56 million years ago, the Earth experienced a brief, cataclysmic hot spell now known as the Paleocene-Eocene Thermal Maximum, or PETM.
After heat-trapping carbon leaked into the sky from an unknown source, the planet, which was already several degrees Celsius hotter than it is today, gained an additional six degrees.
The PETM another episodes of intense warming were more extreme than theoretical models of the climate have been. Even after accounting for differences in geography, ocean currents, and vegetation during these past episodes, paleoclimatologists realized that an important but unknown factor was missing from their models.
Now, a new study in the scientific journal Nature Geoscience indicates that hitherto unknown factor is cloud cover. According to the study, decks of stratocumulus clouds, which cover about 20 percent of the low-latitude oceans, become unstable and break up into scattered clouds when CO2 levels rise above 1,200 parts per million.
This instability triggers a surface warming of a stunning 8 degrees Celsius globally.
For The Real News Network, I spoke to a co-author of the study, Professor Tapio Schneider. Our discussion can be watched and listened to here: