December 17, 2013
Climate Model Predicts Earth Will Lose Its Oceans In A Billion Years
[ Watch the Video: The Sun Will Evaporate Our Oceans Eventually ]
Ranjini Raghunath for redOrbit.com - Your Universe Online
One billion years from now, all the water on Earth could disappear, making it barren like Venus, and the culprit isn’t climate change. It’s the Sun, according to a new study published in the journal Nature.
Scientists have previously predicted that, even without climate change, the Earth’s surface would still heat up, because of the Sun’s increasing brightness. The difference is that the effects of climate change can be seen in decades, while the latter would be spread over millions of years.
The Sun’s brightness (measured by the total energy it gives off) has been increasing since it was born 4.5 billion years ago - about 7 percent every billion years.
As the Sun grows brighter, more and more water gets evaporated from the Earth’s oceans. Water vapor, like carbon dioxide, is a greenhouse gas that heats up the Earth’s surface, leading to more evaporation. This vicious cycle of heating and evaporation will keep increasing until it reaches a “runaway” state - a point of no return.
Scientists believe it was these conditions that drove Venus to its current, barren, furnace-like state. They also believe that, in another 4 billion years, the Sun’s brightness will have increased by 60 percent, possibly making Earth “roasted to bare rock.”
So far, scientists have struggled to estimate the tipping point when global warming would reach this runaway state. Some climate models have predicted that the tipping point could happen much earlier - in 150 million years from now. However, such models fail to take into account the effect of seasons or clouds on the Earth’s temperature.
But a new and improved 3D climate model has been developed by researchers at the Laboratoire de Météorologie Dynamique, at the Institut Pierre-Simon Laplace in France. This model shows that the runaway state would happen when Sun’s brightness hits a much higher threshold than previously estimated, and the Earth’s surface temperature hits 70 degree Celsius - about a billion years from now.
The model was designed specifically to measure how the Earth and Earth-like planets respond to the Sun’s increased brightness in extremely hot and moist atmospheres, the researchers wrote.
What made the difference? It turns out that, even if clouds end up losing their cooling “parasol” effect on the Earth’s surface, circulating air patterns called Hadley cells would come to the rescue. They would help reduce warming in vulnerable areas where it is most likely to go into a runaway state. The effects of these air patterns would help stabilize the climate even as the Sun’s energy increases, and help push the tipping point forward millions of years.
The model also predicts that an Earth-like planet can be closer to a Sun-like star than previously suggested - about 0.95 astronomical units, or 5 percent less than the Earth’s distance from the Sun - without losing all its water.
These findings provide insight on how the earth’s atmosphere is evolving and help scientists predict what conditions are needed for Earth-like planets to hold water on their surface, the researchers believe.
Image 2 (below): Numerical simulations of the Earth's surface temperatures at the spring equinox, with an increasingly luminous Sun in the future. The first two diagrams are obtained with the global climate model. The second one shows the situation just before the complete evaporation of the oceans. The last one (380 W/m2) is an extrapolation showing temperatures after the complete evaporation of the oceans. The dates, expressed in Myr (millions of years), indicate the Sun's evolution: in reality, the continents and topography will be totally different in this distant future. Credit: Jérémy Leconte