Most planets inhabited by advanced civilisations would be likely to face catastrophic climate change as a result of burning fuel, researchers have found.

Human activity has had a geological impact on Earth, putting it into a new epoch known as the Anthropocene. Adam Frank at the University of Rochester, New York, and his colleagues wanted to know if the same thing might happen on other Earth-like planets.

The researchers began with the assumption that “exocivilisations” would arise on planets with initial carbon dioxide levels that weren’t detrimental to life forming and would at first generate energy through combustion to grow their population, just as humans have done. They also looked at whether a planet’s distance from its star would have an impact. “Essentially we asked, if Earth was moved, would civilisations still trigger a climate change,” says Frank.

Each planet was also assumed to have started with a temperature of around 14°C. Those closer to the star would receive more heat and so would begin with less CO₂ in their atmosphere, while further-away ones would begin with more.

The researchers used climate models to see what would happen to Earth-like planets within a star’s habitable zone – the region in which liquid water can exist on a planet’s surface – under these assumptions as the population grew. They found that around 60 per cent of such planets would undergo climate change caused by Anthropocene-like conditions, and population growth would be limited by the increase in temperature.

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This was more common on the low-carbon-atmosphere planets closer to their host star, which would have a higher climate sensitivity, a measure of how much the planet warms in reaction to changes in the levels of CO₂. The team found that even small CO₂ increases on these planets would be enough to trigger a climate change event that could harm the population.

For planets on the outer edge of a star’s habitable zone, which would begin with thicker CO₂ atmospheres, climate sensitivity would be lower and civilisations could drive CO₂ levels higher without affecting their population. The team found that these populations would reach the planet’s carrying capacity, growing to sizes that are unsustainable for the amount of resources on the planet, before climate change had a chance to take effect.

These findings suggest that inducing climate change would be a common problem for growing societies on any habitable planet. “Civilisations and planets work together,” says Frank. But Jim Kasting at Pennsylvania State University says we can’t assume that life on these planets would have the same heat-tolerance levels as humans do.

Frank says the research can also help us understand the climate situation here on Earth. “The question now is: do we drive the planet off a cliff, or do we drive the planet to safety?”

Reference:arxiv.‌org/abs/2103.06330