Humanity’s impact on the climate is clear and devastating. Over the last two hundred years or so, we have pumped enough greenhouse gas into the atmosphere to significantly increase its temperature and raise the frightening prospect of much of the Earth becoming uninhabitable.
The current plan to avoid this fate is to reduce net carbon emissions to zero within the next 20 years. That will surely help, provided Earth has not moved beyond any significant tipping points by then.
But there is another problem looming that net zero will do little to mitigate. The so-called “deep warming” problem comes from the unavoidable fact that almost all energy humans use ultimately ends up in the environment as low-level heat. That’s all the energy from solar, wind, nuclear, geothermal, fossil fuels and other sources.
For the moment, the amount of heat humans generate in this way is tiny compared to the energy from the Sun. But if our energy consumption continues to grow at exponential rates, an important question is when this will eventually rival solar heating and how it will impact the habitability of the Earth.
Heat Death
Now Amedeo Balbi at the University of Rome in Italy and Manasvi Lingam at the Florida Institute of Technology have calculated the timescales over which deep heating will impact Earth and how it will depend on the mitigating strategies humans employ. Their calculations also have important implications for the search for intelligent life on other planets.
The fate of all energy used on Earth is ultimately determined by the second law of thermodynamics. This states that in any energy transfer, the total entropy, or disorder, of a closed system always increases over time. In other words, no energy conversion process is perfectly efficient, and some is always lost, typically in the form of heat.
If humanity’s energy usage continues to grow at about 1 percent per year, an exponential rate, the consequences will be inevitable, say the researchers. Their model suggests that waste heat will eventually raise global temperatures enough to impact the habitability of the planet.
“We demonstrate that the loss of habitable conditions on such terrestrial planets may be expected to occur on timescales of ≲ 1000 years,” they say. Humanity is already two hundred years into this process following the Industrial Revolution.
Balbi and Lingam point out that this heating effect would persist even if all energy sources were carbon-free. The problem is not emissions; it’s the heat itself.
It’s easy to imagine that waste heat from photovoltaic sources would not increase the temperature of the planet because sunlight hits the planet whether or not it is converted to electricity.
However, Balbi and Lingam point out that solar panels absorb light that would otherwise be reflected back into space. And so this process inevitably injects extra heat into the environment.
Unchecked Growth
Balbi and Lingam consider three ways this might play out. In the first, waste energy leads to runaway heating that effectively cooks the planet and drives humanity to extinction. The result is self-destruction through unchecked growth.
A second trajectory is to find ways to halt the exponential growth of energy use, by improving efficiency and reducing the amount of energy use. This approach would require a cultural shift towards prioritizing long-term sustainability over constant growth, a shift humanity does not seem well suited to make. But it might allow a civilization to thrive without overwhelming its environment.
The final scenario is to expand civilization into space. By spreading out, humans could manage waste heat more effectively and avoid turning Earth into an oven.
Other civilizations will face the same scenario and that will have important implications for our ability to find and contact them — the famous Fermi paradox. Balbi and Lingam suggest that if most technological species grow until they cook their own planets, they may never reach a stage where they’re around long enough for us to detect them.
The Italian physicist Enrico Fermi famously asked: if advanced civilizations are out there, why haven’t we seen them. “This outcome might offer a (partial) “solution” to the famous Fermi paradox,” they suggest.
However, Balbi and Lingam point out that even if advanced civilizations eventually boil themselves into extinction, we may still be able to see technosignatures that outlive them. These artifacts could include remnants of energy infrastructure, urban heat islands, or other traces of technological activity.
The priority today is clearly to reduce net carbon emissions to zero. But the message from Balbi and Lingam (and various others who have studied this problem) is that if we eventually tackle this problem, we will soon have another existential threat on our hands in the form of waste heat death.
Ref: Waste Heat and Habitability: Constraints from Technological Energy Consumption: arxiv.org/abs/2409.06737
