New Studies Reveal Climate Extremes from Fire to Ice

Climate scientists don't just rely on computer models and contemporary observations to understand the intimate relationship between CO2 in the atmosphere and environmental conditions on Earth.  They also look to the ancient past — and two reports in recent days have made it clear how intimate that relationship is.  One chronicles an episode 2.4 billion years in the past, when the entire planet was covered in a layer of ice hundreds of feet thick, oceans and all, while global average temperatures hovered around 40° F below zero.

A massive infusion of heat-trapping CO2 from powerful volcanoes — more CO2 than we're likely to emit in many hundreds of years, to be sure — saved the planet from this so-called Snowball Earth environment.  The second report covers an event that happened about 250 million years ago, and this time the effects weren't so benign.  Another set of gigantic eruptions poured enough CO2 into the air not only to warm the planet drastically, but also to acidify the oceans so profoundly that some 90 percent of all ocean species died off, followed by two-thirds of land species.  It's the worst mass extinction, as far as we know, in history.

These monumental episodes of climate change, both linked intimately to levels of CO2 in the atmosphere, are a testament to the dramatic effects this greenhouse gas has on the entire planet.  So it's no surprise that the smaller amounts we're emitting could have a significant effect as well.

The first of the new papers was published in the Proceedings of the National Academy of Sciences and the second in Science.

During the older episode, continental drift had brought most of the continents near the equator, where CO2, washed out of the atmosphere by rain, reacted chemically with exposed rock and was no longer available to trap heat from the Sun.  The global cooling that resulted let sea ice expand until it reached well into what would are now the planet’s temperate zones.  At that point, the dazzlingly white surface of the ice would have reflected enough sunlight back into space to accelerate the cooling — just the opposite of the so-called ice-albedo feedback in which diminishing Arctic ice coverage is speeding warming in the region.

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