Researchers assert that the climate of exoplanets can easily transition from habitable to infernal.

The Earth, a captivating blue and green orb teeming with oceans and life, stands in stark contrast to Venus, a yellowish, barren sphere that is not only inhospitable but also sterile. Despite this disparity, the temperature difference between the two is minimal. A groundbreaking achievement by a team of astronomers from the University of Geneva (UNIGE), with the collaboration of CNRS laboratories in Paris and Bordeaux, marks the world’s first successful simulation of the entire runaway greenhouse process. This process can transform a planet’s climate from idyllic and conducive to life into an exceedingly harsh and hostile environment.

The scientists have demonstrated that from the initial stages of the process, significant changes occur in the atmospheric structure and cloud coverage. These changes lead to an almost unstoppable and highly intricate runaway greenhouse effect, making it challenging to reverse. On Earth, a slight increase in the sun’s luminosity resulting in a global average temperature rise of just a few tens of degrees could trigger this phenomenon, rendering our planet uninhabitable. These findings are detailed in the publication in Astronomy & Astrophysics.

The concept of a runaway greenhouse effect is not new. In this scenario, a planet transitions from a temperate state, resembling Earth, to an inferno with surface temperatures exceeding 1,000°C. The culprit? Water vapor, a natural greenhouse gas. Water vapor acts like a thermal blanket, preventing solar irradiation absorbed by Earth from being reemitted into space. A modest greenhouse effect is beneficial, maintaining Earth’s average temperature above the freezing point of water and fostering conditions conducive to life.

Conversely, an excessive greenhouse effect accelerates ocean evaporation, increasing water vapor in the atmosphere. Guillaume Chaverot, former postdoctoral scholar in the Department of Astronomy at the UNIGE Faculty of Science and the study’s main author, explains that there is a critical threshold for the amount of water vapor, beyond which the planet cannot cool down. This leads to an escalating scenario where oceans fully evaporate, and temperatures soar to several hundred degrees.

Martin Turbet, a researcher at CNRS laboratories in Paris and Bordeaux and co-author of the study, highlights the unique aspect of their research. Unlike previous climatology studies that focused solely on either the temperate state before the runaway or the inhabitable state post-runaway, their team studied the transition itself using a 3D global climate model. They observed how the climate and atmosphere evolve during this intricate process.

A key aspect of the study is the emergence of a distinct cloud pattern that amplifies the runaway effect, rendering the process irreversible. Chaverot notes the development of dense clouds in the high atmosphere from the onset of the transition. The atmosphere loses its characteristic temperature inversion, which separates the troposphere and the stratosphere, signaling a profound alteration in its structure.

Serious consequences for the search of life elsewhere

This breakthrough holds significant importance for investigating the climates of other planets, particularly exoplanets—those orbiting stars other than the sun. Émeline Bolmont, assistant professor and director of the UNIGE Life in the Universe Center (LUC), and co-author of the study, emphasizes the motivation behind studying the climates of other planets: determining their potential to support life.

The LUC spearheads cutting-edge interdisciplinary research projects delving into the origins of life on Earth and the search for life within our solar system and beyond, in exoplanetary systems. Bolmont notes, “Following previous studies, we already suspected the existence of a water vapor threshold, but the revelation of this cloud pattern is truly unexpected.”

“In tandem, we have explored how this cloud pattern could generate a distinctive signature or ‘fingerprint’ that may be detectable when observing exoplanet atmospheres. The next generation of instruments should have the capability to identify it,” says Turbet. The team’s ambitions extend beyond this achievement, with Chaverot securing a research grant to advance the study at the “Institut de Planétologie et d’Astrophysique de Grenoble” (IPAG). This next phase of the research will focus specifically on the Earth’s case.

A planet Earth in a fragile equilibrium

Utilizing their novel climate models, scientists have computed that a slight elevation in solar irradiation—resulting in a global temperature increase of just a few tens of degrees—could initiate an irreversible runaway process on Earth, rendering our planet as inhospitable as Venus.

In the current pursuit of climate objectives, the aim is to restrict global warming on Earth, induced by greenhouse gases, to a mere 1.5 degrees by 2050. One aspect under investigation in Chaverot’s research grant is whether greenhouse gases can instigate the runaway process akin to the impact of a slight increase in solar luminosity. If so, the subsequent inquiry would involve determining if the threshold temperatures for both processes are identical.

The realization emerges that Earth is not distant from this apocalyptic scenario. “Supposing this runaway process were initiated on Earth, the evaporation of a mere 10 meters of the oceans’ surface would result in a 1 bar increase in atmospheric pressure at ground level. Within just a few hundred years, we would witness a ground temperature exceeding 500°C. Subsequently, surface pressure would escalate to 273 bars, and temperatures would surpass 1,500°C, culminating in the complete evaporation of all oceans,” concludes Chaverot.

This article is republished from PhysORG under a Creative Commons license. Read the original article.

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