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Absence of Antarctic Peninsula warming is within natural variability
The Antarctic Peninsula warmed for much of the twentieth century, but beginning in the late 1990s, the warming trend switched to cooling, finds a paper published in Nature this week. These findings are within natural variability of regional atmospheric circulation and do not imply more general cooling in Antarctica or elsewhere.
Research stations on the Antarctic Peninsula have recorded warming near-surface air temperatures since the 1950s with several interlinked processes suggested as contributing to the warming, including sea-ice loss, westerly winds and stratospheric ozone depletion.
John Turner and colleagues use a stacked temperature record from six stations in the northern Antarctic Peninsula to investigate broad-scale temperature changes in the region since 1979. They find that there has been an absence of regional warming since the late 1990s up to 2014, with the annual mean temperature decreasing at a statistically significant rate. The most rapid cooling occurs during the Southern Hemisphere summer, they note. They consider this cooling trend to be a consequence of a greater frequency of cold, easterly to southeasterly winds resulting from more cyclonic conditions in the northern Weddell Sea, in turn associated with a strengthening mid-latitude jet stream.
The authors stress that their findings cover only one per cent of the Antarctic continent and emphasise that these decadal temperature changes in the region are not primarily associated with the drivers of global temperature change, and instead reflect the extreme natural internal variability of the regional atmospheric circulation.
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Professor Nerilie Abram is a climate scientist at the Australian National University and a fellow of the Australian Academy of Science
This new research definitely doesn’t imply that warming of the planet has stopped. But it is a good example of how the long-term changes in our climate also have a layer of year-to-year variability on top that can cause some decades to warm particularly quickly and others to apparently not warm at all. For a remote place like Antarctica, where climate measurements are especially short and those year-to-year swings in climate are very large, our records really aren’t long enough yet to see the full picture of human-caused climate change.
One of the ways that we can get around the problem of short climate records in Antarctica is to reconstruct how the climate has changed in the past. Scientists do this by measuring the chemical makeup of the layers of ice that buildup year after year to form Antarctica’s vast ice sheets. Ice cores from the Antarctic Peninsula show that the rapid warming that was happening prior to this recent pause was part of a long term trend that began around the 1930s and was unusually fast but not completely unprecedented compared to natural climate changes over the last 2000 years.
Professor Timothy Naish is Director of the Antarctic Research Centre at Victoria University of Wellington
This is a really interesting new study and confirms the conclusion of earlier research (cited in the news and views), that the 20th and 21st century warming trends in west Antarctica were not unusual in the context of natural climate variability of the last 2000 years.
Natural climate processes that control the timing and strength of the El Niño–Southern Oscillation and the Southern Annular Mode are thought to be responsible for the observed decadal variability.
This new paper by Turner et al. focusses specifically on the temperature records of the Antarctic Peninsula, which has often been referred to as a “global warming hot spot”.
So while some skeptics may see this paper as an apparent “debunking”, the IPCC made it clear in its 5th Assessment that, unlike the Arctic, overall Antarctica had not warmed any faster than the global average temperature increase since the mid-20th century, and that regional rapid warming observed on the Antarctic Peninsula could not be attributed to anthropogenic global warming.
It also noted that during past warmer-than-present climates, when carbon dioxide levels reached 400ppm or more, Antarctica did display an amplified warming pattern up to two times more than the global average.
Amplified warming of the southern polar region is thought to take longer than its northern hemisphere counterpart because of the role that the deep, well-mixed Southern Ocean plays as a heat sink and potentially because of the role the ozone hole plays in suppressing powerful feedbacks associated with sea-ice retreat.
The message is that this is not a surprise, that amplified warming of Antarctica is expected and is predicted as greenhouse concentrations increase.
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