• Jacob Bourne

Space Mission to Explore Venus’ Runaway Hothouse Climate: Could it Happen on Earth?

NASA has announced that it will collaborate with the European Space Agency on its EnVision mission to the most mysterious planet this side of the asteroid belt.

Illustration of Venus. Credit: Shutterstock/Jurik Peter

The partnership involves NASA contributing VenSAR technology, courtesy of the Jet Propulsion Laboratory. VenSAR is a synthetic aperture radar that will enable high-resolution measurements of Venus’s surface features. The mission's focus is on making observations of the planet to better understand its atmospheric and geologic processes through higher resolution images than were possible in the past.

With a surface temperature of about 867 degrees Fahrenheit and shrouded in a thick, high-pressure atmosphere made of 96.5% carbon dioxide, observations are a bit tricker than on Mars with its thin atmosphere and much colder surface temperature. In other words, space agencies can’t just drop a rover to go off-roading on Venus like on Mars, though the Soviet Union did land several crafts on Venus between 1970 and 1982, all succumbing to the extreme conditions within two hours or less.

“High-resolution images of many dynamic processes at Mars profoundly changed the way we thought about the Red Planet, and images at similar scales have the potential to do the same for Venus,” said Lori Glaze, director of NASA’s Planetary Science Division.

EnVision coincides with NASA’s other two Venus missions, DAVINCI+ (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging) and VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy).

“The combined results of EnVision and our Discovery missions will tell us how the forces of volcanism, tectonics, and chemical weathering joined together to create and sustain Venus’ runaway hothouse climate,” said Tom Wagner, NASA’s Discovery Program scientist at NASA Headquarters.

A greater understanding of Venus’ climate is of particular interest. Scientists postulate that billions of years ago, Venus was Earth-like in its atmospheric composition but eventually transformed into an inferno through a runaway greenhouse effect triggered by the sun’s energy.

Credit: European Space Agency / Paris Observatory / VR2Planets

When a planet’s atmosphere contains high greenhouse gas concentrations, solar radiation is trapped close to the surface. If the planet has liquid water, then the added heat triggers evaporation. Because water vapor is itself a greenhouse gas, the elevated amounts gained through evaporation, in turn, trigger more heating, which in turn trigger more evaporation, and on and on until the oceans are boiled into the sky, rendering a much less hospitable planet — at least for life as we know it.

The greenhouse effect is in full swing on Earth. Anthropogenic climate change was triggered by centuries of fossil fuel burning, causing elevated amounts of carbon dioxide and other greenhouse gases like methane and nitrous oxide to warm the planet. The water vapor factor is also at play alongside other positive feedback loops like the loss of the albedo effect in the Arctic and greenhouse gases released from melting permafrost.

It’s unclear at what exact point the greenhouse effect becomes the runaway greenhouse effect, though boiling oceans would be a telltale sign of the latter. The Earth’s oceans may not be boiling, but reports from field scientists of methane bubbling at the surface of Arctic lakes visually reminiscent of a boil are disturbingly suggestive.

In 2018, NASA scientists assessed the possibility of a runaway scenario on Earth. The conclusion was that a couple thousand parts per million of CO2 or a large burst of methane would be necessary to trigger such a tumultuous process, not the latest reading of 419.34 ppm from the Mauna Loa Observatory. Yet, the assessment revealed a phenomenon called the super greenhouse effect underway in Earth's tropical regions where the warming feedback loop is “super-powered” by the churning of large volumes of water vapor upward by high altitude storms. Not only did NASA scientists say that the SGE causes intensified warming locally, but that a similar mechanism was probably involved in Venus’ fate long ago.

Regarding the large burst of methane needed to trigger runaway, one certainly hasn’t happened yet, or it would be apparent given that methane’s warming potential is fast-acting compared to CO2. However, dozens of news reports from The Siberian Times indicate that such a risk is at least a possibility.

The scientific commentary to date on whether runaway greenhouse is possible on Earth keeps the status of the question open. Yet, the relevance of the question is relative. The future of the planet itself would be irrevocably impacted by runaway. Still, the complex organisms that inhabit it would likely be wiped out long before the oceans simmered.

The Earth is already losing species at a rate between 1,000 and 10,000 times higher than the natural extinction rate, though climate change isn’t the sole anthropogenic cause.

The runaway scenario is not entirely ruled out as a possibility because the current rate of CO2 concentration rise in the atmosphere is unprecedented. According to Scripps Institution of Oceanography, an increase in 10 ppm of atmospheric CO2 might have taken 1,000 or more years to accumulate in Earth’s past. However, the 1,000 ppm threshold could be reached in just 100 years under a high emissions scenario.

Back to Venus. The upcoming missions to Earth’s fiery sister provide an opportunity to more deeply understand what hopefully will not become an analog of our planet’s future. The greenhouse effect may seem simple, but Earth’s climate system is so complex that it’s hard for predictive modeling to grasp. It’s also noteworthy that space missions themselves create a blast of pollution at launch and carbon emissions associated with the production of hydrogen fuel, adding to the warming troubles. Hopefully, the trip will glean some beneficial knowledge that could offset the damage.


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