In order to predict our climate future, scientists spend a lot of time looking into the past, trying to understand what conditions were like during times when the planet was much warmer or much cooler than it is today. The latest instance: a report published in the February issue of the journal Geosphere, offering a plausible explanation for swings between long stretches of greenhouse warming and dramatic cooling over millions of years.
The culprit, said lead author Cin-Ty Lee of Rice University in an interview, appears to be the ebb and flow of eruptions from volcanic mountain chains around the globe, which alternately pump heat-trapping carbon dioxide into the atmosphere and allow it to be re-absorbed by rocks and living things.
While these changes happen far too slowly to have any bearing on the current, human-caused episode of global warming, they do help scientists to understand the relationship between carbon-dioxide concentrations in the atmosphere and global temperature changes.
The new idea is that it’s a more sustained series of eruptions from volcanoes in strategic locations along the edge of continents that cause these long periods of warmth.Credit: flickr/NASA’s Marshall Space Flight Center
The main effect of volcanoes in the modern world is to cool the planet by throwing particles of sulfur dioxide high into the stratosphere, where they temporarily block the Sun. In the distant past, however, paleo-climatologists have long believed that volcanic activity was a major cause of global warming. Massive eruptions — far more powerful than anything going on today — can pump large amounts of heat-trapping carbon dioxide into the air. The problem with that theory is that those events don’t last long enough to explain periods of warmer climate that have lasted tens of millions of years.
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