The following material was developed from a three part series recently published by The Scientific American, entitled Our Extreme Future: Predicting and Coping with the Effects of a Changing Climate. (Errors and omissions are mine.)
One of the predictions of climate change models is that extreme weather — floods, heat waves, droughts, even blizzards — will become far more common.
Scientists used to say, cautiously, that extreme weather events were “consistent” with the predictions of climate change. No more. Now they can make the statement that particular events would not have happened the same way without global warming, and the data show that the number of such events is rising.
Figures indicate a trend towards an increase in extreme weather events that can only be fully explained by climate change and many individual events would not have happened in the same way without global warming.
Why? Basic physics is at work: “The planet has already warmed roughly one degree Celsius since pre-industrial times, thanks to CO2 and other greenhouse gases emitted into the atmosphere. And for every one-degree C rise in temperature, the amount of moisture that the atmosphere can contain and hold rises by seven per cent, a multi-fold increase,” explains Peter Stott, head of climate monitoring and attribution at the U.K. Met Office’s Hadley Center for Climate Change.
The increased moisture in the atmosphere inevitably means more rain. That’s obvious. But not just any kind of rain, the climate models predict. Because of the large-scale energy balance of the planet, “the upshot is that overall rainfall increases only two to three per cent per degree of warming, whereas extreme rainfall increases six to seven per cent,” Stott says.
Scientists say that an event with a clear global warming component was hurricane Katrina. They calculate that the combination of overall planetary warming, elevated moisture in the atmosphere, and higher sea-surface temperatures meant that four to six per cent of the precipitation — an extra 2.5 cm of rain — in Katrina was due to global warming.
Apart from everything else, what we can say for sure is that, as with Katrina, this extreme weather would not have happened the same way without global warming.
But the real honest message is that while there is debate about how much extreme weather climate change is inducing now, there is very little debate about its effect in the future.