What is the Runaway Greenhouse Effect?

Frozen Planet
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Four and a half billion years ago, Venus was considered to be a habitable planet. A habitable planet is a planet that can contain liquid water on its surface. However, Venus is far from habitable. Venus experienced a rapid change in its atmosphere as a result of a phenomenon called runaway greenhouse effect. This released huge amounts of carbon dioxide, a thick smog and massive sulfuric acid clouds. This also caused high pressures which are only experienced at the bottom of oceans on Earth.

The surface of Venus
The surface of Venus, which was once considered to be a habitable planet

What is runaway greenhouse effect?

A runaway greenhouse effect is essentially what comes after the point of no return. It occurs when positive feedback loops increases the amount of greenhouse gases in our atmosphere exponentially.

The process is started by an increase surface-water being evaporated. Water vapour is one of the most dangerous greenhouse gases because it is very effective at reflecting radiation back towards the Earth’s. This results in a rise in surface temperature, which causes more water to evaporate, accelerating the process.

This an example of a positive feedback loop. There are many positive feedback loops similar to this one which are perpetuating climate change such as melting the ice on earth, decreasing the amount of light reflected. This increases the amount of light absorbed on the earth, so the global temperature rises.

How significant is the threat to earth?

Runaway greenhouse effect scenarios on Earth are highly speculative. We know that we are not near this effect at the moment. In order for this to occur, we would need a significant amount of carbon dioxide or methane to be released. Based on our current emission projections, this is unlikely in the near future. Dr. Kahn from NASA says “You basically need CO2 levels of a couple thousand parts per million, of which we recently passed 400 parts per million, or a massive release of methane, and there’s really no evidence for that at this time.”

We measure the carbon in our atmosphere by parts per million (ppm). 10,000 years ago our carbon parts per million was 200 parts per million. Since we have only increased by 200 parts per million in the past 10,000 years, it is unlikely we will reach levels high enough for this in the near future.

The greenhouse effect is essential for our survival. Without the greenhouse effect, Earth’s surface would be -17°C and there would be no life on Earth. You can learn more about this on our article about the greenhouse effect. The Earth is rare in its conditions that allow life and it is essential that we preserve the conditions in order to preserve life. Although we are still far from the runaway greenhouse effect we are still imposing massive dangers onto ourselves by not fiercely regulating CO2 emissions. You can learn how to reduce your personal carbon footprint by taking our carbon footprint calculator.

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