Weather Runs Hot and Cold, So Scientists Look to the Ice

Published The Straits Times, 30 Mar 2012

NEW YORK: Some people call what has been happening the past few years 'weather weirding' and this month is turning out to be a fine example.

As a surreal heatwave was peaking across much of the United States last week, pools and beaches drew crowds, some farmers planted their crops six weeks early, and trees burst into bloom.

Lurching from one weather extreme to another seems to have become routine across the Northern Hemisphere. Parts of the US may be shivering now, but Scotland is setting heat records.

Across Europe, people died by the hundred during a severe cold wave in the first half of last month, but a week later revellers in Paris were strolling down the Champs-Elysees in their shirtsleeves.

Does science have a clue to what is going on? The short answer appears to be: not quite.

The longer answer is that researchers are developing theories that, should they withstand scrutiny, may tie at least some of the erratic weather to global warming. Specifically, suspicion is focused on the drastic decline of sea ice in the Arctic, which is believed to be a direct consequence of the human release of greenhouse gases.

'The question really is not whether the loss of the sea ice can be affecting the atmospheric circulation on a large scale,' said Ms Jennifer Francis, a Rutgers University climate researcher. 'The question is, how can it not be, and what are the mechanisms?'

As the planet warms, many scientists say, more energy and water vapour are entering the atmosphere and driving weather systems.

'The reason you have a clothes dryer that heats the air is that warm air can evaporate water more easily,' said Mr Thomas Peterson, a researcher with the National Oceanic and Atmospheric Administration.

A report released on Wednesday by the Intergovernmental Panel on Climate Change, the United Nations body that issues periodic updates on climate science, confirmed that a strong body of evidence links global warming to an increase in heatwaves, a rise in episodes of heavy rainfall and other precipitation, and more frequent coastal flooding.

'A changing climate leads to changes in the frequency, intensity, spatial extent, duration and timing of extreme weather and climate events, and can result in unprecedented extreme weather and climate events,' the report found.

It was drawn up by 220 scientists and economists from 62 countries, who pored over thousands of published studies. It focuses on how to make people and their assets - homes, farms, stores, office buildings, infrastructure - more resilient to the intense droughts, floods and storms projected for the coming decades.

Since the 1950s, record-breaking daily temperatures and heatwaves have become more frequent or lasted longer, according to strong evidence. There is a 90 per cent to 100 per cent probability that this will continue through the 21st century, the report said.

'The hottest day, which today occurs once every 20 years, is expected to occur once every second year by the end of the 21st century,' said climate physicist Thomas Stocker.

Other documented imbalances in the climate have certainly become remarkable. US government scientists recently reported, for instance, that last month was the 324th consecutive month in which global temperatures exceeded their long-term average for a given month; the last month with below-average temperatures was February 1985.

But, while the link between heatwaves and global warming may be clear, the evidence is much thinner regarding some types of weather extremes.

Scientists studying tornadoes are plagued by poor statistics that could be hiding significant trends, but so far, they are not seeing any long-term increase in the most damaging twisters. And researchers studying specific events, like the Russian heatwave of 2010, have often come to conflicting conclusions about whether to blame climate change.

Scientists who dispute the importance of global warming have long ridiculed any attempt to link greenhouse gases to weather extremes. Mr John Christy, a climate scientist at the University of Alabama in Huntsville, told the US Congress last year that 'the weather is very dynamic, especially at local scales, so that extreme events of one type or another will occur somewhere on the planet every year'.

Yet mainstream scientists are determined to figure out which climate extremes are being influenced by human activity.

NEW YORK TIMES, REUTERS, AGENCE FRANCE-PRESSE