The US wildfire season used to last about four months, beginning in late summer or early autumn. These days, it stretches six to eight months, according to the US Forest Service, and in some places it’s now a year-round affair.
In just five years, from 2018 through 2022, wildfires scorched 38.3 million acres across the country. That’s nearly 60,000 square miles, slightly bigger than the state of Georgia. Last year alone, nearly 69,000 wildfires burned 7.6 million acres, more than 40% of which were in Alaska.
Not only is the fire season longer, wildfires are burning larger areas more severely and at higher elevations. The average acreage that has burned every year since 2000 — 7 million — is more than double the annual average of 3.3 million acres in the 1990s, even though the annual average of 70,025 wildfires a year since 2000 is 12% less than in the 1990s.
There are a number of reasons why there has been so much more wildfire destruction this century, particularly in the western United States and Canadian southwest. Encroaching development in fire-prone areas and widespread fire suppression are among them. But another major culprit is climate change, which has intensified the heat and drought that have always been factors in western North America.
That climate change obviously didn’t just happen on its own. It mainly comes from burning fossil fuels, and a new Union of Concerned Scientists (UCS) peer-reviewed study — published on May 16 by Environmental Research Letters — calculates just how much of the acreage burned in forest fires in the western United States and southwestern Canada can be attributed to the carbon emissions from the world’s largest fossil fuel companies and cement manufacturers and their products.
The new report is the latest in a series based on a 2014 peer-reviewed study by Richard Heede, director of the Climate Accountability Institute, which identified 90 companies — 83 fossil fuel producers and seven cement manufacturers — that were responsible for nearly two-thirds of all industrial carbon dioxide and methane emissions between 1854 and 2010. Just seven private and state-owned companies — BP, Chevron, ExxonMobil, Gazprom, the National Iranian Oil Company, Saudi Aramco, and Shell — accounted for a whopping 18.7% of total emissions.
Since that 2014 study, which laid the foundation of what is called climate source attribution science, UCS scientists have collaborated with Heede on two other studies that pinpointed the major carbon producers’ culpability for specific climate change-related trends.
In 2017, UCS climate scientist Brenda Ekwurzel led a study that found that the 90 companies’ emissions contributed roughly 57% of the increase in atmospheric carbon dioxide, as much as half of the jump in global mean surface temperature (the average of the sea surface temperature and the air temperature over land), and as much as a third of global sea level rise since the mid-1850s. Ekwurzel was joined by Heede, then-UCS climate scientist Peter Frumhoff, and four other scientists.
Two years later, UCS climate scientist Rachel Licker conducted a study with Ekwurzel, Frumhoff, Heede, and two other scientists to determine the major carbon producers’ contribution to ocean acidification, caused when oceans absorb increasingly more carbon dioxide from the atmosphere, disrupting an ocean environment that had been relatively stable for tens of millions of years. Licker et al. found that the companies — down to 88 due to mergers — were responsible for about 55% of ocean acidification between 1880 and 2015.
The new study, focusing on the 88 carbon producers’ role in western North American wildfires, was conducted by six UCS Climate and Energy Program staff members and University of California Merced climatologist John Abatzoglou. The UCS scientists included Kristina Dahl — who led the study — Licker, Delta Merner, Pablo Ortiz, and Carly Phillips. They found that 48% of the increase in the region’s fire-friendly conditions since 1901 — specifically drier land and vegetation — can be traced to the 88 companies’ carbon emissions. They also calculated that the companies’ emissions have been responsible for 37% of the burned forest area in the region since 1986.
Dahl, Ortiz, and Phillips — along with their colleagues Alicia Race and Shana Udvardy — also published a brief report based on the Environmental Research Letters study. Titled The Fossil Fuels Behind Forest Fires, it provides a concise overview of the peer-reviewed study and makes policy recommendations for the Biden administration and Congress.
Just before the Environmental Research Letters study came out, I had a chance to ask Phillips some questions to provide more context. Phillips, who has a doctorate degree in ecology from the University of Georgia, was a Kendall fellow at UCS from 2018 to 2020 and then a researcher at the University of Victoria in British Columbia. She rejoined UCS earlier this year as a member of the Science Hub for Climate Litigation, just in time to contribute to the study.
EN: Welcome back to UCS. Why don’t you start by explaining why it is so important for scientists to figure out the role these companies and their products have played in creating the climate crisis.
CP: Major fossil fuel companies and their trade groups knew that burning fossil fuels would dramatically reshape our climate since at least the 1960s. In the 1970s and ’80s, Exxon’s own scientists predicted — with startling accuracy — how global temperatures would increase, as well as the consequences for humanity. Despite having this knowledge and the opportunity to change course to avoid catastrophic warming, fossil fuel companies took a page from the tobacco industry’s playbook and orchestrated a decades-long campaign to deceive the public, cast doubt on climate science, and delay climate action at all levels. But just like Big Tobacco in the 1990s, the fossil fuel industry must be held accountable for the damage it has caused. Dozens of cities, counties, and states across the country have filed lawsuits to do just that.
At UCS, our Science Hub for Climate Litigation supports a broad range of climate accountability lawsuits by fostering litigation-relevant research, connecting litigators to the scientists and scientific research that can best inform their cases, and providing training for scientists to engage with the legal system. Studies such as our new one, which directly link climate change impacts to the industry’s emissions, provide a critical piece of the accountability puzzle and may help to inform existing and future cases.
EN: OK. But how was Richard Heede able to calculate that, at the time, 90 companies were responsible for nearly two-thirds of the carbon emissions between 1854 and 2010? What went into that calculation?
CP: Great question. These 90 entities, now 88 due to mergers, are oil and gas producers, coal companies, and cement manufacturers. Rick Heede combined publicly available records about extracting and producing carbon-intensive materials with scientific data about the amount of carbon dioxide and other heat-trapping gases released into the atmosphere from manufacturing and burning each of these products. His calculations account for emissions from such processes as venting as well as the fact that creating some products, such as steel, can actually store some carbon. As a result, he was able to nail down the magnitude of what has been going into the atmosphere and its origin.
EN: You and your colleagues point out that the increase in burned acreage across the western United States and southwestern Canada over the last few decades is partly due to a rise in what’s called the “vapor pressure deficit.” It’s a bit counterintuitive. Climate change heats up the air, which then can hold more moisture, but the fact that the air can hold more moisture dries out soil and vegetation, making them more flammable.
CP: Right. Vapor pressure deficit (VPD) is not super-intuitive. It measures the difference between the amount of moisture in the air and the amount of moisture air could hold if it were totally saturated. The relationship between VPD and wildfire can be explained by three key concepts. One you already mentioned: Warmer air can hold more moisture. Another is “diffusion,” when molecules move from areas of high concentration to areas of lower concentration, similar to how food coloring disperses through a glass of water. And the third is “gas exchange.” When plants open their pores to exchange oxygen for carbon dioxide during photosynthesis, they lose water to the atmosphere because the concentration of moisture in a leaf is usually greater than that of the surrounding air. When VPD is high, meaning the air could hold a lot more moisture, water moves more quickly from the plant to the atmosphere, which ultimately dries out the plant.
EN: The Fossil Fuels Behind Forest Fires report briefly mentions the fact that wildfires threaten the health and well-being of the folks who live in the region. Wildfires obviously can destroy homes and businesses, but even when fire engulfs unpopulated land, wildfire smoke can have a profound impact on public health miles away.
CP: Exactly. Wildfire smoke is extremely dangerous and particularly harmful for vulnerable populations, including seniors, children, low-income community residents, and outdoor workers. A day of exposure to intense wildfire smoke is roughly equivalent to smoking seven cigarettes.
The smoke is full of tiny particulates that can pass through the lungs and into the bloodstream, which can lead to a higher incidence of asthma, heart disease, and premature death from such respiratory diseases as COVID-19. For pregnant people, smoke exposure increases the risk of pre-term birth.
Public health experts say that there’s no safe amount of exposure to wildfire smoke. For people who work outdoors, that can pose a huge challenge. They may have to choose between protecting their health and protecting their livelihood. Staying inside, meanwhile, is not necessarily much safer. Smoke has a way of getting into homes and businesses, so it is very difficult to avoid. Some people can afford an air purifier, but people who can’t have to breathe smoke-filled air. And, like you said, the impact may be most acute in the area surrounding a fire, but the full effect is definitely global. Wildfire smoke from the West Coast in 2020 degraded air quality in your hometown of Washington, D.C., and in cities as far away as Western Europe. Particulates from Western wildfire smoke have even been recorded on Greenland ice sheets.
EN: The Fossil Fuels Behind Forest Fires report offers recommendations for the Biden administration and Congress to hold carbon producers accountable. What should they do? What are your top recommendations?
CP: There are lots of things that the federal government could do to hold corporations accountable. For starters, the Securities and Exchange Commission should finalize, implement, and enforce strong rules mandating standardized corporate climate disclosure. These rules would require companies to report carbon emissions from not just their operations, but also from the use of their products. Second, Congress and the Justice Department should investigate the fossil fuel industry’s ongoing climate disinformation campaigns like the House Oversight Committee began to do last Congress, so that the general public can better understand exactly how the industry deceived everyone. Third, communities and litigators should pursue legal routes to hold fossil fuel polluters accountable for their disinformation campaigns and their scientifically proven contributions to climate damage. Just last month, the US Supreme Court cleared the way for cases filed in California, Delaware, Hawai’i, Maryland, New Jersey, and Rhode Island to move forward in state courts after more than five years of the fossil fuel industry defendants’ procedural delay tactics.
EN: Last January, the US Department of Agriculture announced that $490 million from the Inflation Reduction Act (IRA) will be dedicated to projects to reduce fire risks in seven western states. That funding is on top of the $440 million the Bipartisan Infrastructure Law earmarked for wildfire mitigation efforts. What’s your take on those efforts, and what else should the administration, Congress and state governments do to prevent wildfires?
CP: Given how western forests evolved alongside fire, wildfires will never be fully preventable — nor should they be. But we can do a lot to reduce the risks to communities.
The funding in the IRA and infrastructure law is a critical first step to reduce the risk of catastrophic fire in some areas of the US west by employing a range of strategies like removing vegetation, thinning dense stands of trees, and conducting prescribed burns, which is when a fire is deliberately set under specific weather conditions to manage a forest. But it’s important to stress that these initiatives are just a first step. Reducing the incidence and risk of devastating wildfires and learning to coexist with fire will require a yearly and multigenerational commitment to forest management.
Beyond the IRA and infrastructure law projects, federal agencies could promote improvements in at-risk areas by, among other things, establishing “defensible space” around property and requiring developers to use fire-proof and fire-resistant building materials. They also should prioritize these kinds of efforts in the highest-risk, lowest-resourced communities.
Congress, meanwhile, could provide and maintain funding for at-risk forests and scale up risk-reduction treatments, including forest thinning followed by prescribed burning. Congress can also remove obstacles to Indigenous-led land management, especially cultural burning, which has shaped western forests for millennia.
Beyond these forest-centric strategies, Congress should pass legislation to rapidly reduce heat-trapping emissions and ensure an equitable and just future. But that should go without saying.
By Elliott Negin, Union of Concerned Scientists’ The Equation
PART OF A SERIES ON Ask A Scientist
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