In my last post I mentioned that climate change is defined as a change in a distribution. I thought it might help to see what that looks like. The data that you see here is observed data, not a projection or a model.
What it shows is the distribution of summer temperatures in North Americarelative to what is normal for that time of year. The horizontal units are in terms of standard deviations, instead of degrees. So a very hot day (i.e., 10 degrees greater than normal) would be plotted as +2 standard deviations (obviously I’m making up the numbers here for effect).
The gist is that climate has already changed (the probability of the shift you see being a product of random variation is vanishingly small). If you believe that humans are the cause of this shift, then you should believe it will continue to change.
(borrowed from the great James Hansen)