Climate activists have long lamented the supposedly impending demise of Arctic sea ice due to global warming. But, despite the constant drumbeat of apocalyptic predictions, the recently reached minimum extent of Arctic ice in 2021 is no smaller than it was back in 2008.  And at the other end of the globe, the sea ice around Antarctica has been expanding for at least 42 years.

Scientific observations of sea ice in the Arctic and Antarctic have only been possible since satellite measurements began in 1979. The figure below shows satellite-derived images of Arctic sea ice extent in the summer of 1979 (left image), and the summer (September) and winter (March) of 2021 (right image, with September on the left). Sea ice shrinks during summer months and expands to its maximum extent during the winter.

Over the interval from 1979 to 2021, Arctic summer ice extent decreased by approximately 30%; while it still embraces northern Greenland, it no longer reaches the Russian coast. The left graph in the next figure compares the monthly variation of Arctic ice extent from its March maximum to the September minimum, for the years 2021 (blue curve) and 2008 (green curve). The 2021 summer minimum is seen to be almost identical to that in 2008, with the black curve depicting the median extent over the period from 1981 to 2010.

The right graph in the figure shows the estimated month-by-month variation of Arctic ice volume in recent years. The volume depends on both ice extent and its thickness, which varies with location as well as season – the thickest, and oldest, winter ice currently lying along the northern coasts of the Canadian Arctic Archipelago and Greenland.

Arctic ice thickness is notoriously difficult to measure, the best data coming from limited submarine observations. According to one account based on satellite data, more than 75% of the Arctic winter ice pack today consists of thin ice just a few months old, whereas in the past it was only 50%. However, these estimates are unreliable and a trio of Danish research institutions that monitor the Arctic estimate that the ice volume has changed very little over the last 17 years, as seen in the figure above.

Another indication that Arctic ice is not melting as fast as climate activists claim is the state of the Northwest Passage – the waterway between the Atlantic and Pacific Oceans through the Arctic Ocean, along the coast of North America. Although both the southern and northern routes of the Northwest Passage have been open intermittently since 2007, ice conditions this year are relatively severe compared to the past two decades: thicker multiyear ice is the main hazard. The northern deep-water route is already choked with ice and will not open until at least next year.

In the Antarctic, sea ice almost disappears completely during the southern summer and reaches its maximum extent in September, at the end of winter. This is illustrated in the satellite-derived images below, showing the summer minimum (left image) and winter maximum extent (right image) in 2021. The Antarctic winter sea ice extent is presently well above its long-term average.

In fact, despite the long-term loss of ice in the Arctic, the sea ice around Antarctica has expanded slightly during the satellite era, as shown in the following figure up to 2020. Although the maximum Antarctic ice extent (shown in red) fluctuates greatly from year to year, and took a tumble in 2017, it has grown at an average rate between 1% and 2% per decade (dashed red line) since 1979.

Note that the ice losses shown in this figure are “anomalies,” or departures from the monthly mean ice extent for the period from 1981 to 2010, rather than the minimum extent of summer ice. So the Arctic data don’t reveal how the 2021 minimum was almost identical to 2008, as illustrated in the earlier figures.

Several possible reasons have been put forward for the greater fluctuations in Antarctic winter sea ice compared to that in the Arctic. One analysis links the Antarctic oscillations to ENSO (the El Niño – Southern Oscillation), a natural cycle that causes variations in mean temperature and other climatic effects in tropical regions of the Pacific Ocean. The Pacific impinges on a substantial portion of the Southern Ocean that surrounds Antarctica.

The analysis suggests that the very large winter ice extents of 2012, 2013 and 2014 were a consequence of the 2012 La Niña, which is the cool phase of ENSO. Reinforcing that idea is the fact that this year’s surge in ice extent follows another La Niña earlier in 2021; the big loss of sea ice in 2017 could be associated with 2016’s strong El Niño, the warm phase of ENSO. The natural Pacific Decadal Oscillation may also play a role.

Next: Ice Sheet Update (1): Evidence That Antarctica Is Cooling, Not Warming