A runaway greenhouse effect, in which a planet heats up uncontrollably and the oceans evaporate, may be easier to initiate than previously thought, reports a study published online this week in Nature Geoscience. A stable temperate climate (such as that enjoyed by Earth) and a runaway greenhouse effect are both possible outcomes for a planet that receives the same level of solar radiation as the Earth today. It was previously thought that the amount of solar radiation required for a runaway greenhouse effect was higher.
Colin Goldblatt and colleagues used numerical models to calculate the balance between solar radiation absorbed and thermal radiation emitted by the Earth’s surface and atmosphere. They find that a runaway greenhouse effect is possible for a planet receiving a similar amount of solar radiation as the Earth does today. Although more complex atmospheric models are still needed, they suggest that under certain atmospheric conditions - such as high levels of greenhouse gases and few clouds - a stable temperate Earth could transition to a runaway greenhouse state. However, the authors note that projected anthropogenic greenhouse gas emissions in the near future are insufficient to trigger such a runaway greenhouse effect on Earth.