Stanford scientist produces first-ever study linking increased mortality specifically to carbon dioxide emissions

http://news-service.stanford.edu/news/2008/january9/co-010908.html

A Stanford scientist has spelled out for the first time the direct links between increased levels of carbon dioxide in the atmosphere and increases in human mortality, using a state-of-the-art computer model of the atmosphere that incorporates scores of physical and chemical environmental processes. The new findings, to be published in Geophysical Research Letters, come to light just after the Environmental Protection Agency's recent ruling against states setting specific emission standards for this greenhouse gas based in part on the lack of data showing the link between carbon dioxide emissions and their health effects.

While it has long been known that carbon dioxide emissions contribute to climate change, the new study details how for each increase of 1 degree Celsius caused by carbon dioxide, the resulting air pollution would lead annually to about a thousand additional deaths and many more cases of respiratory illness and asthma in the United States, according to the paper by Mark Jacobson, a professor of civil and environmental engineering at Stanford. Worldwide, upward of 20,000 air-pollution-related deaths per year per degree Celsius may be due to this greenhouse gas.

"This is a cause and effect relationship, not just a correlation," said Jacobson of his study, which on Dec. 24 was accepted for publication in Geophysical Research Letters. "The study is the first specifically to isolate carbon dioxide's effect from that of other global-warming agents and to find quantitatively that chemical and meteorological changes due to carbon dioxide itself increase mortality due to increased ozone, particles and carcinogens in the air."

For this study, Jacobson used the computer model to determine the amounts of ozone and airborne particles that result from temperature increases caused by increases in carbon dioxide emissions. Ozone causes and worsens respiratory and cardiovascular illnesses, emphysema and asthma, and many published studies have associated increased ozone with higher mortality. "[Ozone] is a very corrosive gas; it erodes rubber and statues," Jacobson said. "It cracks tires. So you can imagine what it does to your lungs in high enough concentrations." Particles are responsible for cardiovascular and respiratory illness and asthma.

Jacobson simultaneously calculated the effects of increasing temperatures on pollution. He observed two important effects:

Higher temperatures due to carbon dioxide increased the chemical rate of ozone production in urban areas.
Increased water vapor due to carbon dioxide-induced higher temperatures boosted chemical ozone production even more in urban areas.
Interestingly, neither effect was so important under the low-pollution conditions typical of rural regions, though other factors, such as higher organic gas emissions from vegetation, affected ozone in low-pollution areas. Higher emissions of organic gases also increased the quantity of particles in the air, as organic gases can chemically react to form particles.

And in general, where there was an increase in water vapor, particles that were present became more deadly, as they swelled from absorption of water. "That added moisture allows other gases to dissolve in the particles—certain acid gases, like nitric acid, sulfuric acid and hydrochloric acid," Jacobson said. That increases the toxicity of the particles, which are already a harmful component of air pollution.

Jacobson also found that air temperatures rose more rapidly due to carbon dioxide than did ground temperatures, changing the vertical temperature profile, which decreased pollution dispersion, thereby concentrating particles near where they formed.