For a while it was up to 45 degrees Celsius warmer than normal in some places on the Antarctic ice sheet!

Temperatures were measured in East Antarctica in the last week that researchers – at this time of year – would not have thought possible. For example, a temperature of -11.5 degrees Celsius was measured at the research station Concordia Station high on the Antarctic ice sheet on Friday. That may not seem impressive, but it is – for this time of year and for this location – extremely high. “That’s the highest temperature ever recorded there,” said Jonathan Wille, a polar meteorology researcher at the Université Grenoble Alpes in France. “And it is 40-45 degrees Celsius higher than the average temperature measured here in March. That’s really impressive. And it surpasses the previous heat record set in March by 20 degrees Celsius.”

From Dumont d’Urville to Vostok

But the mercury rose to unprecedented levels in other places in Antarctica as well. For example, a temperature of 4.9 degrees Celsius was measured at the Dumont d’Urville research station located on the coast. A new record for the month of March. Meanwhile, Casey Station — also on the coast of East Antarctica but thousands of miles from Dumont d’Urville — recorded a temperature of 5.6 degrees Celsius. “That surpassed the previous temperature record recorded in March by 1.5 degrees.” But a record was also broken at the Russian research station Vostok – which, like Concordia, is located deep inland and high on the ice sheet and is normally very cold. “On March 18, a temperature of -17.7 degrees Celsius was measured,” says Wille. And such high temperatures had never been observed before in the month of March.

terrifying

“These temperatures are really exceptional,” concludes Wille. It should be noted, however, that temperature measurements in Antarctica do not go back as far as elsewhere on Earth; most Antarctic research stations were not rigged until well into the twentieth century. It means that what we now see as unparalleled measurements may in reality be more frequent than we think. That said, the high temperatures recorded over the past week deserve our full attention. “Because they are redefining the way we see the Antarctic climate system. And the events are also terrifying in that regard, because we are now seeing weather conditions in Antarctica that we never thought possible before – especially in an area that contains so much ice.”

Atmospheric Rivers

While researchers are still amazed by the high temperatures measured in East Antarctica, they think they can explain them. The high temperatures could be traced back to so-called ‘atmospheric rivers’. According to the KNMI these are “river-shaped wisps of concentrated water vapor transport in the atmosphere”. In addition to water vapor, these atmospheric rivers often also transport heat. Both the moisture and heat come from lower latitudes and are transported to higher latitudes by the atmospheric rivers. “In this case, on Tuesday, March 15, there was a very intense atmospheric river arriving on the east coast of Antarctica,” Wille says. “And when that happened, there was a lot of precipitation. That too is something that is very rare for this area. In addition, there was significant melting on the east coast – again something that almost never happens, especially in March. After March 15, there was what we call an atmospheric blockage.” It meant that the moisture transported by the Atmospheric River to East Antarctica couldn’t get out. “Instead, it was driven inland, resulting in the high temperatures we saw later in the week at research stations further inland – such as Concordia and Vostok.”

The fact that such an atmospheric river even succeeds in raising the mercury – first on the coast and later also inland – has everything to do with the enormous amount of moisture that this ‘river’ carries with it. “The Antarctic continent is what we also call a polar desert: there is almost no moisture in the atmosphere. Now it is true that an atmosphere that contains a lot of moisture can also accommodate more heat. So if an enormous amount of moisture is transported to the Antarctic continent, you automatically have to deal with an air mass that is much warmer. In addition, the atmospheric river also brings clouds. And those clouds are different from the clouds we normally see over Antarctica, which are made up of ice particles. The clouds brought by the atmospheric river contain liquid water. And those clouds of liquid water bring radiation (from the sun and therefore also heat, ed.) to the surface, but prevent it from escaping from that surface back into the higher atmosphere. In fact, they act as a blanket and thus warm up the surface.”

Climate change

Those atmospheric rivers are part of the weather system. Moreover, they perform frequently and in many places. According to the KNMI, for example, they occur in Western Europe alone about once every ten days. With all that in mind, the fact that an atmospheric river has now wreaked havoc in Antarctica may seem to be largely due to the weather, rather than the climate. And yet there may also be a link with climate change, says Wille. “It (the high temperatures in Antarctica, ed.) fits into a pattern of extreme events that we’ve seen in recent years that researchers and meteorologists thought were impossible. We had the extreme heat wave in the Pacific Northwest in June 2021, which was meteorologically thought to be impossible.” And which researchers later showed would have been impossible in the absence of anthropogenic warming. “We had the floods in Germany a month later: also an event that was the result of an extreme weather pattern.” And of which it was later also shown that climate change had made that impossible weather pattern a lot more likely. The high temperatures that have now been measured in Antarctica clearly fit effortlessly into the list of ‘weather conditions deemed impossible that nevertheless made an appearance’. “But it is still unclear whether this event can also be attributed to climate change. That has two reasons. First of all, we need time to study this event and figure out what circulation pattern led to the influx of moist air over Antarctica. And secondly, as mentioned, we have a fairly short observation history in Antarctica, so it could just be that this is an event that naturally occurs once every 100 years on average and that we are only now seeing for the first time. ”

A lot of melt, but still profit

Whether the high temperatures were partly made possible by anthropogenic warming remains to be seen for the time being. But what is certain is that temperatures have led to significant melting in East Antarctica. However, that’s not something you need to worry about. “Because this is an area where melting rarely occurs, there are hardly any consequences,” explains Wille. “The meltwater freezes again very quickly, so this is not something that will unbalance the glaciers or have other nasty consequences. In fact, the movement of such a warm, moisture-filled air mass over the Antarctic ice sheet has resulted in very heavy snowfall across much of Antarctica.” And so the atmospheric river is adding more ice to East Antarctica than it has taken away.”

Nervous

So no large-scale adverse consequences for Antarctica. Where the atmospheric river does cause quite a lot of chunks, however, is in the beautiful models and theories that researchers have rigged to describe the Antarctic weather system. “This event completely changes our view and understanding of the Antarctic weather,” Wille said. “I have spoken to various researchers about this and we are now scratching our heads. It makes us all a little nervous. Because this event didn’t cause much melt, but we are now wondering: what if this had happened in the middle of summer in West Antarctica and led to massive melts on sensitive glaciers such as Thwaites Glacier and other glaciers that flow into sea ​​and contribute to sea level rise? That’s something we don’t know now and actually thought it was impossible, but now that this has happened, we have been given something to think about. Perhaps it is a possibility that we should take into account.”

In the meantime, the mercury in East Antarctica has already dropped considerably. “We saw the high temperatures especially last Thursday and Friday, during the weekend it remained quite warm and on Monday the mercury started to drop again. And now everything is back to normal in East Antarctica. The last time I checked, the temperature at Concordia Station was again around -40 degrees Celsius, which is typical for this time of year.” And with that the ‘Antarctic heat wave’ is over. For researchers, however, it is only just beginning. In the coming period – many times longer than the actual heat wave lasted – they will ponder how these exceptional temperatures could occur and how realistic it is that they will again appear elsewhere in Antarctica in the future and cause major damage. cause.