Triggering A Climate Change Dominated "Anthropocene": Is It Common Among Exocivilizations?

Shown above is a scatter plot of gamma versus the time for civilizations to decline by 20% of the their peak population. The solid black line shows our analytically derived collapse time, given by equation (15). The colors represent different values of our population-temperature tolerance parameter ∆T. The black dotted lines divide the graph into three regions. The leftmost region corresponds to low γ and high θ. This region results largely in overpopulation, which is the reason behind the long decline times. The middle region corresponds to both high γ and high θ, where technology is able to accelerate birth rates, but eventually ends up contributing to an increased death rate and short decline time. The rightmost region corresponds to a high γ and a low θ, where climate changes on a faster timescale then both technology and population growth. Thus, in this region, civilizations experience climate change before they experience any growth benefits due to technology. This means that these civilizations reach only a tiny fraction of their carrying capacity before they begin to decline.

We seek to model the coupled evolution of a planet and a civilization through the era when energy harvesting by the civilization drives the planet into new and adverse climate states.

In this way we ask if triggering "anthropocenes" of the kind humanity is experiencing now might be a generic feature of planet-civilization evolution. In this study we focus on the effects of energy harvesting via combustion and vary the planet's initial atmospheric chemistry and orbital radius. In our model, energy harvesting increases the civilization's population growth rate while also, eventually, leading to a degradation of the planetary climate state (relative to the civilization's habitability.)

We also assume the existence of a Complex Life Habitable Zone in which very high levels of CO2 are detrimental to multi-cellular animal life such as those creating technological civilizations. Our models show that the civilization's growth is truncated by planetary feedback (a "climate dominated anthropocene") for a significant region of the initial parameter space.

Ethan Savitch, Adam Frank, Jonathan Carroll-Nellenback, Jacob Haqq-Misra, Axel Kleidon, Marina Alberti

Comments: 19 pages, 13 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Popular Physics (physics.pop-ph)
Cite as: arXiv:2103.06330 [astro-ph.EP] (or arXiv:2103.06330v1 [astro-ph.EP] for this version)
Submission history
From: Ethan Savitch
[v1] Wed, 10 Mar 2021 20:25:28 UTC (9,125 KB)
Astrobiology, SETI,

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