When Earth's Oceans Boil: New Climate Model Reveals Runaway Warming

Solar luminosity is slowly increasing over time, a process that actually has nothing to do with current climate warming. Yet over time, this increasing luminosity will cause Earth's temperatures to rise over the next few hundred million years. This, in turn, could result in the complete evaporation of the oceans. Now, scientists have created the first three-dimensional climate model that predicts exactly when liquid water will disappear from Earth.

Like most stars, the Sun's luminosity very slowly increases during the course of its existence. Due to this higher solar radiation, researchers expect that Earth's climate will become warmer over time--of the order of hundreds of millions of years. This is independent of human-induced climate warming, which can occur over decades. It's very possible that this long-term warming could actually cause a runaway warming scenario, similar to what happened on Venus, and cause the oceans to boil and entirely disappear. Just a little nearer to the Sun than Earth, Venus turned into a furnace in the distant past.

So when might this runaway warming state occur? Before now, it's been difficult to say exactly when this might happen. In order to better understand the far future of our planet, the researchers designed a three-dimensional model that's able to predict how the terrestrial environment will change under the effect of a significant increase in solar flux, causing evaporation of liquid water into the atmosphere. They found that the tipping point for runaway warming should occur when mean solar flux reaches approximately 375 W/m2 with a surface temperature of about 70 degrees Celsius. This, in particular, is set to occur in about one billion years.

So what will happen at this time? The oceans will start to boil and the greenhouse effect will increase until it enters a runaway state. The latest findings actually push back earlier predictions for the complete evaporation of the oceans by several hundred million years.

The findings don't just tell us more about our own Earth, though. They can also be used to determine the extent of the habitable zone around the Sun. They show that a planet can be as close as .95 astronomical units to a star similar to our Sun before losing all its liquid water. In addition, the research reveals that a planet does not need to be exactly like Earth to have oceans. This could help researchers detect habitable planets in the future.

The findings are published in the journal Nature.