Earth’s average global temperatures have been steadily increasing since the Industrial Revolution. According to the National Oceanic and Atmospheric Agency (NOAA), Earth has been heating up at a rate of 0.06 °C (0.11 °F) per decade since 1850 – or about 1.11 °C (2 °F) in total. Since 1982, the average annual increase has been 0.20 °C (0.36 °F) per decade, more than three times as fast. What’s more, this trend is projected to increase by between 1.5 and 2 °C (2.7 to 3.6 °F) by mid-century, possibly more! This is a direct consequence of burning fossil fuels, which has increased exponentially since the mid-19th century.

Depending on the extent of temperature increases, the impact on Earth’s habitability could be catastrophic. In a recent study, a team of scientists examined how temperature increases are a long-term issue facing advanced civilizations and not just a matter of fossil fuel consumption. As they argue, rising planetary temperatures could be an inevitable result of the exponential growth of energy consumption. Their findings could have serious implications for astrobiology and the Search for Extraterrestrial Intelligence (SETI).

The study was conducted by Amedeo Balbi, an Associate Professor of Astronomy and Astrophysics at the Universita di Roma Tor Vergata, and Manasvi Lingam, an Assistant Professor with the Department of Aerospace, Physics and Space Sciences and the Department of Chemistry and Chemical Engineering at the Florida Institute of Technology (FIT). The paper detailing their findings, “Waste Heat and Habitability: Constraints from Technological Energy Consumption,” recently appeared online and is being considered for publication in the journal Astrobiology.

The idea that civilizations will eventually overheat their planet harkens back to the work of Soviet scientist Mikhail I. Budyko. In 1969, he published a groundbreaking study titled “The effect of solar radiation variations on the climate of the Earth,” where he argued that “All the energy used by man is transformed into heat, the main portion of this energy being an additional source of heat as compared to the present radiation gain. Simple calculations show that with the present rate of growth of using energy the heat produced by man in less than two hundred years will be comparable with the energy coming from the Sun.”

This is a simple consequence of all energy production and consumption invariably producing waste heat. While this waste heat is only a marginal contribution to global warming compared to carbon emissions, long-term projections indicate that this could change. As Lingham related to Universe Today via email:

“The current contribution of waste heat to a rise in global temperature is minimal. However, if waste heat production proceeds on an exponential trajectory for the next century, a further 1 degree Celsius (1.8 F) rise in temperature may stem from waste heat, independent of an enhanced greenhouse effect because of fossil fuels. If the waste heat generation maintains its exponential growth over centuries, we show that it can eventually lead to a complete loss of habitability and the demise of all life on Earth.”

The Dyson Sphere is a fitting example of waste heat resulting from the exponential growth of an advanced civilization. In his original proposal paper, “Search for Artificial Stellar Sources of Infrared Radiation,” Freeman Dyson argued how the need for more habitable space and energy could eventually drive a civilization to create an “artificial biosphere which completely surrounds its parent star.” As he described, these megastructures would be detectable to infrared instruments due to the “large-scale conversion of starlight into far-infrared radiation,” meaning they would radiate waste heat to space.

“The heating we explore in our paper results from the conversion of any form of energy and is an unavoidable consequence of the laws of thermodynamics,” added Balbi, who was the study’s lead author. “For present-day Earth, this heating represents only a negligible fraction of the warming caused by the anthropogenic greenhouse effect. However, if global energy consumption continues to grow at its current rate, this effect could become significant within a few centuries, potentially impacting Earth’s habitability.”

To determine how long it would take for advanced civilizations to reach the point where they would render their home planet uninhabitable, Balbi and Lingam crafted theoretical models based on the Second Law of thermodynamics (as it applies to energy production). They then applied this to planetary habitability by considering the circumsolar habitable zone (CHZ) – i.e., the orbits where a planet would receive sufficient solar radiation to maintain liquid water on its surface.

“We adapted the calculation of the habitable zone, a standard tool in exoplanetary studies. Essentially, we incorporated an additional source of heating—stemming from technological activity—alongside the stellar irradiation,” said Balbi. Another key factor they considered is the exponential growth rates of civilizations and their energy consumption, as predicted by the Kardashev Scale. Using humanity as a template, we see that global energy consumption rates went from 5,653 terawatt-hours (TWh) to 183,230 TWh between 1800 and 2023.

This trend was not only exponential but accelerated over time, similar to population growth in the same period (1 billion in 1800 to 8 billion in 2023). Balbi and Manasavi extrapolated this trend to measure the implications for habitability and determine the maximum lifespan of an advanced civilization once it has entered a period of exponential growth. Ultimately, they concluded that the maximum lifetime of technospheres is about 1000 years, provided that they experience an annual growth rate of about 1% throughout the period of interest.

These findings, said Balbi, have implications for humanity and in the Search for Extraterrestrial Intelligence (SETI):

“Our results indicate that the effect of waste heat could become substantial not only in Earth’s future but also in the development of any hypothetical technological species inhabiting planets around other stars. Consequently, considering this constraint could influence how we approach the search for technologically advanced life in the universe and how we interpret the outcomes of such searches. For instance, it may offer a partial explanation for the Fermi paradox.”

Balbi and Lingam also stress how these results present some possible recommendations for how we could avoid rendering our planet uninhabitable. Once again, there are implications for SETI since any solution we can envision is likely to have already been implemented by another advanced species. Said Balbi:

“Although our paper focuses on physics rather than solutions to societal challenges, we envision a few scenarios that could help a technological species mitigate the constraints of waste heating and delay its onset. A sufficiently advanced civilization might use technology to counteract heating, such as employing stellar shielding.”

“Alternatively, they could relocate much of their technological infrastructure off-world, moving into space. Such mega-engineering projects would have significant implications for our search for technosignatures. A less ambitious but perhaps more feasible approach would be to reduce energy consumption by slowing growth. Of course, we cannot predict which of these options is the most plausible.”

Further Reading: arXiv