The weekend storm across the Irish Sea was not the worst England ever had. It is, however, the most recent in a long line of spectacular, and often tragic, weather events around the world that have made people wonder if the nemesis of climate change is finally upon us. Are these extreme happenings a direct result of global warming, a consequence of our affluent society - or would they just have happened anyway, even if the amount of carbon dioxide and other greenhouse gases in the atmosphere remained the same as two centuries ago?
Theories about climate change can be divided into at least two broad categories. First, there are the facts - or at least those findings which we believe to be facts. We know the average temperature of our planet has increased by about half a degree Celsius since 1860, and that the rate of warming has increased significantly in recent years. Last year, for example, was the fifth warmest on record, and in addition, it was no less than the 21st consecutive year with an above-normal, average global temperature. To draw the picture even more succinctly, the year before that, 1998, was the warmest year, in the warmest decade, in the warmest century of the last millennium.
It is also true that there is a consensus in the scientific community that this increase in global temperature is more than can be plausibly explained by natural and normal climatic variations. As the experts put it, "The balance of evidence suggests a discernible human influence on global climate." Indeed they go even further. Scientists, collectively and authoritatively, say they cannot explain the unusual global warmth of recent years without including the effects of greenhouse gases introduced by humans. They point out that since 1976 the world has been warming at a rate equivalent to two degrees Celsius per century, a rate they describe as "unprecedented" in the last 1,000 years, and which can only be explained by taking account of human influence. Looking to the future, we also know that the best climate models available today predict that unless action is taken to significantly restrict greenhouse gas emissions, the average temperature of the world is likely to increase by a further two degrees Celsius or so in the next 100 years, with sea levels rising by a foot or two.
All this we know. What we fear is that many of the unusually severe weather events of recent years - the apparent increase in the frequency and ferocity of hurricanes, the seemingly unusual droughts and floods in many parts of the world, and the unusually strong El Nino not so long ago - may all have been triggered by this observed increase in global temperature.
There is no firm evidence that they have been. Moreover, for every extreme event, a previous occurrence of similar severity can be identified. For example, the weekend storm in Britain is described as the worst since the October storm of 1987, but this, as it were "by definition", means that there was a worse storm 13 years ago. And neither of these events seems comparable to the Great Storm of 1703 in Britain, or our own "Night of the Big Wind" in 1839.
None the less, the suspicion that some, at least, of the extreme events of recent years may be connected to the increase in average global temperature is justifiable. In a warmer world there is more evaporation from the Earth's surface; one can think of such a process as extracting extra energy from the world's oceans and injecting it into the atmosphere, there to provide potential extra fuel for more vigorous weather systems. And indeed there is some, albeit not conclusive, evidence that in the past 20 years mid-Atlantic depressions have become deeper and more intense.
Moreover, climate models predict that in a greenhouse world there should be more precipitation in the mid-latitudes and near the poles, and less near the Equator, and there is some evidence that this is happening; it is a small step from this to attributing certain catastrophic floods and droughts to global warming.
BUT then other scientists point to anomalous warming at the poles, saying this reduces the temperature contrast with the lower latitudes, and that it should mean fewer and less vigorous storms. Indeed they remind us that it is hard enough to understand the processes which underlie explosive storm development in the present climate, never mind predicting how storms might behave in an even warmer world.
What is not in doubt, however, is that the balance of opinion is slowly shifting as the years go by, as more and more severe events attract attention, and as our scientific understanding of the processes involved improves. It is a sign of the times that less than a year ago the chief executive of the British Meteorological Office and his opposite number in the US, scientists to whom the best possible advice must be available, jointly issued a well-considered statement which included this:
"Our new data and understanding now point to the critical situation we face; to slow future change we must start taking action soon. At the same time, we must start to learn to live with the likely consequences - more extreme weather, rising sea levels, changing precipitation patterns, ecological and agricultural dislocations, and the increased spread of human disease."
We have been warned, it seems.
Brendan McWilliams, a former assistant director of Met Eireann, works with the European Meteorological Satellite Organisation in Darmstadt, Germany.