Professor of Earth and Space Sciences and Astrobiologist for NASA, Peter Ward (Book Link) discussed his vision of the end of the world based on past mass extinctions.

While most scientists agree that a meteor impact killed the dinosaurs 65 million years ago, Ward said our planet's 15 other ancient mass extinctions were caused by short-term global warming. According to Ward, high levels of CO2 increased global temperatures, contributing to conditions that gave rise to a series of bacteria in the oceans that produced toxic hydrogen sulfide gas. Eventually, this gas erupted into the atmosphere and poisoned animals and plants on the planet's surface.

Atmospheric CO2 is currently at 380 ppm and rising 2 ppm every year, Ward explained. He said the geological record indicates 'greenhouse extinctions' occur when CO2 levels go beyond 1000 ppm and when all the ice caps have melted. Ward estimated that we have 1000 years before this mass extinction process begins, unless we begin reducing man-made CO2 emissions now. In the meantime, we can expect a host of problems, including coastal flooding and food shortages, caused by rising sea levels, he warned.