Antarctic Peninsula warming: natural variability or “global warming”?

Most people know that the Antarctic Peninsula is one of the most rapidly warming places on earth. But like everywhere else in Antarctica, the length of available temperature data is short — most records begin in 1957 (when stations were put in place during the International Geophysical Year); a few start in the late 1940s. This makes the recent rapid warming difficult to evaluate; in general, what’s interesting is how the trend compares with the underlying variability. As anyone who’s been there can tell you, the weather on the Antarctic Peninsula is pretty wild, and this applies to the climate as well: year to year variability is very large. Put another way, the noise level is high, and discerning the signal requires more data than is available from the instrumental temperature record. This is where ice cores come in handy — they provide a much longer record, and allow us to evaluate the recent changes in a more complete context.

A new paper in Nature this week presents results from an ice core drilled by the British Antarctic Survey (BAS) at James Ross Island on the Antarctic Peninsula. Before discussing the results, congratulations are due to Rob Mulvaney and his team for obtaining the ice core in the first place, quite apart from the analyses. James Ross Island is a gorgeous place to work on a sunny summer day, but it can be brutal on a bad day, and the BAS team spent many months in the field. The record they obtained is some 50,000 years long — by far the longest record ever obtained on the Antarctic Peninsula. (James Ross Island’s ice cap was originally cored by a Argentine/French team back in the 1980s, but they obtained just a 400 year record).

Figure 1.The glaciated summit of Mt. Haddington, site of a new ice core record reported by Mulvaney et al., as viewed from Santa Marta Cove, James Ross Island, on a nice summer day. (photo: E. Steig).

So do Mulvaney et al.’s results allow us to discern signal from noise? The short answer is yes, but it’s not that simple. This is quite apparent from the reporting on the paper, most of which has been pretty accurate, yet with headlines running the gamut from saying that the cause of recent warning is “unclear” (NPR) or “part of longer trend” (Australian Broadcasting Corp.), to “most warming in Antarctic is human caused” (Climate Central) and a more subdued “ususual but not unique” from the BBC.

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