Heavy Weather: All around the World, Extreme Weather Events Are Becoming More Frequent and More Severe. and While the UK Has Been Hit by Several Devastating Floods in Recent Years, Developing Countries Continue to Be Profoundly Affected, with Pakistan an Obvious Recent Example. Some Climate Scientists Point to These Disasters as the Inevitable Effects of Man-Made Climate Change, but Can a Causal Link Be Proven?

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It has been a year of extremes in the northwest of England. Last November, Cumbria suffered some of the worst flooding in the UK's recorded history. The River Derwent flooded Cockermouth, causing one death and 100million [pounds sterling] worth of damage. A single day saw 314 millimetres of rain fall, a 24-hour record for the UK, yet within seven months, the local water company had issued a drought order after the region's driest start to the year in more than 70 years.

Such extreme and erratic weather--devastating floods, severe droughts, hurricanes, snowstorms and heat waves--is occurring around the world, and often with far greater intensity and loss of life than the Lake District experienced. Conventional wisdom suggests that something is up with the planet's weather, and the perceptions of this change are striking in that they are geographically widespread.

The World Meteorological Organization (WMO)--drawing on climate data from networks of land-based weather and climate stations, ships and buoys from its 189 member states--reported that most parts of all continents experienced above-normal temperatures last year. Maximum daily temperatures in northern China were routinely above 40[degrees]C, breaking historical records; Australia had its third-warmest year on record, marked by three exceptional heat waves, one of which brought Victoria's highest recorded temperature (48.8[degrees]C) and the worst bushfires in the country's history.

Rainfall was also marked by extremes. China suffered its worst drought in five decades, with water levels in some reservoirs dropping to 50-year lows; India endured one of its weakest monsoons since 1972; drought in Kenya caused severe damage to livestock and a 40 per cent decline in the maize harvest; Mexico experienced severe-to-exceptional drought; and drought in central Argentina caused severe damage to agriculture, livestock and water resources.

Meanwhile, the northern plains of the USA were affected by record flooding, and the Amazon Basin had its second-worst floods in 100 years. Other areas experienced unprecedented bursts of intense rainfall: in Burkina Faso, 263 millimetres of rain, the highest in 90 years, was recorded in less than 12 hours; more than 300 millimetres was recorded in less than 48 hours in southeastern Spain, where the long-term annual average is 450 millimetres; and the highest September rainfall in 80 years produced severe flash floods in northwestern Turkey. Havoc also came in the form of extreme storms, with Ontario in particular experiencing record numbers of tornadoes and related fatalities.

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MOUNTING EVIDENCE

Such weather extremes have always occurred, but scientists are now scrutinising and recording these events in search of evidence that they are increasing and that they are linked to climate change.

In 2007, the Intergovernmental Panel on Climate Change reported that there was 'strong statistical evidence' for a systemic change in extreme weather in some parts of the world, and the WMO is in no doubt. 'There are data we've collected over the world for more than a century,' says Omar Baddour, the WMO's head of data management. 'We can characterise an extreme event as one occurring less than ten per cent of the time when looking in the historical archives. We can say with confidence that extremes are becoming more frequent in many parts of the world.'

The consensus among forecasters is equally emphatic. In 2006, tropical cyclone researchers and forecasters gathered at a WMO meeting agreed that it was likely that some increase in tropical cyclone peak windspeed and rainfall will occur if the climate continues to warm. Model studies and theory, they announced, projected a three to five per cent increase in wind speed per degree Celsius increase of tropical sea-surface temperatures.

Simple science reinforces such a view, according to Bob Ward, policy director of the Grantham Research Institute on Climate Change and the Environment at the London School of Economics. …