It could become another Venus:
The “runaway greenhouse” — which is thought to have happened on Venus in the past — is basically a climate change worst-case scenario: We reach a critical point where the atmosphere is so thick with greenhouse gases that no sunlight can escape back into space, the planet heats uncontrollably, the oceans evaporate completely, and things get, well, pretty uncomfortable, to put it mildly. “Everything is really quite dead at that point,” Colin Goldblatt, a planetary scientist at Canada’s University of Victoria, says in a chipper English accent. Goldblatt has been working to understand whether a runaway greenhouse could ever happen on Earth.
Scientists have long believed that even with extreme greenhouse gas concentrations, our sun simply doesn’t heat the planet enough to trigger this effect. But using a series of custom computer programs that model incoming sunlight, greenhouse gas concentration, radiation absorbed by water vapor, and a host of other physical factors, Goldblatt has revised that threshold down, and in a paper published Sunday in Nature Geoscience says that a runaway greenhouse could kick off with the amount of sunlight we get today.
Clouds act as Earth’s saving grace:
So, what’s keeping us cool? The [paper’s] authors suggest two things. The first is that our atmosphere isn’t uniformly saturated with water; some areas are less humid and allow more heat to radiate out into space. The other factor is the existence of clouds. Depending on their properties, clouds can either insulate or reflect sunlight back into space. On balance, however, it appears they are key to keeping our planet’s climate moderate.
But clouds won’t help us out indefinitely. Long before the Sun expands and swallows the Earth, the amount of light it emits will rise enough to make a runaway greenhouse more likely. The authors estimate that, with an all-water atmosphere, we’ve got about 1.5 billion years until the Earth is sterilized by skyrocketing temperatures. If other greenhouse gasses are present, then that day will come even sooner.
(Image of Venus via Wikimedia Commons)
The Dish 
