A recently published study on high and low temperatures across the continental United States has received significant attention in the US. (see Science Daily (4 stars), NY Times, Google News Search). It can best be seen graphically (copyright U.C.A.R., graphic by Mike Shibao).
While I think this graphic is compelling enough it actually understates the problem, if weather was in a relative steady state, you would expect statistically that the number of weather extreme events would tend to zero as more and more years went by. That is obviously just not happening. The Science Daily article goes into much more detail.