since at least 1979, when the first satellite measurements were made. As shown in the figure, the mean temperature there shot up by 3 degrees Celsius (5.4 degrees Fahrenheit), compared to global warming over the same interval of only 0.68 degrees Celsius (1.2 degrees Fahrenheit). That’s an Arctic warming rate 4 times faster than the globe as a whole. From 2008 to 2022, during which the summer ice extent remained unchanged on average, the Arctic nevertheless warmed by about 1.3 degrees Celsius (2.3 degrees Fahrenheit).

This phenomenon of excessive warming at the North Pole is known as Arctic amplification, depicted numerically in the right panel of the figure above. The effect shows strong regional variability, with some areas – such as the Taymyr Peninsula region in Siberia and the sea near Novaya Zemlya Island – warming by as much as seven times the global average. The principal reason for the high amplification ratio in these areas is exceptionally low winter ice cover, which is most pronounced in the Barents Sea near Novaya Zemlya.

The amplification is a result of so-called albedo (reflectivity) feedback. Sea ice is covered by a layer of white snow that reflects around 85% of incoming sunlight back out to space. As the highly reflective ice melts from global warming, it exposes more of the darker seawater underneath. The less reflective seawater absorbs more incoming solar radiation than sea ice, pushing the temperature higher. This in turn melts more ice and exposes more seawater, amplifying the warming in a feedback loop.

Interestingly, computer climate models, most of which exaggerate the impact of global warming, underestimate Arctic warming. The models typically estimate an average Arctic amplification ratio of about 2.5, much lower than the average ratio of 4 deduced from actual observations. A recent research study attributes this difference to possible errors in the modeled sensitivity to greenhouse gas forcing, and in the distribution of heating from the forcing between the atmosphere, cryosphere and ocean.

They also suggest that climate models underestimate multi-decadal internal variability, especially of atmospheric circulation in mid-latitudes (30^o to 60^o from the equator), which influences temperature variability in the Arctic as well.

Next: Climate-Related Disasters Wrongly Linked to Global Warming by Two International Agencies

No Evidence That Hurricanes Are Becoming More Likely or Stronger

Despite the claims of activists and the mainstream media that climate change is making major hurricanes – such as U.S. Hurricane Harvey in 2017 or Hurricane Katrina in 2005 – more frequent and stronger, several recent studies have found no evidence for either of these assertions.

In fact, a 2022 study reveals that tropical cyclones in general, which include hurricanes, typhoons and tropical storms, are letting up as the globe warms. Over the period from 1900 to 2012, the study authors found that the annual number of tropical cyclones declined by about 13% compared with the period between 1850 and 1900, when such powerful storms were actually on the rise.

This is illustrated in the figure below, showing the tropical cyclone trend calculated by the researchers, using a combination of actual sea-level observations and climate model experiments. The solid blue line is the annual number of tropical cyclones globally, and the red line is a five-year running mean. 

The tropical cyclone trend is almost the opposite of the temperature trend: the average global temperature went down from 1880 to 1910, and increased by approximately 1.0 degrees Celsius (1.8 degrees Fahrenheit) between 1910 and 2012. After 1950, the rate of cyclone decline accelerated to about 23% compared to the 1850-1900 baseline, as global warming increased during the second half of the 20th century. Although the study authors noted a variation from one ocean basin to another, all basins demonstrated the same downward trend.

The authors remark how their findings are consistent with the predictions of climate models, in spite of the popular belief that a warming climate will spawn more, not fewer, hurricanes and typhoons, as more water evaporates into the atmosphere from the oceans and provides extra fuel. At the same time, however, tropical cyclone formation is inhibited by wind shear, which also increases as sea surface temperatures rise.    

Some climate scientists share the view of the IPCC (Intergovernmental Panel on Climate Change)’s Sixth Assessment Report that, while tropical cyclones overall may be diminishing as the climate changes, the strongest storms are becoming more common, especially in the North Atlantic. The next figure depicts the frequency of all major North Atlantic hurricanes back to 1851. Major hurricanes in Categories 3, 4 or 5 have a top wind speed of 178 km per hour (111 mph) or higher.

You can see that hurricane activity in this basin has escalated over the last 20 years, especially in 2005 and 2020. But, despite the upsurge, the data also show that the frequency of major North Atlantic hurricanes in recent decades is merely comparable to that in the 1950s and 1960s – a period when the earth was cooling rather than warming.

A team of hurricane experts concluded in a 2021 study that, at least in the Atlantic, the recent apparent increase in major hur­ricanes results from improvements in observational capabilities since 1970 and is unlikely to be a true climate trend. And, even though it appears that major Atlantic hurricanes were less frequent before about 1940, the lower numbers simply reflect the rela­tive lack of measurements in early years of the record. Aircraft re­connaissance flights to gather data on hurricanes only began in 1944, while satellite coverage dates only from the 1960s.

The team of experts found that once they corrected the data for under­counts in the pre-satellite era, there were no significant recent increases in the frequency of either major or all North Atlantic hurricanes. They suggested that the reduction in major hurricanes between the 1970s and the 1990s, clearly visible in the figure above, could have been the result of natural climate variability or possibly aerosol-induced weakening.

Natural climate cycles thought to contribute to Atlantic hurricanes include the AMO (Atlantic Multi-Decadal Oscillation) and La Niña, the cool phase of ENSO (the El Niño – Southern Oscillation). The AMO, which has a cycle time of approximately 65 years and alternates between warm and cool phases, governs many extremes, such as cyclonic storms in the Atlantic basin and major floods in eastern North America and western Europe. In the U.S., La Niñas influence major landfalling hurricanes.

Just as there’s no good evidence that global warming is increasing the strength of hurricanes, the same is true for their typhoon cous­ins in the northwestern Pacific. Although long-term data on major typhoons is not available, the frequency of all typhoon categories combined appears to be un­changed since 1951, according to the Japan Meteorological Agency. Yet a new study demonstrates a decline in both total and major typhoons for the 32-year period from 1990 to 2021, reinforcing the recent decrease in global tropical cyclones discussed above.

Next: Are Current Hot and Cold Extremes Climate Change or Natural Variability?

No Convincing Evidence That Cleaner Air Causes More Hurricanes

According to a new research study by NOAA (the U.S. National Oceanic and Atmospheric Administration), aerosol pollution plays a major role in hurricane activity. The study author claims that a recent decline in atmospheric pollutants over Europe and the U.S. has resulted in more hurricanes in the North Atlantic Ocean, while a boost in aerosols over Asia has suppressed tropical cyclones in the western Pacific.

But this claim, touted by the media, is faulty since the study only examines changes in aerosol emissions and hurricane frequency since 1980 – a selective choice of data becoming all too common among climate scientists trying to bolster the narrative of anthropogenic climate change. The aerosol pollution is mostly in the form of sulfate particles and droplets from industrial and vehicle emissions. When pre-1980 evidence is included, however, the apparent connection between aerosols and hurricanes falls apart.

Let’s look first at the North Atlantic. Data for the Atlantic basin, which has the best quality data in the world, do indeed show heightened hurricane ac­tivity over the last 20 years, particularly in 2005 and 2020. You can see this in the following figure, which illustrates the frequency of all major Atlantic hurricanes as far back as 1851. Major hurricanes (Category 3 or greater) have a top wind speed of 178 km per hour (111 mph) or higher. The recent enhanced activity is less pronounced, though still noticeable, for Category 1 and 2 hurricanes.

The next figure shows the observed increase in Atlantic hurricane frequency (top), from the 20 years between 1980 and 2000 to the 20 years between 2001 and 2020, compared to the NOAA study’s simulated change in sulfate aerosols during the same interval (bottom).

The hurricane frequency TCF is for all (Categories 1 through 5) hurricanes, with positive and negative color values denoting higher and lower frequency, respectively. A similar color scheme is used for the sulfate calculations. Both the Atlantic increase and western Pacific decrease in hurricane frequency are clearly visible, as well as the corresponding decrease and increase in aerosol pollution from 1980 to 2020.

But what the study overlooks is that the frequency of major Atlantic hurricanes in the 1950s and 1960s was at least compara­ble to that in the last two decades when, as the figure shows, it took a sudden upward hike from the 1970s, 1980s and early 1990s. If the study’s conclusions are correct, then pollution levels in Europe and the U.S. during the 1950s and 1960s must have been as low as they were from 2001 to 2020.

However, examination of pollution data for the North Atlantic reveals that the exact opposite is true: European and U.S. aerosol concentrations in the 1960s were much higher than in any later decade, including decades after 1980 during the study period. This can be seen in the figure below, which depicts the sulfate concentration in London air over the 50 years from 1962 to 2012; similar data exists for the U.S. (see here, for example).

Were the NOAA study valid, such high aerosol levels in European and U.S. skies during the 1960s would have decreased North Atlantic hurricane activity in that period – the reverse of what the data demonstrates in the first figure above. In the Pacific, the study links a supposed reduction in tropical cyclones to a well-documented rise in aerosol pollution in that region, due to growing industrial emissions.

But a close look at the bottom half of the second figure above shows the increase in pollution since 1980 has occurred mostly in southern Asia. The top half of the same figure indicates increased cyclone activity near India and the Persian Gulf, associated with higher, not lower pollution. The only decreases are in the vicinity of Japan and Australia, where any changes in pollution level are slight.

The NOAA study aside, changes in global hurricane frequency are much more likely to be associated with naturally occurring ocean cycles than with aerosols. Indeed, NOAA has previously linked increased Atlantic hurricane activity to the warm phase of the Atlantic Multidecadal Oscillation (AMO).

The AMO, which has a cycle time of approximately 65 years and alternates between warm and cool phases, governs many extremes, such as cyclonic storms in the Atlantic basin and major floods in eastern North America and western Europe. The present warm phase began in 1995, triggering a more tempestuous period when both named Atlantic storms and hurricanes have become more common on average.

Another contribution to storm activity in the Atlantic comes from La Niña cycles in the Pacific. Apart from a cooling effect, La Niñas result in quieter conditions in the eastern Pacific and enhanced activity in the Atlantic. In the U.S., major landfalling hurricanes are tied to La Niña cycles in the Pacific, not to global warming.

Next: Why There’s No Need to Panic about Methane in the Atmosphere