A computer simulation of the Earth's climate 250 million years ago suggests that global warming triggered the so-called "great dying". A dramatic rise in carbon dioxide caused temperatures to soar to 10 to 30 degrees Celsius higher than today, say US researchers. The warming had a profound impact on the oceans, cutting off oxygen to the lower depths and extinguishing most lifeforms, they write in the latest issue of Geology. The research adds to the growing body of evidence that higher temperatures, rather than a giant space rock hitting the planet, led to the greatest mass extinction in history.