Inferring the Climates of Red Dwarf Planets

Planets orbiting red dwarf stars are unique compared to other star systems because such planets are prone to falling into synchronous rotation, so that one side experiences perpetual day and the opposite side resides in permanent night. Such planets could still be habitable, sustaining liquid water and perhaps even life, so such systems continue to be targeted in the search for signs of life on exoplanets.

One starting point to looking for life on such worlds is to infer properties of an exoplanet climate from astronomical data. Eric Wolf, Ravi Kopparapu, and myself examine this problem in a paper titled “Simulated phase-dependent spectra of terrestrial aquaplanets in M dwarf systems” and published in The Astrophysical Journal. Infrared emission and reflected stellar light from a planet changes as it orbits its host star. We should that observations of these orbital changes in thermal energy could provide important information on the circulation state of the planet, the location of major cloud decks, and the abundance of water vapor. As the next generation of space telescope are designed and launched, methods such as these will become important tools for understanding the potential of M-dwarf systems to support life.

Greenhouse Warming on Earth’s Past, Present, and Future

Carbon dioxide in Earth’s atmosphere provides an important regulator of climate. Without it, or with too little, Earth would be completely frozen. But the rapid rise in carbon dioxide in recent times due to fossil fuel consumption and changes in land use has caused unprecedented warming with consequences to human civilization.

Understanding how Earth’s climate responds to atmospheric carbon dioxide is an important problem not only for anthropogenic climate change today but also for understanding Earth’s distant past (when the sun was fainter than today) and distant future (when the sun becomes brighter than today). In a paper by Eric Wolf, Brian Toon, and myself titled “Evaluating climate Sensitivity to CO2 across Earth’s history” and published in Journal of Geophysical Research – Atmospheres, we calculate the expected warming for early-, modern-, and future-Earth scenarios across a much wider range of carbon dioxide levels than typically considered for present-day climate change. We show that a doubling of atmospheric carbon dioxide would have caused a greater amount of warming on early Earth (when the carbon dioxide fraction of the atmosphere was high) compared to today (when carbon dioxide is a trace constituent). In general the amount of warming to be expected from such a carbon dioxide doubling (known as the “climate sensitivity”) depends upon the amount of solar energy received, the starting carbon dioxide budget, and the mean temperature of the planet.

Paying for Space Settlement

Bold visions for the human settlement of Mars, and perhaps beyond, would require unprecedented technical management over successive generations. Space settlement can also only succeed with an uninterrupted and sufficient supply of resources, as the unique dangers of space would make food, water, and even breathable air scarce and expensive resources. Gradually building the infrastructure of a permanent space settlement would also be costly, and unlikely to provide any direct financial benefits to investors in a timely manner.

I recently published a chapter titled “Can deep altruism sustain space settlement?” in the book The Human Factor in a Mission to Mars. In this chapter I explore the idea of “deep altruism,” where a donor is concerned not with benefits to themselves or kin but to distant future descendants for whom they may have no direct connection. Similar to a time capsule or other grand construction or big science projects in human history, space settlement may provide benefits to the distant future that are not easily identifiable today. Wealthy individuals, foundations, and corporations interested in the permanent human settlement of space may find the idea of investing in humanity’s long-term future to be valuable and worthwhile, even if the return on investment is not immediately obvious.

Commercial interests will likely be an important factor as space industries expand. But investment in space infrastructure out of deep altruism can complement market forces in establishing a sustainable human presence in space.

Detectability of Future Earth

This special issue of the journal Futures features papers that examine the future of Earth and civilization from an astrobiological perspective, particularly focused on the extent to which human activities could be detectable across interstellar distances. As the guest editor of this special issue, my paper “Introduction: Detectability of future Earth” provides a synthesis of all the contributions in the volume.

This collection of papers demonstrates an important connection between futures studies and the search for extraterrestrial intelligence. The first issue is to examine possible future trajectories for human civilization: our growth in population and energy consumption will eventually face limits, even with advances in technology. This hybridization of the planet with technology is uncharted territory in Earth’s history, with an uncertain future or trajectory. The second issue is whether or not any other civilizations in the galaxy have already passed through this trajectory by achieving a sustainable hybridization of technology with their own planet. Evidence of such civilizations would be good news for humanity, as this would mean that our own future includes viable options for longevity. But if the search for extraterrestrial life turns up nothing, then this may indicate that energy-intensive civilizations might not be sustainable at all on a galactic scale. Our challenge as a species is to critically examine our possible futures and identify strategies for increasing the longevity of our civilization.

The collection of papers from this special issue on the Detectability of Future Earth is available on the Futures website.


Jacob Haqq-Misra (2019) Introduction: Detectability of future Earth, Futures 106: 1-3.
This special issue emphasizes the connection between the unfolding future of the Anthropocene with the search for extraterrestrial civilizations.

Brendan Mullan & Jacob Haqq-Misra (2019) Population growth, energy use, and the implications for the search for extraterrestrial intelligence, Futures 106: 4-17.
Limits to growth in population and energy consumption could occur within 2-3 centuries, which might imply that energy-intensive extraterrestrial civilizations are also rare.

Gina Riggio (2019) Earth in Human Hands, by David Grinspoon., Futures 106: 18-19.
This book review highlights Grinspoon’s observation that we are entering a new epoch of planetary self-awareness.

Julia DeMarines (2019) Light of the Stars: Alien Worlds and the Fate of the Earth, by Adam Frank., Futures 106: 20.
This book review highlights the connections between the future of Earth and the possibility of extraterrestrial civilizations.

Carl L. DeVito (2019) On the Meaning of Fermi’s paradox, Futures 106: 21-23.
This mathematical treatment of the Fermi paradox suggests that civilizations in the galaxy may emerge very slowly.

S. Stoney Simons & Jacob Haqq-Misra (2019) A trip to the moon might constrain the Fermi Paradox, Futures 106: 24-32.
Building a lunar observatory at mid-infrared wavelengths could help to improve the search for biosignatures.

Jacob Haqq-Misra (2019) Policy options for the radio detectability of Earth, Futures 106: 33-36.
Earth’s future radio detectability depends upon the risks we assume about the possibility of extraterrestrial contact.

Sanjoy M. Som (2019) Common identity as a step to civilization longevity, Futures 106: 37-43.
Civilization can extend it’s longevity through early-childhood psychology education based upon the “overview effect” of observing Earth from space.