Some critics of anthropogenic climate change argue that since the earth has warmed before, it isn't such a big deal if it does so again today.
I think they're right.
By all accounts, the universe will keep expanding, the moon will still circle us, and the earth is going to keep spinning, with or without global warming. The earth itself doesn't give a damn about global warming. Carbon levels have risen before, they've fallen before, and the world has not ended.
Scientists in Nature published data last month for the lowest 200 meters of Dome C (an ice core in the Antarctic). Here's one of their figures:
The black dots on the bottom right (650,000-800,000 years ago) represent the most recent data from this ice core, and they've placed temperature data from a different ice core above. It doesn't take a geophysicist to see that there's a correlation between the two data sets.
But there's one other inference that most people aren't drawing from this type of climate data. It's that temperatures have risen before, and they've always eventually fallen. Based on that graph, it usually takes about 25,000 years for the carbon levels to drop from their peaks to average levels of CO2.
Which means that no matter how high CO2 levels and temperatures reach, they will eventually come down. The earth is going to be fine.
Global warming will not be the end of the world.
Luthi D, Le Floch M, Bereiter B, Blunier T, Barnola J-M, Siengenthaler U, Raynaud D, Jouzel J, Fischer H, Kawamura K, Stocker T F. 2008. High-resolution carbon dioxide concentration record 650,000-800,000 years before present. Nature 453: 379-382. doi:10.1038/nature06949.