November 28, 2006

Fires Dampen Warming Scare

Filed under: Climate History

This entire global warming – greenhouse effect crusade really got into high gear back in the summer of 1988. In case you have forgotten, that spring and early summer in the United States was unusually hot and dry, and on June 23rd, James Hansen (then director of NASA’s Goddard Institute for Space Studies) reported at a Senate hearing that the world was warmer than at any time in the instrumental record and he was “99 percent certain” that some of that warming was related the buildup of greenhouse gases. Following that pronouncement, the issue seemed to gather traction, and the greenhouse train got rolling down the tracks. Once that train got out of the station in 1988, it has been gaining momentum, and with the recent election results in the United States, the train is moving faster than ever.

If anyone doubted global warming back in 1988, two other events of that summer put the nail in the coffin. Remember Hurricane Gilbert? As this storm approached the Yucatán, the central pressure fell to 885 millibars, the lowest ever recorded in a Western Hemisphere storm. Hypercanes became embraced as part of the greenhouse storyline. Meanwhile, Yellowstone Park went up in flames, as did millions of acres throughout the United States. Immediately, wildfires were claimed as further evidence of global warming, and since that time, every popular presentation of the horrors of global warming includes images of wildfires.

As time passed since 1988, the scientific literature grew rapidly on warming and wildfires – obviously, a warmer world will have higher evapotranspiration rates and in the absence of increases in precipitation, ecosystems will become drier and more susceptible to wildfires. Some scientists further argued that fires could increase global warming by adding more carbon dioxide to the atmosphere, by depositing black carbon aerosols on otherwise light surfaces, and by altering the surface energy budget in the burn area where dark surfaces would increase absorbed solar radiation. Wildfires get worse as the world warms, and wildfires produce a feedback that magnifies the warming – what a perfect horror story.

A paper in the recent issue of Science has a final sentence in the abstract stating that the “result implies that future increases in boreal fire may not accelerate climate warming.” This immediately attracted our attention at World Climate Report, and with further reading, we found that the work by the large Randerson et al. team focuses on forest fires in high latitude boreal regions. The team reports on “measurements and analysis of a boreal forest fire, integrating the effects of greenhouse gases, aerosols, black carbon deposition on snow and sea ice, and postfire changes in surface albedo.” They studied the large 1999 Donnelly Flats fire in central Alaska and found that in the first year after the fire, the emitted greenhouse gases, black carbon on snow and ice, and emission of aerosols increased the radiative forcing and in fact would have enhanced global warming. However, as the surface reflectivity increases many years after the fire, boreal fires ultimately will have a cooling effect. They state that “The net effect of all agents was to increase radiative forcing during the first year (34 ± 31 Watts per square meter of burned area), but to decrease radiative forcing when averaged over an 80-year fire cycle (−2.3 ± 2.2 Watts per square meter) because multidecadal increases in surface albedo had a larger impact than fire-emitted greenhouse gases.”

Another recent article published in The Holocene provides even more interesting information about fires in high latitude forests. A team of scientists from the University of New Hampshire and the University of Maine examined ice cores collected in the Yukon of Canada, and Yalcin et al. note that periods of high fire activity appear in the ice cores as zones with elevated ammonium cation (NH4+); they state that “forest fires may be the dominant source of NH4+ in the Arctic and Subarctic free troposphere during summer.” The basic approach is to measure the chemical structure of the cores and assume periods of high concentrations of NH4+ are associated with times of high wildfire activity. From the most recent 250 years, the results show that the “ice cores record high fire activity in the AD 1760s, 1780s, 1840s, 1860s, 1880s, 1890s, 1920s-1940s and 1980s.” They present the figure shown below (Figuire 1) for the last 1,000 years, and the figure indicates the greatest fire activity occurred from 1240-1410 AD and fire activity has declined since.

Figure 1. Forest fire activity in the Yukon and Alaska for the past 1,000 years. The dashed line indicates one standard deviation above the mean positive NH4+ residual (from Yalcin et al., 2006)

We are told by some scientists had high latitude fires will enhance global warming, but when Randerson et al. looked into it more carefully, they found just the opposite. Their results indicate that in the long run, wildfires in boreal areas may have a cooling effect. Global warmers tell us wildfires will increase, but when fires are reconstructed by Yalcin et al. for 1,000 years in the Yukon, we find that wildfires clearly have decreased.

Once again, we find that theoretical greenhouse predictions are not supported by evidence collected all over the planet. In the case of wildfires, many predictions simply go up in smoke when one examines the evidence.


Randerson, J.T., H. Liu, M.G. Flanner, S.D. Chambers, Y. Jin, P.G. Hess, G. Pfister, M.C. Mack, K.K. Treseder, L.R. Welp, F.S. Chapin, J.W. Harden, M.L. Goulden, E. Lyons, J.C. Neff, E.A.G. Schuur, and C.S. Zender, 2006. The impact of boreal forest fire on climate warming, Science, 314, 1130-1132.

Yalcin, K., C.P. Wake, K.J. Kreutz, and S.I. Whitlow, 2006. A 1000-yr record of forest fire activity from Eclipse Icefield, Yukon, Canada, The Holocene, 16, 200-209.

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