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.

Limits to Growth

Human population continues to grow, with recent United Nation projections estimating over 11 billion people by 2100. Likewise, global energy use continues to grow at an exponential rate as we all seek higher standards of living. Technology continues to increase resources and reduce costs for everyone, but can this growth in population and technology continue indefinitely?

One of the first scientists to examine this question was Sebastian von Hoerner, a radio astronomer who conducted most of his research at the Green Bank Observatory in West Virginia. Von Hoerner argued in 1975 that continued growth of energy consumption on Earth would eventually start to contribute direct heating to the planet. (This is a consequence of the conservation of energy and is a separate issue from the emission of fossil fuels.) Even if technology is able to continually lower costs, we will eventually reach a limit to growth where our technology itself starts to warm the planet.

In a paper titled “Population growth, energy use, and the implications for the search for extraterrestrial intelligence,” part of the Futures special issue on the Detectability of Future Earth, Brendan Mullan and I update von Hoerner’s approach to calculate limits to population and energy growth. We demonstrate that Earth could conceivably support up to 20 billion people by optimizing current farmland or up to 100 billion people if all available land were dedicated to agriculture. These limits would require everyone to adopt a strict vegetarian diet and a life of poverty, so increasing the average standard of living would decrease the total carrying capacity. We also show that direct thermal heating of the planet from increased energy use could occur in the 2300’s to 2400’s if energy growth continues at a rate of about 2% per year.

If our civilization ever reaches this point, then our energy consumption as a civilization will equal the total energy Earth receives from the Sun. If such an endpoint is possible and sustainable, then any advanced extraterrestrial civilizations may already have achieved such an energy-intensive state. If we do eventually discover that energy-intensive civilizations are commonplace enough in the galaxy, then we can have greater confidence that our own future will survive any transitions as we approach limits to growth. But if energy-intensive civilizations are rare, or if we are the only ones, then our challenge for the future is even greater. The long-term success of civilization on Earth depends upon how we manage our population and energy growth over subsequent generations.

The Risk of Transmitting to Space

The idea of messaging to extraterrestrial intelligence (METI) suggests that a possible way to establish contact with civilizations on other planets is to first send transmissions ourselves. The search for extraterrestrial intelligence (SETI) has traditionally followed a passive listen-only mode to detect any alien transmissions headed our way. If everyone is listening and nobody is transmitting, then METI might be the way to attract attention.

But is attracting attention from extraterrestrial civilizations necessarily good? We have no idea if contact with extraterrestrial beings would benefit or harm humanity, or even be completely neutral in its impact. Some scientists are unconcerned about possible risks and suggest that METI transmissions should occur whenever they are viable. Others worry that METI transmissions could expose Earth to significant risk and argue in favor of a moratorium on METI activities.

I recently published a paper titled “Policy options for the radio detectability of Earth” in the Futures special issue on the Detectability of Future Earth. In this paper, I argue that the METI risk problem cannot be conclusively decided until contact with extraterrestrial intelligence actually occurs. This implies that any moratorium on METI activities cannot be based on the requirement for new information, as the only new information that would actually suffice is the actual discovery of alien life. Following from this conclusion, there are three possible policy options for proceeding with SETI and METI:

  1. Precautionary malevolence – alien contact is likely to be harmful, so we should not engage in METI until SETI succeeds.
  2. Assumed benevolence – alien contact is likely to be helpful, so we should engage in METI along with SETI.
  3. Preliminary neutrality – alien contact is unlikely to occur at all, so we may as well do SETI and METI if funds are available.

All three of these policies remain viable options until we actually discover extraterrestrial intelligence and learn the actual risks to humanity. Precautionary malevolence would imply that human civilization should reduce all of its transmission activities so as to minimize its detectability by alien observers. Likewise, assumed benevolence implies that greater transmissions from Earth would increase the chances of contact. But both of these policies are optimistic about the likelihood of contact with alien life. Perhaps a more pragmatic approach is preliminary neutrality, which would remain consistent with business-as-usual on Earth and would not recommend any significant changes to Earth’s future detectability.

A Lunar Telescope Might Help Us Find Aliens

One way to search for extraterrestrial life is to look for tell-tale signs of biology in the atmospheres of planets orbiting other star systems. Such a “biosignature” that shows the simultaneous presence of oxygen, water vapor, and methane, for example, would be consistent with the presence of surface life on a planet. Observing biosignatures on other planets is a difficult feat, but current and future ground- and space-based telescopes are gradually enabling these observations.

Another place to build a telescope for observing biosignatures is the moon. Stoney Simons and I explore this idea in a recent paper titled “A trip to the moon might constrain the Fermi Paradox,” which is part of the Futures special issue on the Detectability of Future Earth. The moon’s negligible atmosphere makes observations much easier than ground-based astronomy, particularly at the mid-infrared wavelengths needed to detect possible biosignatures.

Searching for biosignatures in the infrared provides a quantitative method of constraining the abundance of life in the galaxy. Likewise, the possibility of observing “technosignatures” in the atmospheres of distant planets could betray the presence of extraterrestrial intelligence. Actually finding any definitive biosignatures or technosignatures will require at least a couple more decades of observing, but we suggest that a lunar observatory should remain an option for contributing to this search.