It is impossible to pin any single unusual weather event on global warming, but emerging evidence suggests that global warming is already influencing the weather. (earthobservatory.nasa.gov)
In the past the negative effect of unusual weather events was always temporary; within a year or two things would return to normal. (earth-policy.org)
Peter Stott of the UK Met Office in Exeter headed a project looking at six unusual weather events in 2011. (newscientist.com)