It's hard to assess the sustainability of our civilization when climate scientists and ecologists have nothing to compare ourselves to. Which is why we need to learn from the success — and potential failures — of distant alien civilizations.

It's an open question as to whether or not climate change poses an existential risk to the human species, but it's not looking good. We are poised to enter into the Anthropocene Era — an epoch in which our species becomes a powerful force of nature unto itself. Regrettably, we appear to be a force that's imposing more environmental harm than good.

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Detrimental changes to the planetary system include the depletion of natural fisheries, the loss of freshwater and rain forest habitat, and the continuing acidification of the oceans. Frighteningly, ongoing climate change could result in problematic disruptions to ocean currents, leading to superstorms and megadroughts. Worse, there's the potential for atmospheric feedbacks to occur and the onset of a runaway greenhouse effect.

Taken together, it could all trigger the collapse of human civilization. Trouble is, we're not entire sure how to resolve the situation. Some call for international treaties, while others say industrial and technological development should continue apace.

But what if we could study other civilizations — alien civilizations — who have already dealt with these problems? This is the proposal of two astrophysicists who say such questions could be answered by studying emerging data about Earth and other planets in our galaxy — and by combining the earth-based science of sustainability with the space-oriented field of astrobiology.

We Are Not Alone

"We have no idea how long a technological civilization like our own can last," says astrophysicist Adam Frank in a University of Rochester release. "Is it 200 years, 500 years or 50,000 years? Answering this question is at the root of all our concerns about the sustainability of human society."

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Indeed, it's highly unlikely that we're the first and only technologically-intensive civilization in the entire history of the galaxy. Consequently, Frank, along with his co-author Woodruff Sullivan, posit the suggestion that we could potentially learn some very important things about ourselves and our future by studying the past successes and failures of extraterrestrial intelligences (ETIs). In their new paper, which appears in the journal Anthropocene, they call for the creation of a new research program to answer such questions about our future — but one that's in a broad, astronomical context. Our current predicament, they argue, may be a natural or generic consequence of certain evolutionary pathways.

The trick, say the authors, is to identify the pathways for success.

Bring on Drake

Frank and Sullivan start their analysis by considering the famous Drake Equation, a formula used to estimate the number of ETIs in the universe. One of the most challenging aspects of the formula is in estimating the lifespan of communications-capable civilizations. For their analysis, the researchers concentrated on the average lifetime of a species with Energy-Intensive Technology, or SWEIT. After crunching the numbers, they figured that even if the chances of forming such a "high tech" species are 1 in a 1,000 trillion, there should still be 1,000 occurrences of advanced life like our own in the "local" region of the cosmos.

"That's enough to start thinking about statistics," says Frank, "like what is the average lifetime of a species that starts harvesting energy efficiently and uses it to develop high technology."

Mapping Trajectories

Using dynamical systems theory, the researchers mapped out a strategy for modeling the trajectories of various SWEITs over the course of their evolution. Not surprisingly, it shows how the developmental paths are strongly tied to interactions between the species and its host planet. For example, as the population of a technological alien civilization grows, so does its need to harvest energy. Consequently, the composition of the planet and its atmosphere changes over the course of certain timescales.

Schematic of two classes of trajectories in SWEIT solution space. Red line shows a trajectory representing population collapse. Blue line shows a trajectory representing sustainability. Credit: Michael Osadciw/University of Rochester.

As noted by the authors in the study:

Each SWEIT's history defines a trajectory in a multi-dimensional solution space with axes representing quantities such as energy consumption rates, population and planetary systems forcing from causes both "natural" and driven by the SWEIT itself. Using dynamical systems theory, these trajectories can be mathematically modeled in order to understand, on the astrobiology side, the histories and mean properties of the ensemble of SWEITs, as well as, on the sustainability science side, our own options today to achieve a viable and desirable future.

It's important, therefore, for astrobiologists to study all aspects of potentially habitable exoplanets. And in fact, astrobiologists are already starting to do this. Remote sensing of exoplanets via spectroscopic imaging can tell us about the atmospheric content of distant planets. These signatures could tell us, for example, if a civilization is spewing out levels of greenhouse gases at "unnatural" levels. Should we cast enough of a wide net, we might actually be able to start collecting data about planets that are inhabited — or were inhabited — by SWEITs.

Indeed, these surveys could yield important lessons for sustaining the civilization we've got right here on Earth. Sustainability, when used in an astrobiological context, thus becomes a location-specific tool within habitability studies as a whole (habitability and sustainability are very different things). Sustainability is concerned with a particular form of life on a particular planet, but astrobiologists want to know about all forms of life on all types of planets — and for all time.

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Of course, we're not entirely sure what alien life would look like, but the researchers say it doesn't matter. What's important are the sustainability models.

"If they use energy to produce work, they're generating entropy. There's no way around that, whether they're human-looking Star Trek creatures with antenna on their foreheads, or they're nothing more than single-cell organisms with collective mega-intelligence. And that entropy will almost certainly have strong feedback effects on their planet's habitability, as we are already beginning to see here on Earth."

Careful What You Look For

But we might not like what we find. It's possible, for example, that everyone runs into an environmental bottleneck. Energy extraction, and the resultant effects on the environment, could be the Great Filter that accounts for the Fermi Paradox. What's more, we may find that most exoplanets have extremely sensitive tipping points.

Plot of human population, total energy consumption and atmospheric CO2 concentration from 10,000 BCE to today as trajectory in SWEIT solution space. Note the coupled increase in all three quantities over the last century. Credit: Michael Osadciw/University of Rochester.

"If that's true, the question becomes whether we can learn anything by modeling the range of evolutionary pathways," notes Frank. "Some paths will lead to collapse and others will lead to sustainability. Can we, perhaps, gain some insight into which decisions lead to which kind of path?"

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The use of network theory — with its emphasis on multiple cascading paths to system failures or system resiliency — could therefore yield important insights. By studying past extinction events, by using tools to model the future evolutionary trajectory of our own species, and by positing the fate of still unknown alien civilizations, we might be able to inform decisions that might lead to a sustainable future.

Read the entire study at Anthropocene: "Sustainability and the astrobiological perspective: Framing human futures in a planetary context". Additional information via University of Rochester.

Top image via rich35211, JJasso and NEOGAF.

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