What The National Climate Assessment Doesn’t Tell You

  • Date: 07/05/14
  • Paul C. "Chip" Knappenberger and Patrick J. Michaels, Cato Institute

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 journalNature 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The idea that human-caused global warming is going to increase heat-related mortality is simply outdated and wrong.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!

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