The Climate in Emergency

A weekly blog on science, news, and ideas related to climate change

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Hot News from Down South

The latest climate news to light up social media is that Antarctica has hit a new, all-time record high of 63° F.

According to CNBC,

A single temperature event doesn’t make a trend, but it’s a situation worth watching, said Jordan Gerth, a researcher at the Cooperative Institute for Meteorological Satellite Studies. “One rare temperature doesn’t tell us a whole lot,” Gerth said. “But if we see these events happening more frequently over the next decade or so, it could be a larger story to tell.”

This comment is a strange one. I’m going to give Dr. Gerth the benefit of the doubt and assume he is being misrepresented or misunderstood, somehow, but the implications of the quote are worth discussing.

It is quite true that one event does not make a trend. Without context, an extreme weather event is not evidence of anything because even if our climate were not changing, the occasional hot day would still occur. To find the footprint of climate change, you need to look at weather records over time. But then, why can’t we just look at Antarctica’s weather records over time and determine if there is a trend? Dr. Gerth appears to think we can’t do that for some reason, but must look to the future instead. Either that, or his words might be taken to mean global warming has not been conclusively spotted in Antarctica yet.

And that is rather patently not true.

I am inclined to think Dr. Gerth meant that there isn’t enough data on Antarctic weather to draw conclusions. Frankly, I don’t see how there could be much weather data on the frozen continent, given how sparsely populated it is and how recent the human presence is there. There are, indeed, weather stations on Antarctica, some of them the better part of a century old, though their records are not necessarily continuous–but there aren’t very many of them. Until the age of weather satellites, there must have been huge swaths of the continent where any weather could have been happening at all and no one would know. The signal of climate only emerges from the noise of weather once you have about thirty years of data to look at and the satellite temperature record is only 37 years old.

Antarctica is also fairly big and some of its associated islands (including the sites of the recent temperature records) are actually well outside the Antarctic Circle. The emotional punch of the headline (“Antarctica tops 60°!”) is a bit misleading, given the tendency of the outside world to equate all of Antarctica with the South Pole.

And yet we do have a fairly simple way to tell that Antarctica’s temperatures are indeed going up; the sea level is rising. About half of the observed rise is due to melting ice, as opposed to thermal expansion and other factors, and much of that ice was in Antarctica. Even if we had no weather data for that continent at all, we would know its climate is warming.

We also do have long-term climate data for the south of the world,quite apart from weather stations. The glacial ice records evidence of temperature, along with other important information, such as atmospheric composition, in layers, for thousands of years. A British team drilled in and got a sample some years back:

What the scientists discovered, however, removed any doubt. “We found that the peninsula has been warming for the past 600 years,” said lead author Robert Mulvaney, of the British Antarctic Survey, in an interview. “But the rate of warming has been much faster during the past century, and fastest over the past 50 years.”

From this and other studies, we know that Antarctica is warming, and is in fact warming faster than anywhere else in the world. Also, Antarctica is not the only place that has set a new heat record recently: Equatorial Guinea, Ghana, Samoa, and the Wallis and Futuna Territory have all either set or tied their high temperature records in 2015. Five national or territorial heat records in a year not quite four months old yet is remarkable, especially as exactly zero have set cold records (sorry, Boston).

So why did CNBC quote Dr. Gerth as saying there is no larger story to tell?

There is, in fact, a regional story here as well as a global one, and it’s an oddly familiar story for those of us in the United States since it involves the polar vortex.

Polar vortexes are not some unusual type of winter storm, popular media representations to the contrary. Instead, they are simply the cold air masses around the poles. The boundaries between these air masses and more temperate air are quite abrupt and marked by currents of upper-air winds–the jet streams. The location of the boundary changes, sometimes developing huge meanders that bring unusual temperatures to unusual places. Over the past few years, we in the United States have seen several such events in which the Southeast of our country froze while Alaska (and many other places) saw record warmth.

The recent unusual warmth in parts of Antarctica is also due to a wavy polar boundary and was also associated with unusually cold temperatures (even for Antarctica) elsewhere on the continent. The same wind pattern was also responsible for the other major climate-related news story, the flooding of the Atacama Desert, in Chile. While the rainstorms only brought about an inch of water, that is as much as the area usually gets in fourteen years. And with little vegetation to absorb water or stabilize the ground, the floods were dramatic.

Now, I’ve written before about the link between melting Arctic sea ice and the recently wavy polar boundary, but I do not know if an equivalent process is at work in the south. It may well not be, since Antarctic sea ice is actually expanding. The sea and air are both steadily warming, but both are still cold enough to allow ice to form in the Southern Sea–meanwhile, wind and water currents that previously limited sea ice are changing, allowing more ice to form (sea ice has no effect on lea level; the land-based ice that does influence sea level is melting rapidly).

So, is this particular extreme weather event related to global warming in an clear, causal way? I do not know. But when an entire system changes, it is unrealistic to expect any corner of that system to remain untouched.