July 21, 2016, by Alex Kirby
The Antarctic peninsula shows wide natural climate variability.
Image: Courtesy of British Antarctic Survey
After warming for nearly 50 years the Antarctic peninsula has begun cooling, though probably not for long, UK scientists say.
LONDON, 21 July, 2016 – Life is full of surprises, not least the climate. The Antarctic Peninsula, part of which reported spectacularly high temperatures as recently as last year, is now in a cooling phase.
Scientists from the British Antarctic Survey (BAS), based in Cambridge, UK, www.bas.ac.uk say the warming which occurred on the peninsula from the early 1950s to the late 1990s has paused.
But they say they know at least some of the reasons for the change, and that if greenhouse gas concentrations continue to rise at their current rate, temperatures will increase across the peninsula by several degrees Celsius by the end of this century.
It is the slowing rate of ozone loss and the climate’s natural variability, the researchers say, that were “significant in bringing about the change” to a temporary cooling phase. But temperatures remain higher than measured during the middle of the last century, and glaciers are still retreating.
“The Antarctic peninsula is one of the most challenging places on Earth on which to identify the causes of decade-to-decade temperature changes“
Writing in the journal Nature, researchers from BAS describe how the stabilisation of the ozone hole and changing wind patterns have driven a regional cooling phase that is temporarily masking the warming influence of greenhouse gases.
In the last month, atmospheric levels of carbon dioxide above Antarctica rose past the 400 parts per million (ppm) milestone, contrasting with the pre-industrial level of 280 ppm recorded in Antarctic ice cores.
Average temperatures on the peninsula rose by about 0.5⁰C each decade from the early 1950s until the late 1990s, when the researchers found they began falling at the same rate..
The lead author, Professor John Turner of BAS, says: “The Antarctic peninsula is one of the most challenging places on Earth on which to identify the causes of decade-to-decade temperature changes.
“The Antarctic peninsula climate system shows large natural variations, which can overwhelm the signals of human-induced global warming . . . Even in a generally warming world, over the next couple of decades, temperatures in this region may go up or down, but our models predict that in the longer term greenhouse gases will lead to an increase in temperatures by the end of the 21st century.”
During the last century the temperature rise of up to 0.5⁰C each decade on the peninsula helped to trigger the collapse of ice shelves and caused many glaciers to retreat.
While sea ice extent around the peninsula fell towards the end of the last century it has been increasing in recent years, particularly in the north-east of the region. The cold easterly winds observed this century have had a greater impact on the region because the sea ice has prevented ocean heat from entering the atmosphere.
The researchers also looked at a 2,000-year climate reconstruction using the chemical signals in ice cores. This suggested that peninsula warming over the whole twentieth century was unusual, but not unprecedented in the context of two millennia.
Climate model simulations predict that if greenhouse gas concentrations continue to increase at currently projected rates their warming effect will predominate over natural variability and the cooling effect associated with recovering ozone levels, producing several degrees of warming across the region by the end of this century.
The researchers’ study needs to be seen in context. The area they examined is about 1% of the entire Antarctic continent and is an area roughly the size of England.
Eric J. Steig, of the University of Washington, US, wrote: “Even before Turner and colleagues’ analysis, there was little evidence that the rapid warming in Antarctica falls outside the range of natural variability. . . In short, Turner and co-workers’ findings should not be surprising.”
But the work by the BAS team, if not an outright surprise, is still a valuable reminder that natural limits can vary widely, and that well-intentioned adjustments to the climate in one area (limiting ozone loss, for example, or efforts to reduce air pollution) can have unpredictable consequences elsewhere.
It is a reminder as well that, so far as science can see, the inexorable trend of present fossil fuel use is towards more warming and greater disruption. – Climate News Network
Alex Kirby is a former BBC journalist and environment correspondent. He now works with universities, charities and international agencies to improve their media skills, and with journalists in the developing world keen to specialise in environmental reporting.