Why haven't we encountered alien life? It was killed off by climate change, new study suggests

Report's findings offer glimpse of a grim future for Earth if attempts to curb global warming fall short

Scientists suggest we have not encountered alien civilisations because they have been wiped out by climate change on their planets. EPA

Are we alone in the universe? It remains one of the great unanswered questions of our age. Alien civilisations on other planets sound like the stuff of Hollywood blockbusters or science fiction novels, but a new study could offer a glimpse into why we have never encountered one.

It seems implausible that in a universe so vast that we should be the sole intelligent society. Which raises an obvious issue, why have we not uncovered the existence of extraterrestrial life anywhere in the cosmos by now?

A new study suggests that could be because they are too busy causing their own demise by heating up their planets through vast energy consumption. The study's findings offer a glimpse of a potentially grim future for Earth, should efforts to tackle climate change fall short.

They suggest that civilisations consuming similar amounts of energy to us would find their planets uninhabitable after a certain period, estimated be no longer than 1,000 years – even without burning fossil fuels.

The findings are “a bit of a shock”, says study co-author Dr Amedeo Balbi, an associate professor of astronomy and astrophysics at the University of Rome Tor Vergata.

“You have these results that were a bit surprising to ourselves, that only a few centuries will increase the temperature of the planet beyond the level at which it will be habitable,” he said.

“If you have this kind of exponential growth anywhere, it’s not, by definition, something that can last forever. Eventually everything will increase faster than any system will tolerate.”

Alone in the universe?

He said that might help to explain why, despite looking very hard with increasingly sophisticated technology, humans have yet to discover any other technological society, or even any other form of life, beyond planet Earth.

In previous generations there was what he described as “a lot of optimism” about finding other civilisations and a hope that we could become part of a “galactic club”.

“The fact of the matter is we haven’t found any evidence of that. When we look outside and look at the universe, it’s very silent,” Dr Balbi said. “Either they’re very well hidden or we haven’t looked very well, but that’s not true: we’ve been looking for quite a long time now.”

This could be because intelligent life is rare and it is hard to “climb the ladder of technological progress”. Or it could be because societies have continued to grow at an unsustainable rate.

“In either case, the humbling answer is there are probably not many old, long-lived technological civilisations out there,” he said.

Using complex mathematical calculations, the researchers determined the heating effect, and its impact on habitability when energy demand increased by one per cent annually. Last year electricity demand on Earth rose 2.5 per cent, according to the International Energy Agency.

“Our analysis suggests that, if the energy growth rate is of the order of one per cent per year, the maximal lifetime of such putative technospheres is ephemeral compared to stellar evolution,” the researchers wrote.

“Significant heating – which can drive the planet beyond potentially dangerous thresholds – due to exponential waste heat generation is predicted to occur on a short timescale of [less than or equal to] 1,000 years.”

The key issue is that when one form of energy is converted to another, some of that energy is dissipated or lost as heat, even if great efforts are made to avoid this loss.

“Whatever energy you use, there’s no way you can avoid producing waste heat, because that’s what the principles of thermodynamics tell us,” Dr Balbi said. “When you convert energy to do work, like using machines or electricity or whatever kind of conversion you do, eventually a fraction of this energy will be degraded and converted into heat and go into the environment.

“There are basic limits that tell you [that] you will never reach a perfect efficiency, you will never build a perfect engine. You will never convert all of the energy that you use into usable energy. You will always have some waste heat.”

To take an example on Earth, even an electric vehicle powered by renewable energy generates heat, such as in its tyres or its brakes. The heat generated by energy conversion ends up in the planet’s atmosphere and, while some will be lost to space, if the heat generation continues, as will be the case in growing societies, there will be planetary warming.

Is our fate sealed?

However, the research, which was co-authored by Dr Manasvi Lingam, of the Florida Institute of Technology, also suggests that if civilisations exist in a steady state instead of continuing to grow, their demise within hundreds of years is no longer inevitable.

“Maybe this kind of exponential growth that our civilisation, our society kept for the past few decades or century is not sustainable in the long term,” Dr Balbi said.

“Maybe one answer is to rethink the way we use energy or the way we grow. But there may be other answers that go in a different direction that are preferable for other people.

“One answer could be we just have to move elsewhere and transfer all our production and all our energy production and consumption somewhere else in space. Then we can keep growing and expanding for ever.”

Dr Balbi said that there were “reasons to be sceptical” about whether this would work, based on what is known about physics and the challenges of creating settlements away from Earth. But while he said he was unsure if humans could move elsewhere, it was a possibility.

“Maybe the solution will be in technological progress. We keep going and we find answers,” he said. “We have to have conversations about what’s best for our civilisation and for humanity in general.”

It could happen 'to any intelligent species'

Prof Peter Vickers, co-director of the Centre for Humanities Engaging Science and Society at Durham University in the UK, researches issues around the search for alien life. He said he was “sympathetic” to the idea that any other technological society would not last long.

“There has been literature arguing this for a while, mostly based on our own case that what’s happening here on Earth would plausibly happen to any intelligent species – a runaway effect of using natural resources beyond the breaking point,” he said.

He said that there was a consensus that if alien life existed, it would have evolved under the same laws of nature as those found on Earth, sometimes described as survival of the fittest, resulting in organisms that “overindulge in what’s available”.

“The species that can use tools the best is often going to be the most successful species and that’s probably going to be the case on any planet,” he said.

“Using tools leads to using technologies, which leads to extracting natural resources, which leads to, if you like, ruining your home.

“At some point they have to ask themselves 'are we overdoing it' and then it’s going to be really hard to go back on the track they’re on, because extracting natural resources brings such benefits in the short term.”