Using advanced computer simulations, scientists have shown how easily a runaway greenhouse effect can quickly transform a habitable planet into a hellish world incapable of life.
This research not only has implications for our understanding of extrasolar planets, or " exoplanets ", but it also offers insights into the Earth's man-made climate crisis.
The team of astronomers from the University of Geneva (UNIGE) and the CNRS laboratories of Paris and Bordeaux saw that after the first stages of a planet's climate transformation, the planet's atmosphere, structure and cloud cover change significantly, making a difficult to stop the runaway effect begins to manifest. Alarmingly, this process could be initiated here on Earth with just a small change in the sun's brightness or with a global average temperature increase of just a few tens of degrees. Even those small changes can lead to our planet becoming completely inhospitable.
The research therefore offers a clear warning about climate change.
"Until now, other major studies in climatology have focused exclusively on the temperate state before the runaway, or on the habitable state after the runaway," says Martin Turbet, scientist and CNRS team member. said in a statement. "It is the first time that a team has studied the transition itself with a global 3D climate model, and examined how the climate and atmosphere evolve during that process."
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The runaway greenhouse effect in the team's simulation could shift a planet from a temperate, Earth-like hospitable state to a hellscape state with surface temperatures of about 1,800 degrees Fahrenheit (1,000 degrees Celsius). That's hot enough to melt lead. These are temperatures even higher than those on the surface of Venus, Earth's famous hellish neighbor.
The cause of this runaway greenhouse effect is something very familiar: water vapor - a major greenhouse gas. While water vapor may not be the first greenhouse gas we think of when it comes to climate change on Earth, like better-known greenhouse gases like carbon dioxide and methane, water vapor keeps solar radiation absorbed by a planet's surface from escaping back into space . This traps heat around the world like a thermal blanket. Scientists call this the greenhouse effect.
In small doses, the greenhouse effect is useful; For example, it ensures that the Earth does not exhibit temperatures below the freezing point of water. But too much warming caused by global warming can force the oceans to evaporate, releasing a lot of water vapor into the atmosphere. As you might imagine, that could cause even more greenhouse gas warming. It's like a feedback loop. Ah, the 'runaway' greenhouse gas effect.
Venus is actually a striking example of what can happen when a runaway greenhouse effect takes hold.
"There is a critical threshold for this amount of water vapor, above which the planet can no longer cool," said Guillaume Chaverot, research leader and former astronomy scientist at the University of Geneva. From there everything gets carried away, until eventually the oceans evaporate completely and the temperature reaches several hundred degrees."
Warning clouds
One of the most important and surprising aspects to emerge from the team's simulation was the development of a strange cloud pattern. This pattern has not only amplified the runaway greenhouse effect, but also caused it irreversible e.
"From the beginning of the transition, we can observe some very dense clouds developing in the high atmosphere," Chaverot said. "In fact, the latter no longer shows the temperature inversion characteristic of the Earth's atmosphere and separates the two main layers: the troposphere and the stratosphere. The structure of the atmosphere has changed profoundly."
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 an increase in Earth's temperature by tens of degrees to trigger an apocalyptic runaway effect to bring about. If that were to happen, Earth would eventually become as hostile to life as its current neighbor Venus.
The news comes as countries seek to limit man-made greenhouse gases to limit overall global warming to 1.5 degrees Celsius by 2050, showing how important this effort really is.
The team is not yet sure of the effect that greenhouse gas emissions alone could have on the runaway process and whether that process can really just disappear at the same temperatures. They also have yet to discover whether an increase in solar brightness could continue to stimulate the process.
"Assuming this runaway process started on Earth, evaporation of just 10 meters from the ocean's surface would lead to a 1 bar increase in atmospheric pressure at ground level," Chaverot said. "Within a few hundred years we would reach a bottom temperature of more than 500 degrees Celsius. Later we would even reach a surface pressure of 273 bar and more than 1,500 degrees Celsius, while all the oceans would eventually evaporate completely."
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The research is also of great importance as humanity becomes increasingly adept at spotting and studying planets around other stars, a scientific discipline that will eventually lead us to look for life beyond the solar system.
"By studying the climate of other planets, one of our strongest motivations is to determine their potential to host life," said Émeline Bolmont, team member and director of the Life in the Universe Center (LUC) at the University of Geneva. "After the previous studies, we already suspected the existence of a water vapor threshold, but the appearance of this cloud pattern is a real surprise!"
The team's research was published in the journal on December 18 Astronomy and astrophysics.
