In a recent “fact sheet” on the threat climate change poses to human health, the White House cherry-picked data on the estimated number of premature deaths due to future extreme temperatures:
- The White House cited a nationwide model that predicts roughly 11,000 deaths in 2030 and more than 27,000 deaths in 2100 from extreme heat exposure compared with a 1990 baseline. But it ignores another model from the same study that predicts significantly fewer premature deaths – 6,950 in 2030 and 19,509 in 2100.
- The White House also ignored that the study predicts a decrease in the number of premature deaths from extreme cold temperatures. The net number of additional deaths from extreme temperatures in the model cited by the White House are 4,665 in 2030 and 9,632 in 2100.
- The White House makes no mention of the role that future adaptation could play in reducing deaths from extreme heat, such as greater accessibility to air conditioning and increased vegetation in cities.
The April 4 fact sheet announced the Obama Administration’s release of a new report from the U.S. Global Change Research Program called “The Impacts of Climate Change on Human Health in the United States.” Established in 1989 and mandated by Congress in 1990, the USGCRP is a “confederation” of research teams from 13 federal departments and agencies, including NASA and the Environmental Protection Agency.
We’ll first address the observed trends in premature deaths due to temperature extremes. We’ll then explain what the two models cited by the USGCRP report predict for the 21st century and what scientists know about how future adaptation could reduce the number deaths due to extreme heat.
As the USGCRP’s report explains, the “U.S. average temperatures have increased by 1.3°F to 1.9°F” since 1895 due to elevated greenhouse gas emissions. Accordingly, “heat waves have become more frequent and intense, and cold waves have become less frequent across the nation.” With a 3°F to 10°F increase by 2100, scientists predict these trends will continue into the future.
Temperature extremes can lead to a greater number of premature deaths “by compromising the body’s ability to regulate its temperature,” the report says. In addition to directly causing death through hyperthermia and hypothermia, temperature extremes can also indirectly lead to death by worsening chronic conditions, such as cardiovascular and respiratory diseases.
There are two ways to quantify the number of deaths from extreme temperatures – direct attribution in medical records and statistical analysis, which correlate trends in temperature, death and other records. Medical records tend to underestimate the number deaths, while statistical techniques may overestimate mortality rates, though to a lesser degree, according to the report authors.
For example, death records from 2006 to 2010 show roughly 1,300 deaths per year from extreme cold and 670 deaths per year from extreme heat in the U.S., according to the report (pages 47, 49). However, statistical approaches have estimated more than 1,300 deaths per year in the U.S. due to extreme heat from 1975 to 2004.
Studies have also shown that Americans have been adapting to temperature extremes over time. One paper, published online in the journal Natural Hazards on June 27, 2010, looked at U.S. Census and temperature data from 1975 to 2004 and found that extreme heat-related death rates have declined since 1996.
David M. Mills, an environmental analyst at Abt Associates and one of the USGCRP report authors, and his colleagues on the 2010 paper, hypothesized that improvements in extreme heat event forecasting, notification, and response measures could be behind these reduced rates. Additional studies have pointed to other adaptations, such as increased use of air conditioning and improved health care, to explain the reduction since the 1980s and 1990s.
But adaptation has it limits. “While historically adaptation has outpaced warming, most studies project a future increase in mortality even when including assumptions regarding adaptation,” write the report authors. In the next section we’ll outline what the two abovementioned models predict for the future.
Scientists predict an increase in the “frequency and severity of future extreme heat events while also resulting in generally warmer summers and milder winters,” says the USGCRP report. One of the report’s key findings points to the effects these temperature changes will have on human health:
USGCRP, April 4: Based on present-day sensitivity to heat, an increase of thousands to tens of thousands of premature heat-related deaths in the summer … and a decrease of premature cold-related deaths in the winter … are projected each year as a result of climate change by the end of the century. Future adaptation will very likely reduce these impacts … The reduction in cold-related deaths is projected to be smaller than the increase in heat-related deaths in most regions.
Thus, in its fact sheet, the White House correctly states: “Extreme heat can be expected to cause an increase in the number of premature deaths, from thousands to tens of thousands, each summer, which will outpace projected decreases in deaths from extreme cold.”
But the White House then goes on to cherry-pick data from one model discussed in the report: “One model projected an increase, from a 1990 baseline for more than 200 American cities, of more than an additional 11,000 deaths during the summer in 2030 and more than an additional 27,000 deaths during the summer in 2100.”
The USGCRP report cites two models from a study published online in Environmental Health on Nov. 4, 2015. Compared to a 1990 baseline, one model predicts an increase of 11,646 premature deaths from extreme heat and a reduction of 6,981 deaths from extreme cold in 2030, bringing the net number of deaths due to extreme temperature to 4,664. For 2100, this model predicts an increase of 27,312 deaths from extreme heat and a reduction of 17,680 deaths from extreme cold, with the net number of deaths at 9,632.
The White House would have been more accurate if it cited this model’s net number of deaths due to extreme temperatures. But it still wouldn’t account for the second model’s less severe predictions.
The second model predicts an increase of 6,950 premature deaths from extreme heat and a decrease of 5,207 deaths from extreme cold for 2030. This brings the net number of deaths from extreme temperatures to 1,743 compared with a 1990 baseline. For 2100, the second model projects an increase of 19,509 deaths from extreme heat and a decrease of 16,468 from extreme cold, with the net number of deaths at 3,042.
It is worth noting that the USGCRP report states scientists have “high confidence” that heat deaths will increase in the future, based on agreement among “a large number of studies as well as consistency across scenarios and regions.” Since fewer studies have looked at winter mortality and some research suggests “winter mortality is not strongly linked to temperatures,” scientists have “medium confidence” that cold-related deaths will decrease in the future.
Even still, this study’s authors repeatedly note that the projections don’t account for future adaptation. And this is no small point. One of the USGCRP report’s key findings was that there is “strong evidence” to suggest that adaptation “will reduce the projected increase in deaths from heat.” Yet the White House makes no mention of this finding in its fact sheet.
However, quantifying this future reduction has proved difficult because scientists aren’t sure what kind of adaptations have the largest effect, among other factors. Though the USGCRP cites no national level predictions, some studies have looked at how certain regions or cities could adapt to increase temperatures.
One study, published online in Climatic Change on March 23, 2012, found that adaptation may reduce heat-related mortality by 37 to 56 percent in nine regions across California in the 2090s. The study, conducted by Laurence S. Kalkstein, a public health expert at the University of Miami, and others, cites both physiological and behavioral adaptations, including the body’s ability to adjust to gradual increases in temperature over time and increased access to air conditioning, respectively.
Another study, published online in PLOS ONE on June 25, 2014, found that different combinations of land surface changes, including increased vegetation and albedo (i.e. cool, reflective) building materials, could potentially “offset projected increases in heat-related mortality by 40 to 99%” in Atlanta, Philadelphia and Phoenix in 2050.
Conducted by Brian Stone Jr., an urban environmental planning expert at Georgia Tech, and others, the study notes that “heat management strategies most effective in offsetting mortality vary by region.” For example, “vegetative strategies” had “protective benefits greater than or comparable to albedo enhancement in Atlanta and Philadelphia, while albedo enhancement was found to be more protective in Phoenix.” The reason: It’s harder to maintain vegetation in Phoenix’s arid climate.
USGCRP report also notes how America’s varied climate can effect projections on premature deaths due to extreme temperatures in the future. Both above-cited models found that some “individual cities show a net reduction in future deaths due to future warming, mainly in locations where the population is already well-adapted to heat but poorly prepared for cold (like Florida).”
To sum up, the White House cherry-picked data on premature deaths from extreme temperatures in the future. Not only did its “fact sheet” on the subject solely cite results from the more extreme model, but it also failed to note future decreases in premature deaths due to milder winters and adaption.
Editor’s Note: SciCheck is made possible by a grant from the Stanton Foundation.