The first generation of exoplanet-hunting space telescopes such as Kepler and COROT have revealed that the majority of stars in the galaxy host planets, which may mean that something on the order of a trillion planets exist in the universe. Although we haven’t heard from any extraterrestrials yet, the sheer abundance of planets means there’s pretty good odds that other intelligent civilizations have cropped up at some point in the last 13 billion years.
Some of these alien civilizations may have lasted long enough to develop sophisticated technologies like our own, which means they may have had to deal with some of the same problems we are currently dealing with on Earth, like how our energy-intensive civilizations fuel climate change. The question, then, is did these extraterrestrial civilizations survive their own success at harvesting energy?
Even though we don’t have any data on extraterrestrial civilizations just yet, answering this question isn’t hopeless. As detailed in a recent study published in Astrobiology, it is possible to create models of the development of extraterrestrial civilizations based on what we know about Earth and the other planets in our solar system.
The models developed by Adam Frank, an astrophysicist at the University of Rochester, and his colleagues look at two primary factors in the development of a technical civilization: population size and energy use. These two factors are deeply linked insofar as the ability to harness greater levels of energy means that we can sustain larger populations. Yet as population size balloons, this also results in feedback from the environment relative to the size of the population and the type of energy used.
For humans, which have mostly relied on fossil fuels for energy for the last 150 years, we call some of the detrimental feedback from our energy use climate change, yet the effects of our growing population can also be seen in the rapid depletion of the fossil fuels themselves. At a certain point, the effects of climate change can get so bad that they start to severely damage other things that are necessary for human existence. For example, soaring temperatures can kill crops, the changing climate can produce sustained drought, and rising sea levels can inundate coastal cities.
This type of planetary feedback has a negative effect on the human population. If it were to get bad enough, it could possibly wipe out humans entirely. Yet human intelligence also means that we have options—we can switch to renewable energy sources like solar power that have a far smaller impact on our planet. Whether such a switch will be too little, too late, however, remains an open question.
It was the interplay of these factors that Frank and his colleagues used to create their models of the possible fates of extraterrestrial civilizations. As Frank detailed in an article about his research in The Atlantic , their models revealed three main types of trajectories for alien civilizations. The most common one was called “the die off” and as its name suggests, it’s not a great outlook. In these models, civilizations grew so rapidly as they harnessed energy from fossil fuels that they soon exceeded their planet’s limits. This resulted in large numbers of the planet’s population dying until it reached a sustainable equilibrium.
“In many models, we saw as much as 70 percent of the population perish before a steady state was reached,” Frank wrote. “In reality, it’s not clear that a complex technological civilization like ours could survive such a catastrophe.”
The second possibility, which Frank described as the “soft landing,” saw populations transition to a clean energy regime as their size grew. This allowed them to achieve an equilibrium without losing most of their population.
Then there’s the third option, which is the total collapse of an extraterrestrial civilization. In these models, the host planet was too sensitive to sustain the rapid growth of an energy-intensive civilization that relied on fossil fuels and it led to the complete extinction of the extraterrestrial population. Although it seems like changing to a renewable energy could help stave off the apocalypse, Frank wrote that in some models, even a rapid transition to a clean energy regime couldn’t save the civilization—its demise was just delayed.
“In some of the ‘delayed collapse’ histories, the planet’s own internal machinery was the culprit,” Frank wrote. “Push a planet too hard, and it won’t return to where it began.”
This can happen even on planets where there was no civilization. In fact, many planetary scientists think that Venus was once quite Earth-like, but a runaway greenhouse effect turned it into the hellish planet we know today.
Read More: Exoplanets May Help Us Understand How Venus Turned Into a Hell Planet
Ultimately, these models of possible extraterrestrial civilizations tell us more about the future of our own planet than they do about any alien societies that may be lurking among the stars. They underscore the importance of studying the climate on our own planet in order to create more realistic physical models of planetary evolution. Doing so may determine whether our species has a future and will get to join the ranks of extraterrestrial civilizations that also figured out how to find equilibrium on their own planets.
“From that perspective, the true narrative of climate change isn’t some small, local drama of Democrats vs. Republicans, or business interests vs. environmentalists,” Frank wrote. “Instead, it’s a cosmic test, one that gives us a chance to join those who successfully crossed this burning frontier—or the chance to be consigned to the scrap heap of civilizations too shortsighted to take care of their own planet.”