Humans have raised CO₂ levels in the atmosphere to 50% above what they were before the industrial revolution. As a result, the world has already warmed by 1.1°C over the past century and reports indicate that it could reach 2.7°C of warming by the end of this century.
Bouts of severe drought, heat and low humidity are becoming more extreme as the climate warms. As climate change makes hot and dry conditions — often termed “fire weather” — more common and severe, vegetation dries out and landscapes become more flammable, pushing up the odds of dangerous wildfires.
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Scientists can measure changes in fire weather (temperature, humidity, rainfall and wind) to rate the level of danger of a wildfire striking. In a new global analysis, we found that, in many regions of the world, the pace at which fire weather conditions are increasing is accelerating faster than climate models predicted.
We used weather observations and climate models to assess historical and future trends in fire weather to find out how conditions are changing in specific countries and regions. We also analyzed data from other recent studies to assess how likely it is that future changes in fire weather will lead to more wildfires, based on relationships between fire and the climate, human use of the land and changes in plant growth.
We found that the length of the fire weather season (when most fires tend to occur) has already expanded significantly in many regions since the 1980s. On average, this season has lengthened by 27% globally, but the increases have been particularly pronounced in the Amazon, the Mediterranean and the western forests of North America.
Fire seasons are expanding. Asterisks signal the level of global warming at which extreme fire weather is unprecedented compared with the pre-industrial climate. CMIP refers to the group of climate models used.
Jones et al. (2022), Author provided
The number of days with extreme fire weather — when temperatures are particularly high, recent rainfall and humidity is particularly low and winds are capable of fanning a blaze — have become 54% more frequent at the global level. Because of this, larger and more severe fires that are difficult to contain are now more likely than they were in the past. This is one of the reasons that some of the recent fires in the western US or Australia have been so extensive and damaging. More extreme fires burn more vegetation, exacting a heavier toll on ecosystems and emitting more CO₂ to the atmosphere.
More days each year see extreme fire weather conditions in major fire-prone regions.
Jones et al. (2022), Author provided
We also predicted that climate change’s influence on fire weather will escalate in the future, with each additional degree of global warming substantially enhancing the risk of wildfires by preparing the landscape to burn.
If global temperatures reach upwards of 2°C above the pre-industrial average, fire weather conditions will be virtually unrecognizable compared with those in the recent history of most world regions.
Climate change is pushing wildfire risk into uncharted territory worldwide.
Jones et al. (2022), Author provided
People still influence wildfire occurrence
Climate change and its effect on fire weather, however, is not the only factor driving changes in wildfire activity. Human actions strongly affect the odds of risky weather conditions spawning a wildfire, either pushing with or pulling against the effect of climate change.
Fires caused by people are especially relevant outside of the vast northern forests of Eurasia and North America, where there are few dense population centers and many fires are set by lightning. Closer to towns and cities, sparks from faulty power lines or agricultural machinery, arson, or the use of fire to burn farming or logging residue, for example, increase the risk of wildfire.
But people have also inadvertently made large conflagrations less likely by making it harder for wildfires to spread through naturally fire-prone landscapes. This includes, for example, converting forest to farmland, or breaking up the highly flammable grassland vegetation of savannahs in Africa, Brazil and northern Australia.
The common approach of fighting fires in naturally fire-prone landscapes — applied in many regions of the US, Australia and Mediterranean Europe — can suppress blazes for a time, but these forests end up accumulating excessive vegetation fuel, which has contributed to more severe wildfires, especially during droughts.
Some ecosystems co-evolved with fire. Suppressing it can do more harm than good in the long run.
Kirsanov Valeriy Vladimirovich/Shutterstock
Although weather conditions conducive to wildfires are on an upward trajectory in nearly every part of the world, human actions still mediate or override the climatic influence in many regions. This may seem encouraging, but the effectiveness of human efforts to dampen the role of climate change diminishes with every additional decimal of a degree of warming.
Predicting how climate change and human activity will affect future wildfire risk worldwide is difficult, but one aspect is very clear. Slowing and reversing the accumulation of CO₂ and other greenhouse gases in the Earth’s atmosphere will slow the acceleration of wildfire risk. Weather conditions promoting fire have already increased faster than anticipated in many wildfire-prone regions, and committing to further warming through emissions will undoubtedly raise them further.
Failing to keep global warming under 2°C, the minimal goal of the Paris Agreement, carries a dangerous price: unprecedented wildfire risks on the world stage. What we do next matters.
Stefan H Doerr, Professor of Geography and Director of the Centre for Wildfire Research, Swansea University; Cristina Santín, Investigadora Ramón y Cajal, Instituto Mixto de Investigación en Biodiversidad (Universidad de Oviedo -CSIC); John Abatzoglou, Associate Professor of Engineering, University of California, Merced; Matthew William Jones, NERC Independent Research Fellow in Physical Geography, University of East Anglia, and Pep Canadell, Chief Research Scientist, Climate Science Centre, CSIRO Oceans and Atmosphere; Executive Director, Global Carbon Project, CSIRO
This article is republished from The Conversation under a Creative Commons license. Read the original article.
How wildfires have worsened in recent years
How wildfires have worsened in recent years
A series of lightning storms in mid-August 2020 hit Northern California, a region already experiencing a severe drought season, igniting what would become the August Complex fire. Over the course of almost three months, it burned through national forests, destroying 935 buildings and forcing the evacuation of thousands of people. By the time it was fully contained, its total range was over twice the size of California’s previous record and among the largest fires in U.S. history.
Less than a year later, the August Complex’s record was nearly broken when the Dixie fires broke out in Northern California, burning more than 963,000 acres and destroying more than 1,300 structures in the region.
Stacker cited data from the National Interagency Fire Center, National Oceanic and Atmospheric Administration, and the California Department of Forestry and Fire Protection to visualize how the spread of wildfires has worsened in recent years.
New breakouts of megafires (fires burning in excess of 100,000 acres) have become a seasonal repetition in the Western United States. Wildfires are innate to forest ecosystems, clearing out dead debris and paving the way for new growth, but climate change has elongated dry seasons, increased temperatures, and widened the potential for large-scale wildfires. Beyond weather-related factors, the prevalence of insects like bark beetles damage trees and make them more prone to burning. Invasive vegetation such as cheatgrass also easily burns and contributes to spread.
Trees, traditionally a storage vessel for carbon, release carbon immediately when burning and during decomposition. The EU’s Copernicus Atmosphere Monitoring Service estimated that global wildfires in 2021 released 1,760 megatonnes of carbon emissions, just over what the nation of Russia emitted in 2020. Black carbon, or soot, can also travel beyond wildfire zones, absorbing sunlight and warming the earth further.
Beyond the environmental threats, the widening reach of wildfires threatens the displacement of countless residents. The Marshall fire in January of this year destroyed more than 1,000 homes in Colorado, demonstrating the harm a wildfire can cause in a densely populated area such as the suburbs. The Camp Fire in 2018 permanently displaced an estimated 20,000 residents in California’s Butte County. Despite this, people continue moving to wildfire-prone areas, putting a growing population at risk of longer fire seasons and associated health risks.
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The number of wildfires is decreasing, but more acres are burning
Throughout the mid-20th century, forest management largely focused on preventing forest fires of all scales. Smokey the Bear was a national mascot for fire prevention, overseeing a multi-decade decrease in the number and average size of fires. But without regular fires, debris built up. This, combined with other environmental factors, eventually fueled costlier, large-scale blazes that have come to define the current wildfire season.
Despite having nearly 10,000 fewer fires per year on average from 2011-2021 compared to 1983-2010, the average acreage burned by those fires per year has more than doubled. From 1983-2010, the average number of acres burned per year was about 4.4 million. That number has jumped to 7.5 million acres per year for the 2011-2021 time period.
Wildfire seasons are getting longer
The total acres burned by wildfires in December 2020 was three times greater than the 10-year average for the month. The following year also experienced a damaging December, with a less extensive but still above average spread covering 336,984 acres. Wildfire season traditionally lasts May through October, but shorter winters and earlier snow melts have extended wildfire risk. 2021 set a record for days at preparedness level 5, the highest alert for wildfire risk.
The USDA Forest Service warned in 2021, “For years, agencies relied on seasonal firefighters for summer months, but now that wildfires are burning into the winter, they need to reevaluate their hiring plans.”
Wildfire suppression costs have risen by billions of dollars
With the increasing severity of wildfires every year, it follows that more resources are required to tame the blazes. In 1999, just before the turn of the century, the Forest Service and all other Department of the Interior agencies spent a combined $515.5 million on wildfire suppression. During the course of the last decade, the average cost of wildfire suppression has skyrocketed to nearly $2.1 billion annually. The Forest Service carries the brunt of this cost, contributing approximately three-quarters of the funds each year.
Though there is not currently an official tracking mechanism for the cost of wildfire damages, academics across the country have attempted to estimate the economic impact of wildfires. In 2020, a team of researchers estimated that the 2018 California wildfires caused $148.5 billion in economic damages.
Lightning fires are causing more damage in the West
At the national level, 89% of wildfires were caused by humans in 2021, but human-caused wildfires contributed only to 42% of total acreage burned. In the Southern and Eastern U.S., human-caused fires still cause the most damage, but elongated dry seasons in the West have intensified the impact of lightning when it does strike.
Dry lightning is created through high-altitude thunderstorms. Extreme heat and drought can cause rain to evaporate before it reaches the ground. Lightning fires can also pose greater damage because it can take longer for them to be detected, whereas human-caused fires are often closer to towns and high-traffic areas. Winds associated with dry thunderstorms can further fan the flames as well. These factors mean that even as the West is less prone to lightning than other parts of the country, the bolts can spark more damage.
California’s wildfires continue to set records
While lightning has sparked some of the most devastating fires in California including the August, SCU, and LNU complex fires, powerlines have also fueled far-reaching damage. Contact with overgrown trees, downed lines, and frayed wires can spark flames. Pacific Gas & Electric was held responsible for the 2018 Camp Fire and 2019 Kincade Fire and has instituted rolling blackouts on high-risk wildfire days.
Even as the origin of fires varies, each is exacerbated by existing environmental factors. A 2018 survey from the USDA Forest Service identified nearly 150 million trees that died between 2010-2018 in California. Two years later, 2020’s record season burned nearly 4.4 million acres and the five largest megafires happened concurrently in August and September. The season demonstrated how the buildup of vulnerable trees can ignite unprecedented spread.
A 2021 aerial survey by the USDA Forest Service offered some hope. Annual tree mortality has declined over the past five years, with an estimated 9.5 million dead trees in the state spanning more than 1 million acres, although tree mortality remains at a much higher rate than California’s pre-drought levels in the early-2000s.
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