by Using advanced computer simulations, scientists have shown how easily a runaway greenhouse effect can quickly transform a habitable planet into a hellish world inhospitable to life.
This research not only has implications for our understanding of the extrasolar planets, or “exoplanet,” but also sheds light on the human-driven climate crisis on Earth.
The team of astronomers from the University of Geneva (UNIGE) and the CNRS laboratories in Paris and Bordeaux saw that, after the initial stages of the planet’s climate change, the planet’s atmosphere, structure and cloud cover are significantly altered, making it difficult stop it. A runaway effect begins to set in. It is alarming that this process could be initiated here on Earth with a small change in sunlight or a global temperature rise of a few ten degrees. Even these minor changes could make our planet completely inhospitable.
Therefore, the research gives a big warning about climate change.
“Until now, other key studies in climatology have focused entirely on the moderate state before the run or the habitable state after the run,” Martin Turbet, CNRS scientist and team member, said in a statement. “This is the first time a team has studied the transition itself with a 3D global climate model, and checked how the climate and atmosphere evolve during that process.”
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Critical greenhouse effect
The runaway greenhouse effect in the team’s simulation can see a planet change from having a temperate, Earth-like state to one that exhibits a hellish surface temperature of around 1,800 degrees Fahrenheit (1,000 degrees Celsius). That’s hot enough to melt lead. These temperatures are even higher than those on the surface of Earth’s hellish neighbor, Venus.
The cause of this runaway greenhouse effect is very familiar: Water vapor – a major greenhouse gas. Although water vapor may not be the first greenhouse gas we think of when it comes to global climate change, like more common greenhouse gases such as carbon dioxide and methane, water vapor stops the sun’s radiation being absorbed by the surface of the planet from escaping back into space. This traps heat around the world like a thermal blanket. Scientists call it the greenhouse effect.
In small doses, the greenhouse effect is useful; for example, it stops the Earth from showing temperatures below the freezing point of water. But too much greenhouse warming can force the oceans to evaporate, putting a lot of water vapor in the atmosphere. As you can imagine, this could lead to more greenhouse warming. It’s like a feedback loop. Aha, the “runaway” greenhouse gas effect.
Venus provides a stark example of what can happen when a greenhouse effect starts running.
“There is a critical threshold for this amount of water vapor, which cannot cool the planet any more,” said research leader and former University of Geneva Department of Astronomy scientist Guillaume Chaverot. From there, everything turns until the oceans become completely evaporated and the temperature reaches hundreds of degrees.”
Warning clouds
One of the most important and surprising features that emerged from the team’s simulation was the development of an odd cloud pattern. This pattern not only increased the runaway greenhouse effect but also produced it irreversiblee.
“From the beginning of the transition, we can observe some very dense clouds developing in the upper atmosphere,” said Chaverot. “Actually, the latter no longer shows the characteristic temperature inversion of the Earth’s atmosphere and separates its two main layers: the troposphere and the stratosphere. The structure of the atmosphere is greatly changed.”
As for what this means for us, with the results of the simulation in hand, the team calculated that it would only take a small increase in solar radiation and a rise of ten degrees in Earth’s temperature to trigger an apocalyptic runaway effect. If that happened, Earth would be as hostile to life as its neighbor Venus is right now.
The news comes as countries seek to limit human-driven greenhouse gases to limit overall global warming to 1.5 degrees Celsius by 2050, showing just how critical this effort really is.
The team is still unsure about the effect that the release of greenhouse gases alone might have on the process that went away and whether that process can “go away” at the same temperatures. They have yet to find out if increasing solar luminosity could continue to drive the process.
“Assuming that this runaway process started on Earth, the evaporation of only 10 meters of the ocean’s surface would result in an increase of 1 bar in atmospheric pressure at ground level,” said Chaverot. “In a few hundred years, we would reach the temperature of the earth over 500 degrees Celsius. Later, we would even reach 273 bar surface pressure and over 1,500 degrees Celsius, when all the oceans completely evaporated.”
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The research is also extremely important as humanity becomes more capable of seeing and studying the planets around other stars, a scientific discipline that will lead us to hunt for life outside the solar system.
“By studying the climate on other planets, one of our strongest motivations is to determine their potential to host life,” said staff member and director of the University of Geneva Life in the Universe Center (LUC ) Émeline Bolmont. “After the previous studies, we already suspected that there was a water vapor threshold, but the appearance of this cloud pattern is a real surprise!”
The team’s research was published on December 18 in the journal Astronomy & Astrophysics.
