Millions of acres scorched by wildfires in the Western US and Canada — an area roughly the size of South Carolina — can be traced back to carbon pollution from the world's largest fossil fuel and cement companies, scientists reported Tuesday.

The study by the Union of Concerned Scientists, published in the journal Environmental Research Letters, found that 37% of the area burned by wildfires in the West since 1986 — nearly 19.8 million acres out of 53 million — can be blamed on the planet-cooking pollution from 88 of the world's major fossil fuel producers and cement manufacturers, the latter of which have been shown to produce around 7% of all carbon dioxide emissions.

The amalgam of megadrought and record-breaking heat that's drying out vegetation due to climate change has stoked the West's wildfires. And researchers found that since 1901, and the fossil fuel activities of these companies, including ExxonMobil and BP, among others, warmed the planet by 0.5 degrees Celsius — nearly half of the global increase during that period.

Carly Phillips, a research scientist with the Science Hub for Climate Litigation at the Union of Concerned Scientists and co-author on the study, said the findings add to a significant library of research that directly links climate change or the impacts of the crisis to burning fossil fuel.

"We know that many of these companies have known for decades about the consequences of climate change," Phillips told CNN, referring to several studies and award-winning reports that have shown fossil fuel executives knew of but downplayed the growing threat. "But instead of sharing that information with the public, they engaged in this deliberate misinformation campaign to deceive the general public and cast doubt on climate science."

Fossil fuel companies have denied the conclusions of those reports.

"The clear agenda of this group aside, America's oil and natural gas industry is focused on delivering affordable, reliable energy while reducing emissions," Christina Noel, a spokesperson for the American Petroleum Institute, which represents the oil and gas industry in the US, told CNN in an email.

BP and Exxon have announced goals to achieve net-zero emissions in its operations by 2050. CNN reached out to BP and ExxonMobil about Tuesday's study, but did not hear back in time for publication.

The study comes as firefighters in Alberta, Canada, fight dozens of wildfires in the forest protection area of the province — fires that are being exacerbated by a dangerous heat wave with record-breaking temperatures in Western Canada and the US Pacific Northwest.

Researchers behind the study came to their conclusions using a method that scientists have relied on in recent years to quantify how much of a role the climate crisis is playing in extreme weather and environmental disasters: They took actual climate data and compare it to an idealized, modeled version of the world where there was no fossil fuel pollution from the 88 companies.

One metric they focused on was the region's so-called vapor pressure deficit — or how thirsty the atmosphere is for moisture. It is a key indicator of fire danger and drought, Phillips said, and measures how much the air is sucking moisture out of soil and plants, which then ultimately become fuel for wildfires.

The methodology is "simple," said Caroline Juang, researcher with the Lamont-Doherty Earth Observatory at Columbia University.

"The study takes what we know about the strong relationship between climate and burned area, and extends this understanding to the role of big fossil fuel emitters," Juang, who is not involved with the study, told CNN. "The authors use how global mean temperatures scales with [vapor pressure deficit] and then looks at how changes in [vapor pressure deficit] will change burned areas."

The researchers also accounted for aerosol pollution, which unlike planet-warming gases like carbon dioxide or methane, reflects sunlight back to space and has a cooling effect. Major oil and gas companies contribute roughly two-thirds of total industrial aerosol emissions, according to the study, which used fossil fuel emissions data through 2015, the latest available, and held figures constant from 2015 to 2021.

Jatan Buch, a postdoctoral research scientist in the Lamont-Doherty Earth Observatory at Columbia University, who was also not involved with the study, said that while vapor pressure deficit is the leading driver of year-to-year variability in burned area across the region, other factors play a role and should be examined in future studies. According to the study, those include precipitation and snowpack conditions and prescribed burns and fire suppression efforts that have led to a buildup of vegetation that help fuel fires.

The report also noted that development and growth contributed to a higher risk of human behavior-caused fires, with more people and property in harm's way.

In recent years, fires have exhibited increasingly explosive behavior — leading to larger burned areas, more aggressive nighttime fires and even massive fire-induced tornadoes like in the Carr Fire in California in 2018. The largest fires are also pouring smoke into the atmosphere, which can be transported large distances, impacting millions with poor air quality potentially hundreds of miles away.

"Even if you're not living near the fire, you can still feel those impacts," Phillips said. "What public health experts share is that there's no amount of exposure to wildfire smoke that's safe."

Climate scientists have said human-caused climate change plays a key role in making these extreme fire events worse and more likely to happen. Jennifer Marlon, a research scientist at the Yale School of the Environment, said that's why this study is so important.

"It shows how quickly the science about climate change causes is moving and gives us vital information about the very real harms to people from pollution from burning coal, oil and gas," Marlon, who is not involved with the study, told CNN.

"The failure of fossil fuel companies to abate their emissions after recognizing the climate risk of their activities in the mid-1960s is even more reprehensible," Buch told CNN. "The continued greenhouse gas emissions due to these companies' products in the late 20th century resulted in loading the dice for the western US climate toward a hotter and drier future with a higher likelihood of catastrophic wildfires."

Phillips said the key message they want people to take away from this study is that fossil fuel companies need to be held accountable for exacerbating extreme climate events like wildfires, which are putting lives at risk.

"It didn't have to be this way," she said. They "should pay their fair share of the costs of these climate impacts."