Runaway Greenhouse Effect - Distant Future

Distant Future

Most scientists believe that a runaway greenhouse effect is actually inevitable in the long term as the Sun gradually gets bigger and hotter as it ages. Such will potentially spell the end of all life on Earth. As the Sun becomes 10% brighter in about one billion years' time, the surface temperature of Earth will reach 47 °C (117 °F), causing the temperature of Earth to rise rapidly until it becomes a greenhouse planet similar to Venus today. This will be the single most dramatic step in annihilating all life on Earth. According to astrobiologists Peter Ward and Donald Brownlee in their book The Life and Death of Planet Earth, (most of this is discussed in this book's Chapter 8) the current loss rate is approximately one meter of ocean per billion years, but this rate is gradually accelerating as the sun gets warmer, to perhaps as fast as one meter every million years. Ward and Brownlee predict that there will be two variations of this future warming feedback: the "moist greenhouse" where the oceans are lost relatively quickly, perhaps by one billion years' time, allowing some microbial life to survive on Earth until the Sun becomes a red giant, and the "runaway greenhouse" where the oceans are lost too slow that the Earth starts to undergo rapid warming that could send its surface temperature over 900 °C (1,650 °F) as the atmosphere will be totally overwhelmed by water vapor, causing its entire surface to melt and killing all life, perhaps in about three billion years' time. Either way, the loss of oceans will inevitably turn the Earth into a primarily desert world with the only water left being a few evaporating ponds scattered near the poles, and huge salt flats around what was once the ocean floor, much like the Atacama Desert in Chile, where the last life may remain for a few billion more years. Ironically, because of this the loss of oceans will actually save the last life instead of destroy it completely. The loss of oceans will also cause plate tectonics to come to a halt, since seawater naturally serves as a lubricant for plate tectonics, and hence tectonic activity cannot occur without water. Once plate tectonics stop, all life will still disappear from the Earth since with it the carbon cycle will also stop since plate tectonics constantly recycle carbon dioxide. However, by then all complex life including all plants and animals will be long extinct from the planet.