What the National Climate Assessment Doesn’t Tell You

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.”


The Obama Administration this week is set to release the latest version of the National Climate Assessment—a report which is supposed to detail the potential impacts that climate change will have on the United States.  The report overly focuses on the supposed negative impacts from climate change while largely dismissing or ignoring the positives from climate change.

The bias in the National Climate Assessment (NCA) towards pessimism (which we have previously detailed here) has implications throughout the federal regulatory process because the NCA is cited (either directly or indirectly) as a primary source for the science of climate change for justifying federal regulation aimed towards mitigating greenhouse gas emissions. Since the NCA gets it wrong, so does everyone else.

A good example of this can be found in how climate change is effecting  the human response during heat waves.  The NCA foresees an increasing frequency and magnitude of heat waves leading to growing numbers of heat-related deaths. The leading science suggests just the opposite.

Case and point. Last week, we had an article published in the peer-reviewed scientific journal Nature Climate Change that showed how the impacts of extreme heat are often overplayed while the impacts of adaptation to the heat are underplayed.  And a new paper has just been published in the journal Environmental Health Perspectives that finds that the risk of dying from heat waves in the U.S. has been on the decline for the past several decades.

By now, this should be rather unsurprising as it has been demonstrated over and over again. Not only in the U.S. but in Europe (and yes, Stockholm) and other major global cities as well. 

The idea that human-caused global warming is going to increase heat-related mortality is simply outdated and wrong. In fact, the opposite is more likely the case—that is, a warming climate will decrease the population’s sensitivity to heat events as it induces adaptation.  We described it this way in our Nature Climate Change piece:

Some portion of this response [the decline in the risk of dying from heat waves] probably reflects the temporal increase in the frequency of extreme-heat events, an increase that elevates public consciousness and spurs adaptive response. In this manner, climate change itself leads to adaptation.

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

But this information often falls on deaf ears—especially those ears responsible for developing the NCA.

Here is what the Executive Summary of the draft version had to say about heat-related mortality:

Climate change will influence human health in many ways; some existing health threats will intensify, and new health threats will emerge. Some of the key drivers of health impacts include: increasingly frequent and intense extreme heat, which causes heat-related illnesses and deaths and over time, worsens drought and wildfire risks, and intensifies air pollution.

The U.S. Environmental Protection Agency takes the same outlook (of course since it is based heavily on the National Climate Assessment).  The EPA leaned heavily on heat-related mortality as one the “threats” to public health and welfare in its justification for pursuing greenhouse gas emissions restrictions. From the EPA’s Technical Support Document for its greenhouse gas “Endangerment Finding”:

Severe heat waves are projected to intensify in magnitude and duration over the portions of the United States where these events already occur, with potential increases in mortality and morbidity, especially among the elderly, young, and frail. [emphasis in original]

Now compare the Administration’s take with the latest findings on the trend in heat-related mortality across the United States as published by a research team led by Harvard School of Public Health’s Jennifer Bobb.   Bobb and colleagues found that the risk of dying from excessive heat events was declining across the U.S. And further, that most of the overall decline was coming from declines in the sensitivity to extreme heat shown by the elderly population (75 and older).  In fact, the Bobb team found that the risk in the older population has dropped so far that it is now indistinguishable from the risk to the younger populations. Adaptation is a beautiful thing!

From Bobb et al.:

While heat-related mortality risk for the ≥75 age group was greater than for the <65 group at the beginning of the study period, by 2005 they had converged to similar levels.

In other words, all the EPA’s talk about an increasing threat from heat waves and a growing elderly population combining to negatively impact the public health and welfare has been wrong up to now and almost assuredly will be so into the future as we continually look for ways to avoid dying avoidable deaths (e.g., those from heat waves).

Bobb and colleagues summarize this way:

This study provides strong evidence that acute (e.g., same-day) heat-related mortality risk has declined over time in the US, even in more recent years. This evidence complements findings from US studies using earlier data from the 1960s through mid-1990s on community-specific mortality rates (Davis et al. 2003a; Davis et al. 2003b), as well as European studies that found temporal declines in heat-related mortality risk (Carson et al. 2006; Donaldson et al. 2003; Kysely and Plavcova 2011; Schifano et al. 2012), and supports the hypothesis that the population is continually adapting to heat.

As a note, we (Knappenberger and Michaels) were co-authors on the two Davis et al. studies cited in the above paragraph. Our work, first published more than a decade ago, was some of the first research into the declining trends in heat-related mortality across the U.S.

Clearly we have been saying all this stuff for a long time and even more clearly, the federal government hasn’t been listening for a long time. It is not what they want to hear.

References:

Bobb, J.F., R.D. Peng, M.L. Bell, and F. Dominici, 2014. Heat-related mortality and adaptation in the United States, Environmental Health Perspectiveshttp://dx.doi.org/10.1289/ehp.1307392

Davis, R.E., P.C. Knappenbergre, P.J. Michaels, and W.M. Novicoff, 2003a, Changing heat-related mortality in the United States. Environmental Health Perspectives111, 1712–1718.

Davis, R.E., P.C. Knappenbergre, P.J. Michaels, and W.M. Novicoff, 2003b, Decadal changes in summer mortality in U.S. cities. International Journal of Biometeorology, 47, 166–75.

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