A recent report from Friends of the Earth begins with the question: "What's wrong with the weather?" To support its argument that there is indeed something wrong, the writers of the report list an impressive variety of freak weather events over the past few years. To mention just a few: the nine hottest years on record have all occurred in the last 14 years; England had the wettest June this century; the strongest ever hurricane was reported in the Eastern Pacific; the number of blizzards and heavy storms in the US has increased by 20 per cent since 1990.
It all makes an impressive-sounding list, and Friends of the Earth see it all as a warning about the consequences of global warming. "There is no disputing the fact that since the late 19th century global mean surface temperature has increased by between 0.3 and 0.6C and that recent years have been among the warmest since 1860, when the global temperature record began."
The main suspect in this report is, as you may have guessed, greenhouse gases. The droughts, storms and forest fires are only what one would expect from man's ceaseless habit of pumping heat-retaining gases into the air. As the Inter-Governmental Panel on Climate Change says: "small changes in the mean climate or climate variability can produce large changes in the frequency of extreme events." And as El Nino keeps reminding us, you need only a pool of warm water in the Pacific to turn normal weather patterns upside down throughout half (or perhaps more) of the globe.
Since the Friends of the Earth report appeared, we have seen California bracing itself for "the mother of all storms", while Vietnam last weekend was hit by its strongest ever storm. Putting all these events together does indeed make it seem as though something has gone wrong with the world's weather.
There are, however, two equally compelling arguments against the above theories. First, we are, on a geological time-scale, still coming out of the little ice age that lasted from the 17th century to the beginning of the 19th. Temperatures have been rising since then because we're still warming up. Anyway, we're going through a period of relative temperature stability, so we rather overestimate the significance of half a degree or so.
The second argument is more statistical. Precise weather records have been kept only since about 1860. With 12 months in a year, and hundreds of countries in the world, and temperatures, rainfall, wind speeds and other variables all being recorded, and various time-cycles of weather interacting, you really ought to expect new records to be set quite frequently. It's just a question of waiting for an extreme of weather to turn up at a point where one happens to be measuring.
Paradoxically, weather extremes are normal. We just haven't been measuring the weather long enough to know whether the current epidemic of extremes is anything out of the ordinary.