Research by environmental scientists at the Harvard School of Engineering and Applied Sciences (SEAS) brings bad news to the western United States, where firefighters are currently battling dozens of fires in at least 11 states.

The Harvard team's study suggests wildfire seasons by 2050 will be about three weeks longer, up to twice as smoky, and will burn a wider area in the western states. The findings are based on a set of internationally recognized climate scenarios, decades of historical meteorological data, and records of past fire activity.

Awareness is building that gradual climate change may contribute in the coming years to increases in significant, disruptive events like severe storms and floods.

In the future atmosphere we expect warmer temperatures, which are conducive to fires. It turns out that, for the western United States, the biggest driver for fires in the future is temperature, and that result appears robust. When we get a large temperature increase over time, as we are seeing, and little change in rainfall, fires will increase in size.

By examining records of past weather conditions and wildfires, the team found that the main factors influencing the spread of fires vary from region to region. In the Rocky Mountain Forest, for example, the best predictor of wildfire area in a given year is the amount of moisture in the forest floor, which depends on the temperature, rainfall, and relative humidity that season. In the Great Basin region, different factors apply. There, the area burned is influenced by the relative humidity in the previous year, which promotes fuel growth. Yue, who was a postdoctoral fellow at Harvard SEAS and is now at Yale University, created mathematical models that closely link these types of variables seasonal temperatures, relative humidity, the amount of dry fuel and so forth with the observed wildfire outcomes for six "ecoregions" in the West.

After developing those models, the team replaced the historical observations with data based on the conclusions of the fourth Intergovernmental Panel on Climate Change (IPCC), which use socioeconomic scenarios to predict possible future atmospheric and climatological conditions. For this study, the Harvard group followed the A1B scenario, which considers the climatological effect of a fast-growing global economy relying on a mixture of fossil fuels and renewable energy sources. By running the IPCC's climate data for the year 2050 through their own fire prediction models, the Harvard team was able to calculate the area burned for each ecoregion at midcentury.

For example, the calculations suggest the following for 2050 in the western United States, in comparison to present-day conditions:

• The area burned in the month of August could increase by 65% in the Pacific Northwest, and could nearly double in the Eastern Rocky Mountains/Great Plains regions and quadruple in the Rocky Mountains Forest region.
• The probability of large fires could increase by factors of 2-3.
• The start date for the fire season could be earlier (late April instead of mid-May), and the end date could be later (mid-October instead of early October).

Air quality is also projected to suffer as a result of these larger, longer-lasting wildfires. Smoke from wildfires is composed of organic and black carbon particles and can impede visibility and cause respiratory problems. The researchers predict that smoke will increase 20-100% by the 2050s, depending on the region and the type of particle.

One of the greatest uncertainties in the science of climate change is the sensitivity of surface temperatures to rising levels of greenhouse gases.

Increasing wildfires may erase some of the progress.

 Source:

http://www.sciencedaily.com/releases/2013/08/130828172957.htm