Heat-related Death Projections Don’t Square with Observations

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.”

We realize that we are 180° out of sync with the news cycle when we discuss heat-related death in the middle of Northern Hemisphere winter, but we’ve come across a recent paper that can’t wait for the heat and hype of next summer.

The paper, by Arizona State University’s David Hondula and colleagues, is a review of the recent scientific literature on “human health impacts of observed and projected increases in summer temperature.”

This topic is near and dear to our hearts, as we have ourselves contributed many papers to the scientific literature on this matter (see here).  We are especially interested in seeing how the literature has evolved over the past several years and Hondula and colleagues’ paper, which specifically looked at findings published in the 2012-2015 timeframe, fills this interest nicely.

Here’s how they summed up their analysis:

We find that studies based on projected changes in climate indicate substantial increases in heat-related mortality and morbidity in the future, while observational studies based on historical climate and health records show a decrease in negative impacts during recent warming. The discrepancy between the two groups of studies generally involves how well and how quickly humans can adapt to changes in climate via physiological, behavioral, infrastructural, and/or technological adaptation, and how such adaptation is quantified.

Did you get that? When assessing what actually happens to heat-related mortality rates in the face of rising temperatures, researchers find that “negative impacts” decline. But, when researchers attempt to project the impacts of rising temperature in the future on heat-related mortality, they predict “substantial increases.”

In other words, in the real world, people adapt to changing climate conditions (e.g., rising temperatures), but in the modeled world of the future, adaptation can’t keep up. 

But rather than assert this as a problem with model world behavior that needs serious attention, most assessments of the projected impacts of climate change (such as the one produced by our federal government as a foundation for its greenhouse gas mitigation policies) embrace model world forecasts and run with storylines like “global warming set to greatly increase deaths from heat waves.”

We’ve been railing against this fact for years. But, it never seems gain any traction with federal climatologists.

Interestingly, in all the literature surveyed by Hondula’s group, they cite only one study which suggested that climate change itself may be aiding and abetting the adaptive processes. The idea forwarded in that study was that since people adapt to heat waves, and since global warming may be, in part, leading to more heat waves, that global warming itself may be helping to drive the adaptive response.  Rather than leading to more heat-related deaths, global warming may actually be leading to fewer.

Who were the authors of that study? Perhaps they may by familiar to you: Chip Knappenberger, Pat Michaels, and Anthony Watts.

While Hondula and colleagues seem to be amenable to our premise, they point out that putting an actual magnitude on this effect is difficult:

If changing climate is itself a modifier of the relationship between temperature and mortality (e.g., increasing heat wave frequency or severity leads to increasing public awareness and preventative measures), a quantitative approach for disentangling these effects has yet to be established.

We concur with this, but, as we point out in our paper using the history of heat-related mortality in Stockholm as an example, it doesn’t take much of a positive influence from climate change to offset any negatives:

[R]aised awareness from climate change need only be responsible for 288 out of 2,304 (~13%) deaths saved through adaptation to have completely offset the climate-related increase in heat-related mortality [there].  For any greater contribution, climate change would have resulted in an overall decline in heat-related mortality in Stockholm County despite an increase in the frequency of extreme-heat events.

We went on to say (in somewhat of an understatement):

Our analysis highlights one of the many often overlooked intricacies of the human response to climate change.

Hondula’s team adds this, from their conclusion:

By directing our research efforts to best understand how reduction in heat mortality and morbidity can be achieved, we have the opportunity to improve societal welfare and eliminate unnecessary health consequences of extreme weather—even in a hotter future.

Well said.


Hondula, D. M., R. C. Balling, J. K. Vanos, and M. Georgescu, 2015. Rising temperatures, human health, and the role of adaptation. Current Climate Change Reports, 1, 144-154.

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