By 2055, wildfires in the western United States could scorch about 50% more land than they do now, causing a sharp decline in the region’s air quality, according to a new study by atmospheric researchers at Harvard. This potential leap in destructiveness and pollution—mainly from an increase in wildfire frequency—is forecast by computer models calculating impacts of moderate global warming on western US wildfire patterns and atmospheric chemistry.
The models show the greatest future increases in area burned (75 to 175%) in the forests of the Pacific Northwest and the Rocky Mountains. And, because of extra burning throughout the western US, one important type of smoke particle—organic carbon aerosols—would increase, on average, by about 40% during the roughly half-century period, they add.
Previous studies by other researchers have probed the links between climate change and fire severity in the West and elsewhere. However, the Harvard study represents the first attempt to quantify the impact of future wildfires on the air we breathe, says Jennifer Logan of Harvard’s School of Engineering and Applied Sciences (SEAS), who led the research. A report on the results has been accepted for publication in the Journal of Geophysical Research - Atmospheres, a journal of the American Geophysical Union (AGU).
Warmer temperatures can dry out underbrush, leading to a more serious conflagration once a fire is started by lightning or human activity. Because smoke and other particles from fires adversely affect air quality, an increase in wildfires could have large impacts on human health.—Jennifer Logan
To conduct the research, the team first examined a 25-year record of observed meteorology and fire statistics to identify those meteorological factors that could best predict area burned for each ecosystem in the western United States. To see how these meteorological factors would change in the future, the researchers then next ran a global climate model out to 2055, following a scenario of future greenhouse gas emissions known as A1B.
This scenario, one of several devised by the United Nations Intergovernmental Panel on Climate Change, describes a future world with rapid economic growth and balanced energy generation from fossil and alternative fuels. Relative to the other scenarios, it leads to a moderate warming of the earth’s average surface temperature, about 1.6 degrees Celsius (3 degrees Fahrenheit) by 2050.
By hypothesizing that the same relationships between meteorology and area burned still hold in the future, we then could predict wildfire activity and emissions from 2000 to the 2050s.—Jennifer Logan
As a last step, the researchers used an atmospheric chemistry model to understand how the change in wildfire activity would affect air quality. This model, combining their predictions of areas burned with projected 2050s meteorology data, shows the quantities of emissions and the fates of smoke and other particles released by the future wildfires. The resulting diminished air quality could lead to smoggier skies and adversely affect those suffering from lung and heart conditions such as asthma and chronic bronchitis.
Such consequences are a climate penalty that diminishes the effectiveness of efforts to reduce air pollution across the United States, the researchers say. Their new work could help policymakers gauge how severe that penalty might become. In addition, the study underscores the need for a vigorous fire management plan.
The team next plans to focus on future wildfires and air quality over the densely populated areas in California and in the southwest United States.
Logan’s collaborators include Research Associate Loretta Mickley and former postdocs Dominick Spracklen and Rynda Hudman, all at SEAS. Grants from the STAR (Science to Achieve Results) program of the National Center for Environmental Research of the US Environmental Protection Agency and from NASA supported this research.
D. V. Spracklen, L. J. Mickley, J. A. Logan. R. C. Hudman, R. Yevich, M. D. Flannigan, and A. L. Westerling (2009) Impacts of climate change from 2000 to 2050 on wildfire activity and carbonaceous aerosol concentrations in the western United States, J. Geophys. Res., In press