Bill Burroughs: One storm doesn't make global warming

We have to accept that every so often, with orwithout global warming, we will be hit hard.

"What's all this stuff about global warming?" I hear you say. An understandable question, in the circumstances. Every time some "freak" weather strikes, a standard response is to attribute it to global warming. It matters not whether it is heat and drought in summer, snowstorms or avalanches in winter, or gales and floods at any time, the reaction is always the same. But is there any justification for this hyperbole?

"What's all this stuff about global warming?" I hear you say. An understandable question, in the circumstances. Every time some "freak" weather strikes, a standard response is to attribute it to global warming. It matters not whether it is heat and drought in summer, snowstorms or avalanches in winter, or gales and floods at any time, the reaction is always the same. But is there any justification for this hyperbole?

For instance, how do this week's floods compare with those of the past? Then, if they are truly exceptional, is there any reason to think the climate is becoming more extreme, and, if so, could human activities be causing this change?

As climatic events go, floods are not easy to rank. While the high mark can easily be recorded on the walls of buildings, how much the event relates to changes in the drainage characteristics of the land is more difficult to say. Building on the floodplain, or paving over urban areas can all increase the peak flood levels.

Across the country, the floods seem to have been the worst since 1947, although in the south-east of England those of 1968 were probably worse. But when it comes to extremes, 1947 was the Real McCoy, the coldest February in the last 300 years and a winter that precipitated a fuel crisis that brought the country to its knees. Then the wettest March in over two centuries combined with melting snow to produce awful floods, only to be followed by the warmest May to September on record. What a year! But no one in 1947 talked about global climate change.

As for recent rainfall records, for England and Wales, September and October this year has been the wettest comparable period since 1903, narrowly surpassing 1976, when a deluge ended the hottest, driest summer in more than 300 years. Although 1903 featured the wettest September and October since the mid-18th century, there have been wetter two-month periods at other times of the year.

So, while recent events are pretty awful, they are not really so far out of line with past experience. As for whether they are becoming more common as part of global warming, the evidence is not convincing. The one thing that is certain is that the global temperature has risen by about 0.6C (1F) in the last century or so.

The Intergovernmental Panel on Climate Change (IPCC), which has produced the definitive assessment on the nature of climate change, concluded in 1995 that human activities exerted a discernible influence in this rise. Its next report is due out next year, and is likely to endorse this conclusion.

But when it comes to more extreme weather, the IPCC finds little evidence of any trend. The arguments as to whether we should expect a warmer world to have more extreme weather are at best equivocal. On the one hand, warmer oceans, especially in the tropics, are likely to pump more water vapour into the atmosphere, leading to more intense tropical cyclones and heavier rainfall episodes. On the other hand, the computer models predict that polar regions will warm more than the tropics. This will reduce the temperature gradient in mid-latitudes, which drives the vigorous depressions that bring us high winds and rain, and so will reduce the chances of these events here.

Climate records show little evidence of any significant trend in the number of tropical cyclones around the world. Similarly, analysis of gales in our part of the world show no marked trend over the last century, although there was a marked upsurge of deep depressions in the North Atlantic in the late 1980s and early 1990s.

All in all, there is little to show that the warming during the 20th century has led to any significant increase in extreme weather around the world.

Certainly, there's good reason for hoping the variability of climate does not increase as a result of the build-up of greenhouse gases in the atmosphere. Because, if it started to react suddenly and unpredictably to a significant rise in temperature, the consequences could be dramatic. One scenario is that global ocean circulation could flip, in effect switching off the Gulf Stream, with dire implications for Europe.

All in all, the best that we can hope for is to keep global warming down to a level that leaves the natural variability of the climate largely unchanged. Modest rises in temperature here will reduce the frequency and intensity of frosts in winter, and give us a few more hot summers. As for floods and gales, it looks as if we will continue to get the mixture much as before. Even so, this is sufficient reason in itself to look more closely at whether planning controls for developments in urban and suburban areas were ever really properly geared to the natural variability of our climate.

In truth, the worst weather in 50 years will always be awful. So we have to accept that, every now and then, with or without global warming, we will be hit hard. To the extent that we may be altering the climate, that is good reason for doing as much as is economically and politically feasible to minimise our impact.

Substantial action will not be easy. As the other big story of the week has made clear, high fuel taxes, which both reduce emissions of greenhouse gases and raise revenues to fund infrastructure investments such as flood protection schemes, are not yet seen by most people as being an acceptable solution. All the hyperbole about extreme weather hasn't helped move the debate in the right direction.

The author's latest book, 'The Climate Revealed', is published by Mitchell Beazley at £25