Science vs. Expert Opinion: Did the Bush Administration Really Censor Science? |
| Written by Paul Georgia | |
| Wednesday, 14 November 2007 | |
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Science vs. Expert Opinion Introduction Once again, the press is in a tizzy over the Bush Administration’s “censoring of science.” The case against the Bush Administration this time is that it edited testimony presented to the Senate Environment and Public Works Committee (EPW) by Julie Gerberding, director of the Centers for Disease Control and Prevention (CDC). The testimony, originally 14 pages, was cut to six. However, the narrative of a scientific cover-up is overwrought to say the least. The hearing was on the potential impact of global warming on human health, an exercise in speculation. It appears, if press accounts are correct, that what the Bush Administration cut from the director’s testimony was more speculation than settled science. When judging scientific statements, one must distinguish between statements of what has happened or is happening and those about what might happen in the future. The first is derived from observation, an important component of the scientific method. The second is derived from expert opinion, a far less reliable source of knowledge, and one only tenuously linked to actual science. ABC News claimed that Gerberding’s pre-edited testimony argued that climate change would lead to “heat waves, cold spells, extreme weather events and weather disasters, air pollution, increased infectious diseases, and increased waterborne and vector-borne infectious diseases.” According to an account of the hearing by Fox News, Senator Barbara Boxer, EPW committee chairman, “produced a CDC chart listing the broad range of health problems that could emerge from a significant temperature increase and sea level rise. They include fatalities from heat stress and heart failure, increased injuries and deaths from severe weather such as hurricanes; more respiratory problems from drought-driven air pollution; an increase in waterborne diseases including cholera, and increases in vector-borne diseases including malaria and hantavirus; and mental health problems such as depression and post-traumatic stress.” When asked about this, Gerberding agreed, “These are potential things you can expect. In some of these areas its not a question of if, it’s a question of who, what, how and when.” But what is the basis for these claims? Does the CDC have evidence of a link between past climate change and harm to human health? After all, levels of greenhouse gases in the atmosphere are already three-quarters of the way towards an effective doubling of carbon dioxide concentrations, the benchmark typically used in making global warming predictions. And the global average temperature has risen. If global warming predictions are true, and such a link exists, then the harms mentioned by Senator Boxer should already be evident in the data. However, the data fail to reveal such a link. In reality, the list of horrors provided by Senator Boxer is little more than speculation based on the opinion of a few experts, not on science. The following sections review the available data on each of the harms mentioned. In each case, the harms to human health with respect to various climate indicators seem to be decreasing. Heat-Related Mortality Presumably, rising global temperature would harm human health by increasing the frequency and intensity of heat waves, which can be fatal. But has heat-related morality risen in the U.S. in response to rising global temperature? The answer seems to be no. A study of 28 major U.S. cities found that in nearly every case, the population’s sensitivity to extremely high temperatures has been declining over time despite a general rise in summertime temperatures (Davis, et al., 2003). This desensitization is attributed to better medical practices, increased access to air-conditioning, and improved community response programs. In some cities, by the 1990s, heat-related mortality was virtually non-existent.  Figure 1. Annual average excess summer mortality due to high temperatures, broken down by decade, for 28 major cities across the United States. For each city each of the three bars represents the average mortality during successive decades (left bar 1964-66 + 1973-1979; middle bar 1980-1989, right bar 1990-1998). The bottom-left shows the 28-city average (taken from Davis et al., 2003). Infectious Disease There is little evidence of a link between climate change and insect- or rodent-borne disease, despite claims to the contrary. In the following sections we review some of the historical data on infectious disease and its relationship to climate. Rodent-Borne Disease Much has been made of the 1993 Hantavirus outbreak in the Four Corners area of the United States. Proponents of the disease/climate-change link have used the rodent-borne outbreak to illustrate that even minor climatic changes can have deadly effects. As noted in a study on the outbreak, It has been hypothesized that the El Niño Southern Oscillation (ENSO) of 1991-92 was the major climatic factor producing environmental conditions leading to the outbreak of HPS in 1993. Unseasonable rains in 1991 and 1992 during the usually dry spring and summer and the mild winter of 1992 are thought to have created favorable conditions for an increase in local rodent populations. Those conditions were increased vegetation growth favorable to rodents. However, when the researchers analyzed precipitation data from 196 weather stations throughout the region from 1986 to 1993, they found that, “None of the case sites had higher precipitation during 1992 to 1993 than during the preceding 6 years.”  Figure 2. March-June precipitation patterns at case sites (solid symbols) and control sites (open symbols) from 1986 through 1993. Vertical bars are 1 standard deviation in precipitation values (Glass, et al., 2000). Moreover, the researchers could not find a consistent association between vegetation growth and risk for hantavirus. They conclude, “The hypothesized pathway between ENSO, increased spring precipitation leading to increased vegetation growth, and subsequent HPS risk, however, was not strongly supported by the data.” The studies further conclude: Additionally, although the reason to assume a relationship between climate variability and infectious disease outbreaks is clear, few studies have evaluated whether this presumed relationship actually exists. This study indicates that if these relationships do occur, they are modulated by a number of poorly understood ecologic and social conditions that will require substantial detailed studies of the pathways influencing disease risk. Insect-Borne Disease In a review of the history of malaria, Paul Reiter (2000), an expert on insect-borne disease, noted that, Until the second half of the 20th century, malaria was endemic and widespread in many temperate regions, with major epidemics as far north as the Arctic Circle. From 1564 to the 1730s—the coldest period of the Little Ice Age—malaria was an important cause of illness and death in several parts of England. Transmission began to decline only in the 19th century, when the present warming trend was well under way. The history of the disease in England underscores the role of factors other than temperature in malaria transmission. In another study by Reiter (2001), he noted that, The histories of…malaria, yellow fever, and dengue, reveal that climate has rarely been the principal determinant of their prevalence or range; human activities and their impact on local ecology have generally been much more significant. It is therefore inappropriate to use climate-based models to predict future prevalence.One example of how factors other than climate play a dominant role in determining the risk from infectious disease comes from data on the prevalence of dengue fever along the Texas/Mexico border. From 1980 to 1999, 62,514 suspected cases of dengue fever were reported in the Mexican border states of Coahuila, Nuevo Leon, and Tamaulipas. However, only 64 cases were reported in Texas during the same timeframe. This was the case despite substantial border crossings. In 1997 alone, U.S. immigration authorities reported nearly 70 million personal crossings from those three Mexican states into Texas.  Figure 3. Dengue was once common in Texas (where there were an estimated 500,000 cases in 1922), and the mosquito that transmits it remains abundant. The striking contrast in the incidence of dengue in Texas versus three Mexican states that border Texas (43 cases vs. 50,333) in the period from 1980-1996 provides a graphic illustration of the importance of factors other than temperature (U.S. Global Change Research Program). Additional Climate Indicators Senator Boxer’s CDC chart also mentioned several other supposed dangers from global warming. But again, there is little in the way of empirical data to support these speculations. These include: • Pollution: Ground-level ozone levels are influenced by temperature. The warmer the temperature, the more likely ozone-forming substances, such as volatile organic compounds will combine to form ozone. However, despite an increase in U.S. summertime temperatures from 1980 to 2006, ground-level ozone has fallen substantially (Environmental Protection Agency, 2007). • Hurricanes: There are no trends in hurricane damages due to Atlantic hurricanes in the U.S. over the last century (Pielke, 2006). • Tornadoes: Tornado deaths in the U.S. have fallen throughout the century (http://www.hprcc.unl.edu/nebraska/us-tornado-deaths1916-2004.html). • Drought: There is no evidence of an increase in the frequency of dry spells in the U.S. over the last century (National Climate Data Center, 2007). • Floods: There is no evidence of an increase in the frequency of wet spells in the U.S. over the last century (National Climate Data Center, 2007). Moreover, flood damages in the U.S. have fallen over the last several decades (Pielke, 2006). Conclusion The claim that the Bush Administration is censoring “science” is without merit. What the Administration seems to have done is cut the portions of the testimony that were backed up by little more than expert speculation. While many are impressed by expert opinion, it doesn’t rise to the level of scientific rigor necessary to make important policy decisions. A new paper by Professors Scott Armstrong and Kesten Green (2007), leading experts on forecasting, shows that expert opinion is notoriously unreliable. “Comparative empirical studies have routinely concluded that judgmental forecasting by experts [rather than scientific forecasting] is the least accurate of the methods available to make forecasts.” They also show that, “Agreement among experts is weakly related to accuracy,” when it comes to forecasting. The media has the storyline exactly backwards. Rather than censoring science, the Bush Administration acted responsibly by removing baseless speculation from the CDC’s testimony. If the purpose of congressional hearings is “fact finding,” then such speculation is inappropriate and the Administration’s actions were the only responsible course. References: Armstrong, J.S. and Green, K.C. (2007), “Global Warming: Forecasts by Scientists versus Scientific Forecasts,” forthcoming in Energy & Environment. Davis, R.E., et al. (2003). Changing heat-related mortality in the United States. Environmental Health Perspectives, 111, 1712-1718. Environmental Protection Agency (2007), “National Trends in Ozone Levels,” Air Trends. Glass, G.E. et al. (2000), “Using Remotely Sensed Data To Identify Areas at Risk for Hantavirus Pulmonary Syndrome,” Emerging Infectious Diseases, 6(3): 238-247. National Climate Data Center (2006), “U.S. Drought,” Climate of 2006: Annual Review. Pielke, R., Jr. (2006), “Disasters, Death, and Destruction: Making Sense of Recent Catastrophes,” Oceanography 19(2): 138-147. Reiter, P. (2000), “From Shakespeare to Defoe: Malaria in England in the Little Ice Age,” Emerging Infectious Diseases, 6(1): 1-11. Reiter, P. (2001), “Climate Change and Mosquito-Borne Disease,” Environmental Health Perspectives, 109(Supplement 1): 141-161. |