Almost 4 years ago the Intergovernmental Panel on Climate change
told us that climate change is "very likely" to increase the frequency of heat waves and heavy precipitation.1
The same may be true for hurricanes.2
It's now common after extreme weather events to hear some people suggest that those events were caused by global warming. Careful scientists, however, point out that weather is extremely variable. It always has been. It always will be. Climate change refers to a change in the average conditions, so attributing any one event to climate change will always be fraught with difficulty.
Indeed, here's what the authors of a paper published in today's Nature
have to say about attributing increased flooding to climate change:
Recent widespread UK floods--such as in spring 1998, autumn 2000, winter
2003 and summer 2007--have prompted debate as to whether these particular
events are attributable to anthropogenic climate change6, 7, 13, 14, 15.
This is an ill-posed question, given uncertainty in the antecedent
conditions; many untraceable factors, anthropogenic or natural, may have
contributed to any individual event13, 16.
Indeed, observed UK fluvial-flood and high-flow trends for recent
decades suggest no clear evidence for any change above that of natural
variability17, 18, mirroring the mixed picture in observed precipitation changes19, 20.
Translating that to English: Asking whether recent floods in the UK are the result of climate change is asking a question that can't be answered. Too many variables influence particular weather events in complicated ways to make any answer plausible.
Does that mean the IPCC was wrong? Not at all. In fact, both the paper just quoted and another one
in the same issue suggest that "global warming resulting from anthropogenic emissions of greenhouse gases may have compounded the effects of such fluctuations", as Richard Allan writes in an accompanying commentary
on the articles. And how can we be so sure that extreme weather is more likely when we can't attribute any single event to global warming? Read on.