The Earth's average global temperatures have risen steadily since the Industrial Revolution. According to the National Oceanic and Atmospheric Agency (NOAA), the Earth has been warming 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 faster. What’s more, this trend is projected to increase by 1.5 to 2 °C (2.7 to 3.6 °F) by mid-century – possibly more! This is a direct consequence of the burning of fossil fuels, which has increased exponentially since the mid-19th century.
Depending on the magnitude of the temperature increase, the impact on Earth's habitability could be catastrophic. recent studyA team of scientists has examined how rising temperatures are a long-term problem facing advanced civilizations and not just a matter of fossil fuel consumption. Rising planetary temperatures, they argue, could be an inevitable result of exponential growth in energy consumption. Their findings could have serious implications for astrobiology and the environment. Search for extraterrestrial intelligence (Computer Systems Research Team).
The study was conducted by Amadeo Balbiassociate professor of astronomy and astrophysics at the University of Rome Tor Vergataand Manasvi LingamAssistant Professor of the Department of Aerospace, Physics and Space Sciences and the Department of Chemistry and Chemical Engineering to the Florida Institute of Technology (Florida Tech). The article detailing their findings, “Waste heat and habitability: limitations arising from technological energy consumption”, recently appeared online and is being reviewed for publication in the journal Astrobiology.
The idea that civilizations will eventually overheat their planet dates back to the work of Soviet scientist Mikhail I. Budyko, who in 1969 published a pioneering study entitled “The effect of variations in solar radiation on the Earth's climate”, where he argued that “All the energy used by man is transformed into heat, the greater part of this energy being an additional source of heat compared with the present gain in radiation. Simple calculations show that with the present rate of growth in energy use, 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 Lingam told Universe Today via email:
“The current contribution of waste heat to global temperature rise is minimal. However, if waste heat production continues on an exponential trajectory over the next century, another degree Celsius (1.8 F) of temperature increase may be due to waste heat, independent of an enhanced greenhouse effect due to fossil fuels. If waste heat generation continues its exponential growth for centuries, we show that it may eventually lead to a complete loss of habitability and the disappearance of all life on Earth.”
The Dyson sphere is a fitting example of the waste heat resulting from the exponential growth of an advanced civilization. In his original proposal, “Search for Artificial Stellar Sources of Infrared Radiation,” Freeman Dyson argued that the need for more habitable space and energy could eventually drive a civilization to create an “artificial biosphere completely surrounding its parent star.” As he described, these megastructures would be detectable by infrared instruments because of the “large-scale conversion of starlight into far-infrared radiation,” meaning they would radiate waste heat into space.
“The warming we analyse in our paper is the result of the conversion of any form of energy and is an inevitable consequence of the laws of thermodynamics,” added Balbi, lead author of the study. “For the present-day Earth, this warming represents only a negligible fraction of the warming caused by the anthropogenic greenhouse effect. However, if global energy consumption continues to grow at the current rate, this effect could become significant within a few centuries, potentially affecting the habitability of the Earth.”
To determine how long it would take advanced civilizations to reach the point where their home planet would become uninhabitable, Balbi and Lingam came up with theoretical models based on the Second Law of Thermodynamics (as applied to energy production). They then applied this to planetary habitability by considering the circumsolar habitable zone (CHZ) – that is, the orbits where a planet would receive enough solar radiation to sustain liquid water on its surface.
“We adapted the habitable zone calculation, a standard tool in exoplanetary studies. Basically, we incorporated an additional source of heat, derived from technological activity, along with stellar irradiation,” Balbi said. Another key factor they considered is the exponential growth rates of civilizations and their energy consumption, as predicted by the Kardashev scaleUsing humanity as a model, we see that world energy consumption rates It rose 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 over the same period (1 billion in 1800 to 8 billion in 2023). Balbi and Lingam extrapolated this trend to measure the implications for habitability and to determine the maximum lifespan of an advanced civilization once it has entered a period of exponential growth. They ultimately concluded that the maximum lifespan of technospheres is about 1000 years, provided they experience an annual growth rate of about 1% over the entire period of interest.
These findings, Balbi said, have implications for humanity and the Search for Extraterrestrial Intelligence (SETI):
“Our results indicate that the effect of residual heat could be substantial not only on the future of Earth, but also on the development of any hypothetical technological species inhabiting planets around other stars. Consequently, taking this constraint into account could influence how we approach the search for technologically advanced life in the universe and how we interpret the results of such searches. For example, it could offer a partial explanation of the Fermi paradox.”
Balbi and Lingam also highlight that these results present some possible recommendations for how we might prevent our planet from becoming uninhabitable. Again, there are implications for SETI, as any solution we can imagine is likely to have already been implemented by another advanced species. Balbi said:
“Although our paper focuses on physics rather than solutions to societal challenges, we imagine some scenarios that could help a technological species mitigate the limitations of debris warming and delay its onset. A sufficiently advanced civilization could use technology to counteract the warming, for example by employing stellar shielding.”
“Alternatively, they could move much of their technological infrastructure off-planet, into space. These engineering megaprojects 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 most plausible.”
Further reading: arXiv
