Adaptation to Extreme Heat

Global Science Report is a feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

Last fall, the press pounced on the results of a new study that found that global climate change was leading to an increasing frequency of heat waves and thus resulting in greater heat-related mortality. Finally a scientific study showing that global warming is killing us after all! See all you climate change optimists have been wrong all along, human-caused global warming is a threat to our health and welfare.

Not so fast.

Upon closer inspection, it turns out that the authors of that study—which examined heat-related mortality in Stockholm, Sweden—failed to include the impacts of adaptation in their analysis as well as the possibility that some of the temperature rise which has taken place in Stockholm is not from “global” climate change but rather local and regional processes not at all related to human greenhouse gas emissions.

What the researchers Daniel Oustin Åström and his colleagues left out of their original analysis, we (Chip Knappenberger, Pat Michaels, and Anthony Watts) factored in. And when we did so, we arrived at the distinct possibility that global warming actually led to a reduction in the rate of heat-related mortality in Stockholm.

Our findings have just been published in the scientific journal Nature Climate Change as a Comment on the original Oustin Åström paper (which was published in the same journal).

We were immediately skeptical because the original Oustin Åström results run contrary to a solid body of scientific evidence (including our own) that shows that heat-related mortality and the population’s sensitivity to heat waves was been declining in major cities across America and Europe as people take adaptive measures to protect themselves from the rising heat.

Contrarily, Oudin Åström reported that as a result of an increase in the number of heat waves occurring in Stockholm, more people died from extreme heat during the latter portion of the 20th century than would have had the climate of Stockholm been similar to what it was in the early part of the 20th century—a time during which fewer heat waves were recorded. The implication was that global warming from increasing human greenhouse gas emissions was killing people from increased heat.

But the variability in the climate of Stockholm is a product of much more than human greenhouse gas emissions. Variations in the natural patterns of regional-scale atmospheric circulation, such as the Atlantic Multidecadal Oscillation (AMO), as well as local impacts associated with urbanization and environmental changes in the direct vicinity of the thermometer are reflected in the city’s temperature history, and the original Oudin Åström et al. publication did not take this into account. This effect is potentially significant as Stockholm is one of Europe’s fastest growing cities.

But regardless of the cause, rising temperatures spur adaptation. Expanded use of air conditioning, biophysical changes, behavior modification, and community awareness programs are all examples of actions which take place to make us better protected from the dangers associated with heat waves. Additionally, better medical practices, building practices, etc. have further reduced heat-related stress and mortality over the years.

The net result is that as result of the combination of all the adaptive measures that have taken place over the course of the 20th century in Stockholm, on average people currently die in heat waves at a rate four times less than they did during the beginning of the 20th century. The effect of adaptation overwhelms the effect of an increase in the number of heat waves.

In fact, it is not a stretch to say that much of the adaptation has likely occurred because of an increased frequency of heat waves. As heat waves become more common, the better adapted to them the population becomes.

Our analysis highlights one of the often overlooked intricacies of the human response to climate change—the fact that the response to climate change can actually improve public health and welfare.

Which, by the way, is a completely different view than the one taken by the current Administration.

References:

Knappenberger, P., Michaels, P., and A. Watts, 2014. Adaptation to extreme heat in Stockholm County, Sweden. Nature Climate Change, 4, 302-303.

Oudin Åström, D., Forsberg, B., Ebi, K. L. & Rocklöv, J., 2013. Attributing mortality from extreme temperatures to climate change in Stockholm, Sweden. Nature Climate Change, 3, 1050–1054.