Global greenhouse crises of the past

Greg Retallack, Univ. of Oregon (http://www.uoregon.edu/~gregr/)

The coming global warming due to burning of fossil fuels is not
unprecedented in the geological past. Past spikes in carbon dioxide levels
in the atmosphere inferred from the microscopic study of fossil leaves
followed rare catastrophes such as asteroid impact and unusually large
volcanic eruptions. These past events had a range of severity and can be
studied as previews of what is to come. Not only will climate be warmer,
wetter, and more seasonal, but more and more species will go extinct.