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Today the world faces global warming, but 34 million years ago a distinctly chillier menace was sweeping our planet.
Average temperatures around the world plunged nearly 15 degrees Fahrenheit (8.2 degrees Celsius) during a span of hundreds of thousands of years, according to a new study.
The cooling was so severe that it likely led to the extinction of many of North America's reptiles and amphibians.
The cause of the temperature shift was a change in the level of greenhouse gases—specifically carbon dioxide—the study shows.
Researchers believe an increase in carbon dioxide is mainly responsible for the global warming occurring today.
