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Loaded Dice and Human Health: Measuring the Impacts of Climate Change
April 24, 2012 By Stuart KentIn a new article in the Proceedings of the National Academy of Sciences (PNAS), “Insights From Past Millennia Into Climatic Impacts on Human Health and Survival,” Anthony McMichael compares scientific literature that reconstructs past climates with epidemiological research and comes away with more than a dozen examples of the influence of climate on human health and survival. “Risks to health [as a result of climatic change] are neither widely nor fully recognized,” McMichael writes, but “weather extremes and climatic impacts on food yields, fresh water, infectious diseases, conflict, and displacement” have led to human suffering across the centuries. Some of the literature reviewed, for instance, links the Younger Dryas (a several centuries long period of cooling) to hunger in the Nile Valley between 11,000 and 12,000 years ago, climatic shifts that expanded the range of disease carrying rats and fleas to the “Black Death” during the mid-1400s, and unusually strong El Niño events to a series of late Victorian-era droughts during the late-1800s.
“Climate Variability and Climate Change: The New Climate Dice,” a working paper from James Hansen, Makiko Sato, and Reto Ruedy recently submitted to PNAS, uses surface air temperature analysis from the Goddard Institute for Space Studies to examine the impact of global warming on the frequency of extreme weather events. Using measurements from 1951 to 1980 as a baseline, the study finds, first, that the planet has warmed by around half of a degree Celsius since the reference period, and second, that the global area affected by “extreme anomalies” (exceeding three standard deviations from the mean climate) has increased by a factor greater than 10. Affecting approximately 10 percent of global land surface in the last several years, these anomalies, such as the droughts and heat waves observed in Texas in 2011, Moscow in 2010, and France in 2003, “almost certainly would not have occurred in the absence of the global warming,” according to the authors.
The study uses this new evidence about the impact of climate change to update the concept of climate change as a “loading of the climate dice.” Where, the “climate of 1951-1980 [is represented] by colored dice with two sides red for ‘hot,’ two side blue for ‘cold,’ and two sides white for near average temperature,” and the dice themselves represent the chance of observing variations on mean temperature. Under this metaphor, today’s climate is best approximated by a dice with four sides red, one blue, and one white, according to the study.
As for the future, the data suggest that with just one full degree of warming, anomalies three deviations beyond the mean will be the norm, and five deviations beyond the mean will become more likely (the latest IPCC projections suggest between 1.8 and 4.0 degrees Celsius are likely). In essence, the red side of the die are not only multiplying, but becoming much more extreme. To put this into scale, the Moscow 2010 heat wave, an event that exceeded the three deviations mark, coincided with a doubling of the death rate in the Russian capital.
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