Now, new findings reported today in the journal Nature Geoscience make the case that the effects of cloud loss are dramatic enough to explain ancient warming episodes like the PETM - and to precipitate future disaster. This feedback loop causes warming to spiral out of control.ДЇor decades, rough calculations have suggested that cloud loss could significantly impact climate, but this concern remained speculative until the last few years, when observations and simulations of clouds improved to the point where researchers could amass convincing evidence. With fewer white surfaces reflecting sunlight back to space, the Earth gets even warmer, leading to more cloud loss. But computer simulations of clouds have begun to suggest that as the Earth warms, clouds become scarcer. вЂњItвЂ™s quite clear at this point that the answer is clouds,вЂќ said Matt Huber, a paleoclimate modeler at Purdue University.Д¬louds currently cover about two-thirds of the planet at any moment.

Even after accounting for differences in geography, ocean currents and vegetation during these past episodes, paleoclimatologists find that something big appears to be missing from their models - an X-factor whose wild swings leave no trace in the fossil record.Д®vidence is mounting in favor of the answer that experts have long suspected but have only recently been capable of exploring in detail. Ancient warming episodes like the PETM were always far more extreme than theoretical models of the climate suggest they should have been. When the planet got hot, it got really hot. The PETM doesnвЂ™t only provide a past example of CO 2-driven climate change scientists say it also points to an unknown factor that has an outsize influence on EarthвЂ™s climate. As Kennett put it, вЂњEarth was triggered, and all hell broke loose.вЂќ Violent storms ravaged the planet the geologic record indicates flash floods and protracted droughts. The mammals also miniaturized over generations, as leaves became less nutritious in the carbonaceous air.

On land, primitive monkeys, horses and other early mammals marched northward, following vegetation to higher latitudes. The ocean turned jacuzzi-hot near the equator and experienced mass extinctions worldwide. 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 6 degrees. A picture emerged of a brief, cataclysmic hot spell 56 million years ago, now known as the Paleocene-Eocene Thermal Maximum (PETM). More data points surfaced in China, then Europe, then all over. The prehistoric mammal had also been breathing CO 2-flooded air. In 1992, the finder of the tooth fossil, Phil Gingerich, and collaborators Jim Zachos and Paul Koch reported the same isotope anomalies in its enamel that Kennett and Stott had presented in their ocean findings a year earlier. While those 17 kinds of plankton were sinking through the warming waters and settling on the Antarctic seabed, a tapir-like creature died in what is now Wyoming, depositing a tooth in a bright-red layer of sedimentary rock coursing through the badlands of the Bighorn Basin.

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