This is a temperature chart for Central Park, NY. It gets a lot of play in the press as a "common sense" proof of global warming, and comes right off the NASA climate site:
Now, lets ignore the fact that urbanization could be causing a local temperature increase that does not reflect a general climate trend. Lets, however, select our time frame a little differently. Lets take the whole data set, which goes back further, rather than this set chosen by activists to make their point. The same data over a longer trend looks like this:
OOPS! Gee, I am not sure Central Park looks much warmer. In fact, you could argue it is cooler. Hmmmm. Ask yourself if you really think it was an accident that the year with the single lowest temperature in the middle of the second graph was used as the starting point for the first.