The XKCD blog posted a comic about climate change the other day, aimed at those who say 'the climate has changed before'. Well for as long as humans have been progressing as an intelligent species it hasn't changed much like we are looking forward to in the next 50/100 years. This is unknown territory for a cultivating species.

It's a 'back of the envelope' type drawing (heavily smoothed out/uses all sorts of data) but it makes a fair point.

http://xkcd.com/1732/

I love seeing things in perspective like this. This one is scary as fuck.

4.5 billion years ago the Earth's surface was made of molten lava. So I guess if something were to happen to bring that about again, it wouldn't be a bad thing.

Hmmm.
It does bring it home quite forcibly, doesn't it?

But still not with sufficient clarity. What we're facing isn't just some changes in temperature or rainfall or whatever while we carry on more or less as normal. In many areas whole ecosystems are going to collapse - coral reefs for example - and human systems of food production (which are finely-tuned to specific types of climate) are going to be blown wide open.