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.

Is Climate Change Ever Good?

The cumulative effects of human actions over past centuries such as widespread deforestation and the abundant use of fossil fuels has caused changes in the present climate state that would otherwise not have occurred. This trend of an increase in the global average temperature shows no evidence of slowing into the future, which suggests that uncomfortable climate change will persist in the centuries to come. Most of the problematic aspects of climate change involve its negative impact on humans. This includes shifts in farmable regions of the world, destabilization of parts of the world due to fluctuating food prices, changes in flooding and drought patterns, and forced migration due to sea level rise.

A warming planet might pose problems for humans, but how would climate change affect the welfare of other species on Earth? In a recent paper titled “Is climate change morally good from non-anthropocentric perspectives?” and published in Ethics, Policy and Environment, Toby Svoboda and I examine the impact of climate change on non-human organisms. If we temporarily set aside the interests of humans, might it be possible that climate change provides net benefits to other organisms?

The context of this study is the belief by some people in “nonanthropocentrism” or “anti-humanism” as a philosophy. Such beliefs tend to place human interests beneath those of other organisms in Earth’s community of life. If such philosophical positions are accepted at face value, then this might suggest that climate change is in fact a good thing. Climate change might cause the decline of civilization and even a reduction in biodiversity, but it might allow other organisms to flourish as a result. The net effect could be a much more thriving planet, albeit one in which humans are worse off.

This is not to say that we should ignore the effects of climate change on humans. Instead, this analysis demonstrates that nonanthropocentrism and anti-humanism may be in conflict with modern attempts at mitigating climate change. Our analysis therefore challenges adherents of nonanthropocentric ethics to examine the extent to which non-human interests should take priority over the collective interests of human civilization.