In a paper published this week in the journal Nature Climate Change, scientists conclude that heat from energy use in large urban areas can collectively alter the character of the jet stream and other major atmospheric systems.
According to the study (“Energy consumption and the unexplained winter warming over northern Asia and North America”), this heat energy can lead to surface temperature changes as large as 1 degree C (1.8 degrees F) thousands of miles from urban heat sources. Moreover, the authors claim this thermal pollution can account for the “unexplained” winter warming over northern latitudes of Eurasia and North America continents.
(Note: “unexplained” here means the difference between observed climate changes not accounted for by current state-of-the-art climate models.)
That’s quite a claim. But how seriously should it be taken? In my opinion, it’s much to do about not much, although the nature of this new possible contributor to climate change is interesting.
To begin, what do we mean by thermal pollution, sometimes also called “waste heat”?
Whenever we humans generate energy, such as through burning of fossil fuels to generate electricity at power plants, power automobiles, heat buildings, etc., etc., much of it is immediately dissipated as “waste heat” into the environment. The remaining “usable” energy eventually dissipates as heat.
For example, in conventional automobile engines it’s known that 70 percent of the energy produced from gasoline is dissipated directly to the atmosphere through the radiator and exhaust pipe. Only 30 percent of the energy is used to actually move the car, but even that is dissipated as heat through braking and road friction.
The same principle applies to any and all activities that convert fuel to energy (including nuclear power) and, thereby, contributes to thermal pollution.
The study analyzes whether the magnitude and distribution of thermal pollution is sufficient to be a meaningful contributor to global and regional climate change.
(Note: thermal pollution is distinct from the urban heat island effect where solar radiation is absorbed by man-made structures in large urban areas and re-radiated or transferred via conduction to the environment.)
The authors find that, in total, the magnitude of the thermal pollution around the globe is very small (nearly negligible) in comparison to estimates of the influence of the “greenhouse effect” from rising levels of atmospheric carbon dioxide (CO2).
But they, nevertheless, hypothesize that the heating can influence climate over large regions even well-removed from the source of the heat.
To test this hypothesis, they quantify the effects of the thermal pollution on regional climate (not surprisingly) using a climate model to evaluate the differences between simulations with and without representation of the heat energy. They find the model simulations that include the heat energy best match the observed climate change.
But this approach almost always (if not always, at this time) encounters the Achilles Heal of insufficient model resolution to be trustworthy at the regional level (e.g., over the Mid-Atlantic states). This is especially true with the specific model employed in this study.
Moreover, the experiment only uses this single model. No single model alone can ever be considered sufficient to estimate the effects and uncertainties of any potential contributor to climate change.
To be sure, the results demonstrate a sensitivity in the regional climate to thermal pollution (see figures) as described. However, their significance in the real world is unsupported in the context of the reservations just mentioned.
Furthermore, the authors do not provide an adequate explanation of the physical mechanisms attributable to the effects of the thermal pollution. The discussion of the systematic effects on the jet stream and ties to the supposed higher frequency of troughs (low pressure) and ridges (high pressure) along coastlines is far from convincing.
My reservations about the methodology employed notwithstanding, some influence of thermal pollution on regional climate is plausible. And one cannot disagree with the authors that further study is warranted.