June 14, 2010

Raining on Boreal Forest Fires

Filed under: Climate Changes, Precipitation

No presentation on global warming is complete without images of some major wildfire – from day one, the global warming alarmists have insisted that a warmer world will generate more wildfires thereby devastating ecosystems from sea to shining sea. It is an easy sell – higher temperatures will increase potential evapotranspiration, forests dry out, and therefore become far more susceptible to fire. Recall that the entire global warming issue became front-page news back in 1988, and 1988 was the summer Yellowstone Park and much of the western United States suffered severe forest fires. Ever since, every major fire somehow gets linked to global warming. We searched the internet for “Fires and Global Warming” and found literally thousands of websites claiming that global warming will cause more fires, fires are causing global warming, and of course, global warming leaders should be fired!

A recent article has appeared in Global Change Biology written by seven scientists with various institutions in Canada, France, and Germany that might come as a surprise to the alarmist camp. Girardin et al. begin their article noting “Recent extreme forest fire years across North America and Eurasia have raised awareness of potential human-caused effects on this disturbance agent. Notably, the activity of large fires increased strikingly in the mid-1980s in the western United States, northwestern Canada, and northeastern Quebec, and, at the end of the 20th century, in Russia. Human-caused climate change has often been viewed as a major contributor to this upward trend, among other factors.” No kidding – thousands of websites insist that fires are becoming more frequent and emissions of greenhouse gases are to blame.

Girardin et al. also note with respect to mid-to-high latitude boreal forests “climate change may act upon fuels through increased evapotranspiration not compensated for by increasing precipitation, or increased frequency of extreme drought years due to more persistent and frequent blocking high-pressure systems. Earlier snow melt and longer summer droughts with climate change could also expose forests to higher wildfire risk, although this effect remains to be validated.” Fair enough, but they seem to jump off the reservation as they state “Some contradictory evidence in the literature has led authors to question the likelihood of seeing an increase in boreal wildfire risk under warming of the Northern Hemisphere. Despite warming since about 1850 and increased incidence of large forest fires in the 1980s, a number of studies indicated a decrease in boreal fire activity in the last 150 years or so.” What? A decrease in boreal fire activity over the past 150 years?

The authors reinforce their claim that fires activity has decreased noting “The fact that diminishing fire activity has also been detected on lake islands on which fire suppression has never been conducted provides another argument in support of climate control.” These authors are not going to win any awards finding evidence that fire activity has decreased and the decrease is related to changes in climate. They must enrage the climate change alarmists writing “There is no consensus on the relative importance of climate change since the early 1900s on driving changes in wildfire risk in circumboreal forests. A primary reason is the lack of long-term, annually resolved fire statistics from unmanaged/undisturbed forests.”

The group focused their attention on the boreal forests of North America and Eurasia over the period 1901 to 2002 (see Figure 1 below). They analyzed a monthly time series of the July “monthly drought code” and determined that the MDC is very significantly related to the “annual area burned” (AAB).


Figure 1. Map of Northern Hemispheric boreal forests (from Girardin et al., 2009)

Don’t look now, but their results are not supportive of any claims that overall fire activity is on the rise. One quick glance of a key figure in the article (Figure 2) fails to show any large, widespread upward trend in fire activity. Instead, a varied pattern of change was observed. Girardin et al. state:

Our analyses did not reveal widespread patterns of linear increases in dryness through time as a response to rising Northern Hemisphere temperatures.

and explain,

Instead, we found heterogeneous patterns of drought severity changes that were inherent to the nonuniformly distributed impacts of climate change on Northern Hemispheres lands. Notably, significant trends toward increasing summer moisture in southern boreal Canada were detected. The diminishing wildfire risk in these regions is coherent with widely reported decreases in the area burned since about 1850, as reconstructed by dendrochronological dating of forest stands…Conversely, we found some evidence for increasing percentage of area affected by extreme droughts and occurrence rates of extreme drought years in northern taiga ecosystems (mostly over Eurasia).


Figure 2. Regional averages of the July monthly drought code (MDC, solid line) vs. logarithmic-transformed annual area burned (AAB, dashed line) in (a) the state of Alaska, (b) northwestern Canada, (c) the province of Ontario, (d) the province of Quebec, (e) the St. Petersburg region (European Russia), (f) the Komi Republic (European Russia), and (g) Russia. The square of the Spearman rank correlation (r2) expresses the goodness-of-fit between AAB and July MDC records over their common period (from Girardin et al., 2009).

As we have noted so many times before, had the team found evidence of a large widespread increase in forest fire activity, we would have seen global coverage everywhere with pictures of burning forests, ecosystem destruction, and of course, some cute wild animal looking at their burned-out home. Add some images of industrialization (particularly in the United States), make all the usual claims about global warming and fires, and people around the world would “get the message.” But Girardin et al. found no increase, so you had to come to World Climate Report for the skinny.

Reference:

Girardin, M.P., A.A. Ali, C. Carcaillet. M. Mudelsee, I. Drobyshev, C. Hély, and Y. Bergeron. 2009. “Heterogeneous response of circumboreal wildfire risk to climate change since the early 1900s. Global Change Biology, 15, 2751–2769.




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