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Antarctica Has Just Had Its First Recorded Heatwave

While the world rightfully focuses on the COVID-19 pandemic, the planet is still warming. This summer's Antarctic weather, as elsewhe...


While the world rightfully focuses on the COVID-19 pandemic, the planet is still warming. This summer's Antarctic weather, as elsewhere in the world, was unprecedented in the observed record.

Our research, published today in Global Change Biology, describes the recent heatwave in Antarctica. Beginning in late spring east of the Antarctic Peninsula, it circumnavigated the continent over the next four months. Some of our team spent the summer in Antarctica observing these temperatures and the effect on natural systems, witnessing the heatwave first-hand.

Antarctica may be isolated from other continents by the Southern Ocean, but has worldwide impacts. It drives the global ocean conveyor belt, a constant system of deep-ocean circulation that transfers oceanic heat around the planet, and its melting ice sheet adds to global sea level rise.

Antarctica represents the simple, extreme end of conditions for life. It can be seen as a 'canary in the mine,' demonstrating patterns of change we can expect to see elsewhere.

A heatwave in the coldest place on Earth
Most of Antarctica is ice-covered, but there are small ice-free oases, predominantly on the coast. Collectively 0.44 percent of the continent, these unique areas are important biodiversity hotspots for penguins and other seabirds, mosses, lichens, lakes, ponds and associated invertebrates.

This summer, Casey Research Station, in the Windmill Islands oasis, experienced its first recorded heat wave. For three days, minimum temperatures exceeded zero and daily maximums were all above 7.5 degrees Celsius. On January 24, its highest maximum of 9.2 degrees Celsius was recorded, almost 7 degrees Celsius above Casey's 30-year mean for the month.

The arrival of warm, moist air during this weather event brought rain to Davis Research Station in the normally frigid, ice-free desert of the Vestfold Hills. The warm conditions triggered extensive meltwater pools and surface streams on local glaciers. These, together with melting snowbanks, contributed to high-flowing rivers and flooding lakes.

By February, most heat was concentrated in the Antarctic Peninsula at the northernmost part of the continent. A new Antarctic maximum temperature of 18.4 degrees Celsius was recorded on February 6 at Argentina's Esperanza research station on the Peninsula—almost 1 degree Celsius above the previous record. Three days later this was eclipsed when 20.75 degrees Celsius was reported at Brazil's Marambio station, on Seymour Island east of the Peninsula.

What caused the heatwave?
The pace of warming from global climate change has been generally slower in East Antarctica compared with West Antarctica and the Antarctic Peninsula. This is in part due to the ozone hole, which has occurred in spring over Antarctica since the late 1970s.

The hole has tended to strengthen jet stream winds over the Southern Ocean promoting a generally more 'positive' state of the Southern Annular Mode in summer. This means the Southern Ocean's westerly wind belt has tended to stay close to Antarctica at that time of year creating a seasonal 'shield', reducing the transfer of warm air from the Earth's temperate regions to Antarctica.

But during the spring of 2019 a strong warming of the stratosphere over Antarctica significantly reduced the size of the ozone hole. This helped to support a more 'negative' state of the Southern Annular Mode and weakened the shield.

Other factors in late 2019 may have also helped to warm Antarctica. The Indian Ocean Dipole was in a strong 'positive' state due to a late retreat of the Indian monsoon. This meant that water in the western Indian Ocean was warmer than normal. Air rising from this and other warm ocean patches in the Pacific Ocean provided energy sources that altered the path of weather systems and helped to disturb and warm the stratosphere.

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