A massive wildfire in California’s Yosemite National Park expanded to more than 2,300 acres over the weekend and into Tuesday, threatening some of the world’s oldest giant sequoia trees and forcing officials to evacuate more than 1,600 visitors from a nearby campground Monday. Some scientists worry the blaze signals that forests in the region may have reached a climate tipping point, with increasingly intense wildfires reinforcing deepening drought conditions in a dangerous feedback loop.
Ecologists have long considered giant sequoias, which can tower hundreds of feet above the ground and live for thousands of years, almost impervious to flames. The trees depend on the heat from blazes to release their seeds. And for thousands of years, fires have commonly passed through sequoia groves, burning brush and smaller trees, while leaving the much larger sequoias relatively unscathed.
But that has changed in the last decade, as drought, wildfires and insect infestation—all exacerbated by climate change—have contributed to the deaths of a surprisingly high number of giant sequoias in their native habitat along the western slope of California’s Sierra Nevada mountain range. In fact, in the last two years alone, increasingly severe wildfires have killed as many as one-fifth of the estimated 75,000 sequoias living in those groves, shocking forestry experts who say such deaths point to a grim milestone for the climate crisis. Slow fires that once stayed on the ground are now more frequently racing through the treetops as crown fires.
“I cannot overemphasize how mind-blowing this is for all of us,” Christy Brigham, chief of resources management and science at Sequoia and Kings Canyon national parks, told the Visalia Times-Delta in the wake of last year’s devastating Castle Fire. “These trees have lived for thousands of years. They’ve survived dozens of wildfires already.”
Many scientists, including those who helped compile the latest report from the United Nations’ Intergovernmental Panel on Climate Change, now warn that the impacts of global warming are accelerating far faster than previously believed and that old-growth forests like California’s sequoia groves are rapidly turning from vital carbon sinks into major sources of carbon emissions.
Last year, wildfires in the United States, Turkey and parts of Siberia emitted an estimated 1.76 billion tons of carbon dioxide into the atmosphere, the equivalent of more than a quarter of the annual carbon emissions of the U.S., according to scientists with the Copernicus Atmosphere Monitoring Service. And as rising greenhouse gas emissions push temperatures higher, it’s exacerbating the drought conditions that have helped fuel the West’s intense fires, which then release carbon dioxide, soot and other climate-warming pollutants into the atmosphere in a self-perpetuating cycle.
In some cases, the smoke wildfires spew into the air contributes to less annual precipitation. The largest and hottest fires can create their own weather, driving winds that fan the flames to burn hotter and spread wider, and even forming pyrocumulonimbus clouds that can drop lightning to start new fires or spawn fire tornadoes.
Those factors have made fire conditions so severe in recent years that they now threaten even the hardy sequoias, Nathan Stephenson, a scientist emeritus with the U.S. Geological Survey who specializes in the effects of global warming on forest ecosystems, told me in an interview.
“If you had asked me as recently as the middle of 2014, ‘Do you see the effects of a changing climate on giant sequoias?’ I would have said no,” Stephenson said. Now “with giant sequoias, it feels like a threshold has been reached and we’re seeing changes of the sort we haven’t seen before.”
Other forestry ecologists have echoed similar concerns, worrying that the rapidly accelerating impacts of climate change could soon make some of the nation’s most iconic landscapes and important ecosystems inaccessible for humans and uninhabitable for other species. National parks like Yosemite and Yellowstone are some of the country’s most treasured tourist destinations and provide critical habitat for many of America’s fauna and flora.
For decades, experts have called for adaptation plans to harden U.S. national parks against the effects of global warming, saying park officials need to move from a purely preservation role to one that takes more active management responsibilities, such as clearing away brush and other potential fuel for fires. But the development of such plans, especially at the federal level, has been slow, with the National Park Service releasing guidance to help park planners incorporate climate change into their decision-making only last year.
In fact, when heavy downpours last month sent record-shattering floods through Yellowstone National Park, tearing down trees and homes and even changing the courses of rivers, at least one former Park Service official called the situation the result of failed federal policy.
“When I heard they were evacuating every visitor from Yellowstone, I was like, ‘Oh my god, evacuating every visitor was not a part of our climate change scenarios,’” Marcy Rockman, a former climate change adaptation coordinator for the Park Service, told CNN. “Seeing what my former colleagues at Yellowstone are having to deal with now, it’s like … I’m worried for them.”
As firefighters continued their efforts on Tuesday to contain the blaze in Yosemite’s Mariposa Grove, officials say more than 500 sequoias, including the park’s iconic Grizzly Giant, are still at risk.
Stephenson, of the U.S. Geological Survey, said that while he doesn’t expect large swaths of sequoias to die, he is worried about the fires potentially killing off the older ones. “What concerns me is losing the big 2,000-year-old sequoias because they can’t be replaced for 2,000 years,” he said. “That’s what has captivated people globally. The huge millennial-age sequoias are what people marvel at, and we’ve lost 13 to 19 percent of those in just two summers.”
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1,540 square miles
That’s how much of Brazil’s Amazon Rainforest, one of the world’s most important carbon sinks, has been destroyed so far this year by logging and wildfires, marking an 11 percent increase from last year’s already record-high deforestation rate, according to the country’s National Institute for Space Research.