Climate Change Linked to Human Mortality
Scitizen interviews Dr. Mark Jacobson, whose recent study demonstrates a cause-effect relationship between increased levels of carbon dioxide and increase in human mortality. Jacobson's work stands apart from previous research in that it uses a computer model of the atmosphere that takes into account many feedbacks between climate change and air pollution not considered in previous studies.
I first demonstrated with an exact numerical solution to photochemical equations that, when ozone is already high, increases in temperature and water vapor independently increase ozone further. At low ozone, temperature has little effect on ozone, and water vapor either causes little change or decreases ozone slightly.
Following this demonstration, I solved the same chemical equations together with many other processes in a 3-D nested global-through-regional-scale climate-air pollution model, which, starting in 2000, was the first such model worldwide to treat air pollution, weather, and climate simultaneously on all scales. The model was used to show by cause and effect whether carbon dioxide alone affected air pollution. Only a model can show cause and effect since atmospheric data show correlation only (e.g., it is not possible to determine, just from data of temperatures and air pollution, and carbon dioxide whether the carbon dioxide is increasing the temperatures or air pollution - this can be shown only by a model based on physical and chemical principles. This model has been evaluated rigorously against atmospheric data.
The model found that CO2 alone increased temperatures and water vapor, and both resulted in increases in ozone as well as particulate matter, Particulate matter increased due to reduced dispersion caused by warmer temperatures, increased particle swelling due to higher humidity that allowed acid gases to dissolve more in particles, and increased emissions of organic gases from vegetation due to higher temperatures that converted to sticky gases that condensed onto particles.
Population and health statistic data were then combined with concentration changes from the model to determine the net effect of CO2 on air pollution mortality, hospitalization, asthma, and cancer.
This was then the first study to isolate the effect of carbon dioxide (as opposed to all greenhouse gases) on air pollution, the first to quantify the air pollution health effects of carbon dioxide, and the first to use a nested global-regional model to study this issue (previous studies of the effects of global warming on air pollution used either a global model only, which is too coarse or a regional model only, which does not allow realistic temperature change estimates).
2. How can these results influence policymaking?
The study shows that global warming increases air pollution the most in places that are already polluted. California is home to 6 of the 10 most polluted cities in the U.S. and suffers over 30% of the additional mortality although it has only 12% of the population. Since the U.S. Environmental Protection Agency (EPA) recently decided to deny California's request to control CO2 emissions on its own based in part on the theory that California does not suffer more than other states due to global warming, and this contention is contradicted by the study, I believe EPA should correct their decision, as it was based on a lack of information that is now available. The EPA also cited a lack of studies quantifying the health effects of CO2 due to air pollution, and this study does just that as well.
In general, this study provides a basis for regulators to control carbon dioxide based on health grounds.
Interview by Audrey Wang
1. Jacobson, M. Z. (2008), On the causal link between carbon dioxide and air pollution mortality, Geophysical. Research Letters, doi:10.1029/2007GL031101, in press. PDF available here.