Earth's Hellish Potential

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It used to be that Venus was the only planet in the solar system thought capable of a runaway greenhouse effect — hence its furnace-like inhabitability. But new modeling suggests that Earth is perfectly capable of falling into a self-reinforcing heating cycle as well. Luckily, not even humanity’s greenhouse gas emissions are enough to trigger that planet-killing scenario on our home planet.

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Just to review, a runaway greenhouse effect is where a planet gets stuck in a vicious cycle of heating and can’t stop. We’re not talking the anthropogenic kind of heating, of a few degrees Celsius. That kind of greenhouse heating is bad enough, but a runaway greenhouse effect would dry up the oceans and turn Earth into an autoclave: sterilized of life.

It’s long been thought that such a deadly cycle of heating was not possible on Earth because Earth is just far enough away from the Sun that our planet’s intake of solar energy is too low. But a paper in the July 28 issue of Nature Geoscience suggests Earth is close enough to the Sun after all.

Computer modelling by the University of Victoria’s Colin Goldblatt and colleagues shows that a planet that gets the same amount of solar irradiation as Earth could go either way: to a stable climate or a Venus-like disaster.

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The numerical model calculated the balance between solar radiation taken in and thermal radiation released back into space by Earth’s surface and atmosphere. They found that with a lot more greenhouse gases and steamy air Earth could morph into another Venus.

“A runaway greenhouse could in theory be triggered by increased greenhouse forcing, but anthropogenic emissions are probably insufficient,” the researchers write.

On the other hand, they do hope that their work helps to identify exoplanets that are in habitable zones of their stars, and are likely to have avoided runaway greenhouses, since, those are the best places to expect life.

The full paper is available online here.

IMAGE: The baked, lifeless surface of Venus is the result of a runaway greenhouse effect. New research shows that Earth is not so away from the Sun that it can’t get just as hellish, given the right atmospheric ingredients. Credit: NASA