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Sep 25, 2023

Recently, some big climate news happened: A paper published in a premier environmental journal, Nature Communications, asserted that a collapse of the Atlantic meridional overturning circulation (AMOC) could happen as early as 2025 and is likely to occur between 2025 and 2095. Such a collapse would be a huge deal—but keep in mind the Intergovernmental Panel on Climate Change has been saying exactly the opposite and that a collapse is unlikely. When “the science” doesn’t agree, how are policy experts supposed to educate policymakers?

Many people have likely never heard of the AMOC, but it is an underwater current in the Atlantic Ocean that brings warm water northward from the equator. It is because of the AMOC that the French Riviera can be the same latitude as Toronto, yet have a far warmer climate. It collapsed once about 14,500 years ago, and a collapse today would cause Northern European temperatures to fall by 14 degrees Fahrenheit. In addition to a colder Europe, a collapse would mean the equatorial regions would get warmer and wind currents would shift, which could cause food-producing regions in Africa to receive less rainfall. When it comes to the worst potential impacts of climate change, an AMOC collapse is one of the most serious.

Prior studies relied on direct observation of the AMOC, which we’ve only been observing since 2004. This new study looks at correlated variables of sea surface temperature in an isolated patch of the North Atlantic, for which we have much older records, and creates a largely linear projection of AMOC strength. Importantly, we do not know which method is correct because we don’t know if what we call “spurious variables” are at play; where the correlation between sea surface temperature in this one specific region and AMOC strength is explained by some other variable that may have no utility at all in predicting a collapse. We also aren’t sure if a collapse would be sudden, gradual or not occur at all.

This is the challenge when looking for science to inform policy. Science is a method, not a conclusion, and the uncertainty of science is almost never accurately conveyed in politics. In the absence of being able to predict the costs and benefits of policy accurately, how will policymakers know what policies are worth bearing?

The answer is that in these situations policy must be formulated based upon risk. Imagine that Mr. Smith has home insurance even though it is unlikely that his house will catch fire. Similarly, policy needs to be formulated with risk in mind. When it comes to fire risk, Smith, his insurer and building code creators seek the least-cost methods of mitigating fire risk, which reduces the overall cost and likelihood of a house fire—but Smith can never truly know if the policies did in fact prevent a house fire or not, and whether he saved money or wasted it.

Climate change should be treated similarly. In the absence of certainty about cost, we should identify low-cost policies that are very likely to deliver greater benefit than cost (a revenue-neutral carbon tax, for example), and these should be prioritized over high-cost policies that are unlikely to deliver benefits (such as the electricity subsidies in the Inflation Reduction Act).

But climate policy is not based on risk. Politicians favor dramatic language and debates over statistical versus observational scientific methods are far too tedious to motivate voters. Nevertheless, it is up to policy educators to emphasize that even when we don’t know for sure what policies are worthwhile, we can at least say where policies fit in a hierarchy of effectiveness and guide policymakers to more efficient outcomes.