Another way to test climate change - from the late Stephen Schneider, a sharp mind, author, and an influential climate scientist:
what we've done is gone to the literature and looked at a couple of thousand studies, and we simply asked, of all these observations made by these ecologists over the last, say, 20 to 50 years, how many are reporting changes in when trees flower, when birds lay eggs, when they migrate from the tropics to the high latitudes? And what we found was, although the majority of species aren't showing it yet, there is a minority of species showing change.
So then we said, okay, how many of them are coming back the way you would expect from physiological theory? Namely, if it's getting warmer, the flowering should be earlier, if it's getting warmer they should come back from the tropics earlier, and so forth. And it turns out about 80% of the species that are changing are changing in the direction you would predict. That is an unbelievably loaded coin, that's about 700 species. If you took a coin and flipped it 700 times and 80% of the times it came up heads, you'd be pretty sure that was a loaded coin, and we're pretty sure that we have a clear discernable signal of the recent temperature warming on plants and animals.
From A tribute to Stephen Schneider, on the Science Show, 31 July 2010 (audio & transcript available). Emphasis added.