Well, the dramatic rise … and particularly that which is believed to be human-caused … has occurred mainly in the latter ~third of this century.
They have various (less accurate) proxy indicators to estimate global temperatures going back hundreds and even hundreds of thousands of years.
This just in, 2002 will be the second warmest year ever recorded.
http://ens-news.com/ens/dec2002/2002-12-11-10.asp
The golbal greenhouse effect can be demonstrated, just look at Venus.
As for the idea of an alarmist media, I remember reading in a letter from the editor of Discover magazine that, although he felt global climate change was the most important scientific issue of our time, he seldom put it on the cover of the magazine because it always depressed sales.
I don’t think this prevents people from studing it though.