October 30, 2008 – Original Source: New Scientist. By Andy Coghlan
Evidence has emerged that human activity, not natural phenomena, is directly responsible for heating up the polar ice caps.
The news coincides with announcements earlier this week that the Arctic ice is now thinner than at any time since records began.
“We knew the warming was happening there, especially in the Arctic,” says Alexey Karpechko of the Climatic Research Unit at the University of East Anglia, UK, but pinning down the causes has not been possible until now.
Karpechko, head of the team which concluded that human activity is to blame, says their findings show at last that all continents of the world are being warmed through human activity. “The Antarctic was the only one where there was any doubt, but not any more,” he says.
“It’s confirmation of expected results,” says Gilles Sommeria, deputy secretary of the Intergovernmental Panel on Climate Change, the international alliance of scientists monitoring climate change. “It shows that human influence already observed in most regions is confirmed in Antarctica, where the data were scarcer.”
To find out whether human activity was to blame at the poles, Karpechko and colleagues analysed temperature data collected at the poles over the past century.
They ran the data through two sets of computerised climate models. Both sets factored in the effects of natural phenomena, such volcanic eruptions and solar sunspot cycles, but only one set factored in the consequences of human activities that can affect climate, such as rising levels of the greenhouse gas carbon dioxide and fluctuations in the amount of ozone in the stratosphere.
It was the models which included human factors that most closely matched the temperature profiles recorded at the poles. “For me, it can’t be more clear that human activity is responsible,” says Karpechko.
Ironically, the models found that warming would have been even more marked if the ozone layer which cuts out harmful solar radiation had not been depleted by the chlorofluorocarbon chemicals once used in aerosols.
“If we fix the ozone layer, warming could get even stronger,” says Karpechko. “But at the same time, things will get even worse if we keep emitting greenhouse gases,” he says.
Meanwhile, research just published in Geophysical Research Letters (DOI: 10.1029/2008GL035710) reveals that the thickness of ice in the western Arctichas plunged by around 49 centimetres – almost a fifth compared with the average reading over the previous five winters. This is the region that saw the North-West passage open in 2007.
The team behind this study, led by Katharine Giles of the Centre for Polar Observation and Modelling at University College London, used reflected satellite radar pulses to deduce that the ice had thinned over the Arctic as a whole by 26 centimetres on average, about 10% of the average thickness over the previous five winters.