Where can air conditioning get an apology? In June, Paris Deputy Mayor Audrey Pulvar blamed American energy use for Europe’s deadly heat wave. “As the second-largest emitter of greenhouse gas emissions in the world, you bear a significant amount of responsibility for global warming and the consequences we, in France, are experiencing,” Pulvar postured. “Your cities’ ‘90% air-conditioned’ are not unrelated to this. In Paris, we take responsibility.”

Days later, however, a paper by British and Spanish researchers suggested that the “responsibility” of enduring summer without modern conveniences might just be so much needless suffering.

The paper, published June 30 in Geophysical Research Letters, found that “the increase of European summer temperatures … is largely associated … with a decrease of sulfate aerosol emissions over Europe starting from 1980.”

Sulfate particles are a common form of air pollution, causing air quality issues, respiratory problems, and acid rain. They are most commonly emitted by burning fossil fuels, but only as a byproduct. Burning hydrocarbons releases carbon dioxide and water vapor into the atmosphere. Sulfates are only emitted when sulfur-based impurities in the fuel (usually coal) are burned along with the hydrocarbons.

Thus, advanced economies have responded to sulfate pollution by seeking “cleaner” fuel sources. Originally, this meant either finding coal, oil, and gas deposits with less naturally-occurring sulfur, or (less commonly) scrubbing out the sulfur before the fuel was burned. In 1987, Europe adopted the Montreal Protocol, which significantly reduced the levels of sulfate pollution in the atmosphere.

However, sulfates had a secondary effect which is relevant to this new paper. Sulfates acted as a solar shield of sorts, reflecting the sun’s radiation back into space — the opposite of a greenhouse gas effect. When Europe purged its air of sulfate pollution, it also made its air warmer.

The researchers connected Europe’s heat waves with a second atmospheric phenomenon, also related to cleaner air. Apparently, reducing sulfate pollution not only made Europe warmer, but it also made the poles warmer. This lowered the temperature differential between the poles and the equator, which resulted in a more stable jet stream. A more stable jet stream means more stable bodies of air. For Europe, this meant that the new heat waves they experienced would stick around much longer.

The paper made both causal and temporal connections between the removal of sulfate pollution and warmer European summers. “The contribution of aerosols has a turning point around 1980, coinciding with a reduction of sulfate aerosol emissions over Europe resulting from the Montreal Protocol,” the authors wrote. While sulfate emissions increased over Europe from 1940 to 1980, temperatures declined. After Europe acted to minimize sulfate emissions in the 1980s, temperatures increased.

The researchers stumbled across this conclusion because of errors in existing climate models. Essentially, current climate models predict global warming, but they “underestimate the magnitude of these changes, showing signal-to-noise errors in the atmospheric circulation responses” observed across Western and Central Europe. So, the authors went looking for another explanatory factor. When corrected for the effect of eliminated sulfate emissions, they said, the models could correctly predict observed warming trends in Europe.

This finding suggests a lesson in humility for scientists and policymakers. An international effort to correct a pollution problem may have played a role in creating a warming problem. This does not mean that anti-pollution protocols are bad. It does mean they led to unanticipated negative side-effects (or, at least, an unanticipated magnitude of the side-effects). With all the advances in modern science, there is still much about the world humanity’s best minds do not know.

Forty years later, this principle remains relevant to policy disputes. Whether it is climate change policy, COVID policy, or WHO protocols for the next pandemic, powerful decisionmakers often try to make long-term policy based on one moment’s snapshot of scientific opinion, without much regard for the ways that policy may be harmful to freedom, human dignity, economic growth, or other timeless values. The truth is, science is continually developing; new studies are published, new results are found, and old givens are continually challenged.

This does not mean that we should reject all conclusions of modern science. It does mean that we should approach science with caution and a dash of skepticism. Where the word of God is silent, we cannot do better than act according to the best lights of reason today. But we must always keep one question in mind: if what we know today turns out to be wrong tomorrow, how much would we regret the decisions that we make? Prudence would counsel us to make decisions that leave us with the least regret.