PNAS has struck again. That’s the Proceedings of the National Academy of Sciences, which, according to bibliographic metrics, is the second‐most influential science journal published in the U.S. Science, from the American Association for the Advancement of Science, is in first place.
As I have discussed previously (http://www.forbes.com/sites/patrickmichaels/2011/06/16/peer-review-and-…) the procedures for publishing in PNAS are not those typically associated with rigorous peer‐review, and much more resemble “pal review”. As a result, sometimes some rather strange papers appear.
A textbook example is this paper by Antonella Zanobetti, Marie O’Neill, Carina Gronlund, and Joel Schwartz.
Zanobetti, from Harvard, and her colleagues attempt to answer the question as to whether or not summer temperature variability—not temperature itself—is associated with an increase in mortality in elderly people with chronic disease.
While the accepted wisdom is that heat waves can lead to elevated mortality (for those unprepared), what is not so widely known, but nonetheless obvious to those who think in economic terms, is that the more frequent high temperature extremes are, the lower the overall rate of heat‐related mortality becomes. Pure and simple, people adapt.
(The EPA, in its zeal to regulate carbon dioxide, has it completely wrong on this association, claiming that increased heat wave frequency and magnitude constitute endangerment to the public health and welfare, when, in actuality, the data clearly show that more heat leads to a lower heat‐related morality rate.)
This is obvious from Figure 1, which is taken from some heat‐related mortality research that I was involved in (Davis et al., 2003). The heat‐related mortality rate in each of 28 cities across the country for three different decades (1970s, 1980s, 1990s) is represented in Figure 1 by a set of three bars plotted at each city’s location on the map. The higher the bars, the greater the heat‐related mortality.
Note that the cities along the southern tier of the U.S.—the ones with the hottest summers—have much lower rates of heat‐related mortality than do the cooler cities in the Midwestern and Northeastern parts of the country. Where people are used to very high temperatures, they are adept at dealing with them. In the Midwest and the Northeast, where heat waves are rare, more people die.
Note also that the height of the bars in virtually every city is declining with time. In other words, more people died from heat waves in the 1970s than did so in the 1990s—in spite of generally rising summer time temperatures during that period (the mortality trend is indicated by the “+” or “-“ sign below each set of bars). In fact, in many cities across the southern and central portion of the country, there is no bar at all during the 1990s, indicating that heat‐related mortality was statistically undetectable during that decade. Taken as a whole, the heat‐related mortality in major U.S. cities declined by 75% across the last decades of the 20th century, despite rising summer temperatures. Clearly, we are adapting well to increased frequency and intensity of heat waves.
The one exception, which proves the adaptational rule, is Seattle—which has the coolest average summers and shows an increase in mortality.
Figure 1. Annual heat‐related mortality rates (excess deaths per standard million population on days in which the decadal‐varying threshold apparent temperature (AT) is equaled or exceeded) by city and decade, and long‐term trend in summer afternoon AT. Each histogram bar indicates a different decade: from left to right, 1960s‐1970s, 1980–1989, and 1990–1998. Decades without histogram bars exhibit no threshold ATs and no heat‐related mortality. Decades with gray bars have mortality rates that are statistically significantly different from the decades indicated by black bars. The average excess deaths across all 28 cities is shown at the lower left. AT trends are indicated beneath each city abbreviation (Davis et al., 2003).
But there were some interesting questions raised concerning the interpretation of our results—in particular, about the role of temperature variability in shaping our findings. We noted (Davis et al., 2003):