Universe Today
In the 1950s, famed physicist
Enrico Fermi
posed the question that encapsulated one of the toughest questions in the Search for Extra-Terrestrial Intelligence (SETI): "Where the heck is everybody?" What he meant was, given the age of the Universe (13.8 billion years), the sheer number of galaxies (between 1 and 2 trillion), and the overall number of planets, why has humanity still not found evidence of extra-terrestrial intelligence?
This question, which has come to be known as the "Fermi Paradox", is something scientists continue to ponder. In a
new study
, a team from the University of Rochester considered that perhaps Climate Change is the reason. Using a mathematical model based on the Anthropocene, they considered how civilizations and planet systems co-evolve and whether or not intelligent species are capable of living sustainability with their environment.
The study, titled "
The Anthropocene Generalized: Evolution of Exo-Civilizations and Their Planetary Feedback
", recently appeared in the scientific journal
Astrobiology.
The study was led by Adam Frank, a professor of physics and astronomy at the University of Rochester, with the assistance of Jonathan Carroll-Nellenback (a senior computational scientist at Rochester) Marina Alberti of the University of Washington, and Axel Kleidon of the
Max Planck Institute for Biogeochemistry
.
Today, Climate Change is one of the most pressing issues facing humanity. Thanks to changes that have taken place in the past few centuries - i.e. the industrial revolution, population growth, the growth of urban centers and reliance on fossil fuels - humans have had a significant impact on the planet. In fact, many geologists refer to the current era as the "Anthropocene" because humanity has become the single greatest factor affecting planetary evolution.
In the future, populations are expected to grow even further, reaching about
10 billion
by mid-century and over
11 billion
by 2100. In that time, the number of people who live within urban centers will also increase dramatically, increasing from
54% to 66% by mid-century
. As such, the quesiton of how billions of people can live sustainably has become an increasingly important one.
Prof. Frank, who is also the author of the new book
*Light of the Stars: Alien Worlds and the Fate of the Earth*
(which draws on this study), conducted this study with his colleagues in order to address the issue Climate Change in an astrobiological context. As he explained in a University of Rochester
press release
:
Using the Anthropocene as an example, one can see how civilization-planet systems co-evolve, and how a civilization can endanger itself through growth and expansion - in what is known as a "
progress trap
". Basically, as civilizations grow, they consume more of the planet's resources, which causes changes in the planet's conditions. In this sense, the fate of a civilization comes down to how they use their planet's resources.
In order to illustrate this process Frank and his collaborators developed a mathematical model that considers civilizations and planets as a whole. As Prof. Frank
explained
:
The model was also based on case studies of extinct civilizations, which included the famous example of what became of the inhabitants of Rapa Nui (aka. Easter Island). According to archaeological studies, the people of the South Pacific began colonizing this island between 400 and 700 CE and its population peaked at 10,000 sometime between 1200 and 1500 CE.
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Professor Adam Frank, who led the study in how civilization-planet systems evolve. Credit: University of Rochester photo / J. Adam Fenster
[/caption]
By the 18th century, however, the inhabitants had depleted their resources and the population declined to just 2000. This example raises the important concept known as "carrying capacity", which is the maximum number of species an environment can support. As Frank explained, Climate Change is essentially how the Earth responds to the expansion of our civilization:
Using their mathematical model, the team identified four potential scenarios that might occur on a planet. These include the Die-Off scenario, the Sustainability scenario, the Collapse Without Resource Change scenario, and the Collapse With Resource Change scenario. In the
Die-Off
scenario, the population and the planet's state (for example, average temperatures) rise very quickly.
This would eventually lead to a population peak and then a rapid decline as changing planetary conditions make it harder for the majority of the population to survive. Eventually, a steady population level would be achieved, but it would only be a fraction of what the peak population was. This scenario occurs when civilizations are unwilling or unable to change from high-impact resources (i.e. oil, coal, clear-cutting) to sustainable ones (renewable energy).
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Four scenarios for the fate of civilizations and their planets, based on mathematical models developed by Adam Frank and his collaborators. Credit: University of Rochester illustration / Michael Osadciw
[/caption]
In the
Sustainability
scenario, the population and planetary conditions both rise, but eventually come to together with steady values, thus avoiding any catastrophic effects. This scenario occurs when civilizations recognize that environmental changes threaten their existence and successfully make the transition from high-impact resources to sustainable ones.
The final two scenarios -
Collapse Without Resource Change
and
Collapse With Resource Change
- differ in one key respect. In the former, the population and temperature both rise rapidly until the population reaches a peak and begins to drop rapidly - though it is not clear if the species itself survives. In the latter, the population and temperature rise rapidly, but the populations recognizes the danger and makes the transition. Unfortunately, the change comes too late and the population collapses anyway.
At present, scientists cannot say with any confidence which of these fates will be the one humanity faces. Perhaps we will make the transition before it is too late, perhaps not. But in the meantime, Frank and his colleagues hope to use more detailed models to predict how planets will respond to civilizations and the different ways they consume energy and resources in order to grow.
From this, scientists may be able to refine their predictions of what awaits us in this century and the next. It is during this time that crucial changes will be taking place, which include the aforementioned population growth, and the steady rise in temperatures. For instance, based on
two scenarios
that measured CO2 increases by the year 2100, NASA indicated that global temperatures could rise by either 2.5 °C (4.5 °F) or 4.4 °C (8 °F).
In the former scenario, where CO2 levels reached 550 ppm by 2100, the changes would be sustainable. But in the latter scenario, where CO2 levels reached 800 ppm, the changes would cause widespread disruption to systems that billions of humans depends upon for their livelihood and survival. Worse than that, life would become untenable in certain areas of the world, leading to massive displacement and humanitarian crises.
In addition to offering a possible resolution for the Fermi Paradox, this study offers some helpful advice for human beings. By thinking of civilizations and planets as a whole - be they Earth or exoplanets - researchers will be able to better predict what changes will be necessary for human civilization to survive. As Frank
warned
, it is absolutely essential that humanity mobilize now to ensure that the worst-case scenario does not occur here on Earth:
And be sure to enjoy this video that addresses Prof. Frank and his team's research, courtesy of the University of Rochester:
Further Reading: University of Rochester
,