The recent spate of horrific and deadly wildfires in California has been accompanied by claims from proponents of catastrophic man-made warming of a link between climate change and increasing forest fires. There is wide acceptance among the media, “climate experts,” and the general populace that forest fires are increasing in frequency and size because of man-made climate change. As with drought, desertification, and heat waves, a link between warmer weather and more forest fires seems to be only common sense. Without deeper knowledge, one might logically surmise that warmer, and thus drier, weather means more fires.
The news media pumps up its ratings by broadcasting spectacular images of forest fires, particularly when they are fatal. Reporters regularly proffer opinions that man-made warming is to blame for the loss of life and property.
This is really a window into what global warming looks like. It looks like heat. It looks like dryness. It looks like this kind of disaster. — Dr. Michael Oppenheimer
Contrary to computer models that support the predictions of climate alarmists, real-world data indicate that “experts” like Dr. Oppenheimer are, in fact, incredibly wrong. The science and research of fire in the northern hemisphere is quite clear, there has been a significant decline in forest fires over the last 100-plus years and it is happening, not in spite of rising temperatures and increasing CO2, but because of it.
The scientific reasoning for declining fires is twofold, but both contribute to an increase in global soil moisture content, decreasing the forest fire potential. Firstly, the major cause of water loss in plants is attributable to the transpiration process in which plants take water out of the soil and expel it to the atmosphere. Due to the CO2 fertilization effect, increasing CO2 means that the plants’ stomata are open for shorter periods, the leaves lose less water and more moisture stays in the soil. Secondly, rising temperatures allow the atmosphere to increase the amount of water vapor it can carry, leading to additional rainfall and increased soil moisture.
This increased soil moisture has led to a “greening” of the Earth that is easily confirmed by recent NASA satellite data. According to Zhu (2016, Fig. 1) 25% to 50% of the planet over the last 35 years has seen an increase in vegetation while only 4% is “browning.”
A voluminous number of studies on the history of fire activity support the notion of a long-term decline of forest fires that began at the end of the Little Ice Age (circa 1850). The National Interagency Fire Center provides extensive information on forest fires in the United States (NIFC 2017, Fig. 2). The data show a declining number of fires over the last 30 years. This mere fact is certainly at odds with nearly everything we have heard to date on the subject.
One of the most extensive studies on the long-term fire trends was completed by a team of scientists with the Canadian Forest Service (Flannigan 1998). They compared temperatures and CO2 concentration versus frequency of forest fires over the last 150 years in North America and northern Europe. The authors stated “We believe that global warming since 1850 may have triggered decreases in fire frequency in some regions and future warming may even lead to further decreases in fire frequency." Their conclusion is powerful: “All empirical studies have shown either a decrease or no change in fire frequency during the 20th Century.”
Yet another landmark study in 2014 found that acreages burned worldwide in the 20th and early 21st centuries had declined significantly (Yang 2014 FIg. 3). The authors attributed the decline in high-latitude forest fires, particularly in most of North America and Europe, primarily to rising CO2 concentrations and their fertilization effect on plants and the resulting greening of the planet and a warmer climate that increases soil moisture.
The media and alarmist groups tell one story while the data tell quite another. Rather than an increase in the frequency and intensity of forest fires, as we have heard for many years, there are fewer forest fires, thanks to more CO2 in the air and more water vapor associated with increasing temperatures. This is a very inconvenient fact for the anti-fossil-fuel groups that ruthlessly exploit the tragedies of others to raise funds for their causes. In the future, it will be very difficult to appeal for money on the basis of forest fires when it becomes known that more CO2 and warmer temperatures mean fewer forest fires.
Flannigan MD, Bereron Y, Engelmark O, Wotton BM (1998) Future wildfire in circum-boreal forest in relation to global warming, Journal of Vegetation Science 9, pp 469–476
HadCRUT4 (2017) The Hadley Climate Research Unit (HadCRUT4) annual global mean surface temperature dataset, http://www.metoffice.gov.uk/hadobs/hadcrut4/data/current/download.html
NIFC (2017) National Interagency Fire Center - Total Wildland Fires and Acres (1960 – 2015), https://www.nifc.gov/fireInfo/fireInfo_stats_totalFires.html, accessed 04/2017 Tans P, Keeling R, (2017) Trends in Atmospheric Carbon Dioxide. Earth System Research Laboratory (ESRL), Global Monitoring Division, NOAA https://www.esrl.noaa.gov/gmd/ccgg/trends/data.html
Yang, J, Tian H, Tao B, Ren W, Kush J, Liu Y, and Wang Y (2014) Spatial and temporal patterns of global burned area in response to anthropogenic and environmental factors: Reconstructing global fire history for the 20th and early 21st centuries, J Geophys Res Biogeosci, 119, 249 263, doi:10.1002/2013JG002532.
Zhu Z, et al. (2016) Greening of the Earth and its drivers, Nature Climate Change 6, 791–795