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?