Playing Climate Whack-a-Mole again, this time with a recent outbreak of claims that forest fires will be worse due to climate change. For example:
Over the past 30 years, human-caused climate change has nearly doubled the amount of forest area lost to wildfires in the western United States, a new study has found.
The result puts hard numbers to a growing hazard that experts say both Canada and the U.S. must prepare for as western forests across North America grow warmer and drier and increasingly spawn wildfires that cannot be contained.
The PNAS study referenced is: Impact of anthropogenic climate change on wildfire across western US forests
Abstract: Increased forest fire activity across the western United States in recent decades has contributed to widespread forest mortality, carbon emissions, periods of degraded air quality, and substantial fire suppression expenditures. Although numerous factors aided the recent rise in fire activity, observed warming and drying have significantly increased fire-season fuel aridity, fostering a more favorable fire environment across forested systems. We demonstrate that human-caused climate change caused over half of the documented increases in fuel aridity since the 1970s and doubled the cumulative forest fire area since 1984. This analysis suggests that anthropogenic climate change will continue to chronically enhance the potential for western US forest fire activity while fuels are not limiting.
It’s Not That Simple
As usual, the screaming headlines exaggerate a more complex and nuanced situation. From the study author:
“We see these big increases in fuel aridity across the Western forests” from 1984 to 2015, Dr. Abatzoglou tells the Monitor in a phone interview. “But what we find is about half, only half, not all of it, but about half of it, is attributable to the human-caused climate change.”
That means that other factors, like natural variability, have compounded with climate change to result in longer fire seasons, larger individual fires, and a ninefold increase in the area burnt over the past 30 years.
Another factor could be the amount of dry, unburned wood that has built up over decades of efforts to suppress wildfires, suggests Abatzoglou. So one solution going forward could be to allow controlled fires to burn off that tinder when conditions are wetter. “We do see a really strong coupling between climate change and forest fire in the Western United States,” he says, but “I think there may be ways to weaken that relationship” – by minimizing fuel for these massive wildfires.
Case Study: Fort McMurray
That PNAS analysis is built upon climate models. On the ground, specific events show more clearly how human and natural fac tors contribute to a forest fires, and it is not so obviously linked to rising CO2. Blair King writes about Fort McMurray at Huffington Post (here):
We Can’t Blame Climate Change For The Fort McMurray Fires
So what actually caused the fire to be so severe? Well it appears to be a combination of the effects of El Nino and historic forest management decisions. To explain: after the Slave Lake fire in 2011 the Alberta Government sought advice on the fire situation. The result was the Flat Top Complex Wildfire Review Committee Report which made a number of recommendations and concluded:
Before major wildfire suppression programs, boreal forests historically burned on an average cycle ranging from 50 to 200 years as a result of lightning and human-caused wildfires. Wildfire suppression has significantly reduced the area burned in Alberta’s boreal forests. However, due to reduced wildfire activity, forests of Alberta are aging, which ultimately changes ecosystems and is beginning to increase the risk of large and potentially costly catastrophic wildfires.
Essentially the report acknowledged that the trees surrounding Fort McMurray are hard-wired for fire and if they are not managed properly then these types of catastrophic fires will become more common. The warm weather may have accelerated the fires season, but the stage was set for such a fire and not enough work was done to avoid it.
The Haines Index
No matter how a fire ignites, a forest fire becomes dangerous because of the weather conditions allowing it to start and to grow. The potential for forest fires is often indicated by the Haines Index (HI) that has been widely used for operational fire-weather forecasts in regions of the United States, Canada, and Australia. Several studies have shown a positive correlation between HI and observed fire activity.
An important study (here) demonstrates HI is strongly linked to ocean oscillation events such as El Nino.
The Interannual Variability of the Haines Index over North America
The Haines index (HI) is a fire-weather index that is widely used as an indicator of the potential for dry, lowstatic-stability air in the lower atmosphere to contribute to erratic fire behavior or large fire growth. This study examines the interannual variability of HI over North America and its relationship to indicators of large-scale circulation anomalies. The results show that the first three HI empirical orthogonal function modes are related respectively to El Nino–Southern Oscillation (ENSO), the Arctic Oscillation (AO), and the interdecadal sea ~ surface temperature variation over the tropical Pacific Ocean. During the negative ENSO phase, an anomalous ridge (trough) is evident over the western (eastern) United States, with warm/dry weather and more days with high HI values in the western and southeastern United States. During the negative phase of the AO, an anomalous trough is found over the western United States, with wet/cool weather and fewer days with high HI, while an anomalous ridge occurs over the southern United States–northern Mexico, with an increase in the number of days with high HI. After the early 1990s, the subtropical high over the eastern Pacific Ocean and the Bermuda high were strengthened by a wave train that was excited over the tropical western Pacific Ocean and resulted in warm/dry conditions over the southwestern United States and western Mexico and wet weather in the southeastern United States. The above conditions are reversed during the positive phase of ENSO and AO and before the early 1990s.
Forests Benefit from More CO2 and Milder Temperatures
A previous post (here) provided links to studies showing how US and other forests have generally become more healthy and resilient over recent decades. For example:
There is strong evidence from the United States and globally that forest growth has been increasing over recent decades to the past 100+ years. Future prospects for forests are not clear because different models produce divergent forecasts. However, forest growth models that incorporate more realistic physiological responses to rising CO2 are more likely to show future enhanced growth. Overall, our review suggests that United States forest health has improved over recent decades and is not likely to be impaired in at least the next few decades.
As well, the outlook for timber production is optimistic (here):
Although models suggest that global timber productivity will likely increase with climate change, regional production will exhibit large variability, as illustrated in Table 1. In boreal regions natural forests would migrate to the higher latitudes. Countries affected would likely include Russia and Canada. Warming could be accompanied by increased forest management in northern parts of some of these countries, particularly the Nordic countries, as increased tree growth rates are experienced. Climate change will also substantially impact other services, such as seed availability, nuts, berries, hunting, resins, and plants used in pharmaceutical and botanical medicine and the cosmetics industry, and these impacts will also be highly diverse and regionalized.
Another factor to consider is the effects of impacts other than climate change such as land-use change and tree plantation establishment. In many regions, these effects may be more important than the direct impact of climate. Indeed, over the past half-century industrial wood production has been increasingly shifting from native forests to planted forests. (my bold)
Again we see jumping to a conclusion to get a simple (simplistic) reduction of a complex reality. In legal terms, blaming forest fires on CO2 is a rush to judgment. Yes, forests are affected by more CO2 and milder temperatures. They grow stronger and more resilient to all kinds of threats, including forest fires. The incidence of forest fires is associated strongly with drier conditions resulting from ocean oscillations and accompanying atmospheric circulations. Humans play a role in land usage, timber management and fire suppression policies.
See link for more on playing Climate Whack-a-mole
I am proud of making a post title composed entirely of F-words. Apologies for any problems caused to stutterers. Old joke about the fate of a stutterer during an Air Force parachute training exercise. All the chutes of the trainees opened, except for one man who kept falling past the others. He was overheard saying: “Th-th-th-th-thr-three, Fa-fa-fa-fa-fou-four, Fi-fi- . . .”