This is how we know climate change is making wildfires worse

17 September 2020

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USA – Coastal redwood forests are not normally wildfire hot spots, and especially not during the summer. They stay cool and retain humidity late into the season thanks to the cold Pacific Ocean, which normally produces a thick fog, called the marine layer, that bathes the coast in a cooling mist.

Which is why the fire last month that charred trees in Big Basin Redwoods, California’s oldest state park, was so unusual.

This year, rainfall is only about 50 percent of normal. Daytime high temperatures this summer were warmer than usual — but what really fueled the fire here, after lightning strikes started the blaze, were the temperatures after dark. Instead of nighttime cooling, which increases humidity and dampens flames, high pressure inland pushed the coastal redwood forests almost six degrees warmer than normal overnight in August. It didn’t cool down. Firefighters couldn’t catch a break.

President Trump would like to believe that forest management, not climate change, is the reason for the more destructive wildfires that have burned the West this summer. “It’ll start getting cooler, you just watch,” he said at a briefing in California on the fires on Monday. When a state official told him that science indicates the opposite, Trump pushed back: “Well, I don’t think science knows, actually.”

This is false. There is widespread agreement among fire scientists that climate change amplifies the effects of land management decisions, in California and elsewhere. Yes, decades of policies designed to keep fires from burning or spreading at all probably contribute to the large fires in California’s Sierra Nevada. But many other parts of the state — and the world — without such a history have seen record-breaking fire activity this year. The blazes choking the Pacific Northwest and sending smoke across North America are a scalding-hot sign that climate change is here.

Only nine months ago, Australia experienced its worst bush fire season in modern history, with more than 45 million acres burned, an event made 30 percent more likely by warming temperatures. Siberia saw a record heat wave this summer because of climate change, including a reading of over 100 degrees well north of the Arctic Circle, leading to extensive wildfires in boreal peatlands that emitted record levels of carbon. In the United States, the failure of the Southwest monsoon contributed to the warmest and driest August on record in western Colorado. These conditions fueled the Pine Gulch Fire, now the largest blaze in state history.

Two weeks ago in Oregon, the normally cool western slopes of the Cascade Mountains burst into flames, with multiple large fires, pushed by unusually hot and dry east winds, razing the small towns that line the river canyons. The Douglas fir forests there are filled with moss and ferns, moisture-loving plants that — like California’s coastal redwoods — aren’t exactly known as good tinder. They burn once every few hundred years, when drought conditions align with extreme meteorology. The last time much of this area was aflame was in the 1890s. Before that, it was the early 1600s. Climate change increases the frequency of such events.

Earlier this summer, Death Valley recorded a temperature of 130 degrees, the hottest on Earth in the modern era (the period with reliable record-keeping). Record heat in the past two weeks has fueled fires throughout California, including the Creek Fire near my home, which forced the National Guard to help evacuate more than 200 people from remote areas of the Sierra National Forest. On the same day the Creek Fire exploded, burning tens of thousands of acres in just hours, cities in Southern California only a few miles from the ocean breached 120 degrees. Meanwhile, the Bear Fire made rapid runs downhill toward the city of Oroville in Northern California, killing at least 15 people. Only three years ago, all of Oroville evacuated when overwhelming rainfall compromised the dam upstream, the tallest such structure in the United States. The two events would be ironic if they were not so tragic.

These types of meteorological extremes are exactly what global climate models projected would happen, and we are seeing the effects on wildfires. If this was only a matter of forest management, fire seasons would not be getting longer in the remote boreal forests of Alaska — where management is minimal and fire suppression has always been limited primarily to protecting the few cities and towns that dot an otherwise untamed, vast landscape. In 2019, however, Alaska saw fire danger ratings that were literally off the charts as 2.5 million acres burned, and fire season lasted a month longer than normal. This in a place where the season is usually only two months long. Because these kinds of blazes are ignited by lightning and burn relatively unimpeded across the wilderness, such trends can be caused only by climate change.

Climate change models predict that we will see meteorological extremes that produce catastrophic fires in unexpected places and outside of normal fire seasons. For instance, an exceptional drought produced a fatal wildfire in the Great Smoky Mountains of Tennessee in 2016, when blazes near Gatlinburg burned more than 10,000 acres and killed 14 people. In 2011, Texas received the lowest amount of rainfall since reliable records started in the late 19th century, a drought compounded by the hottest summer on record. When strong winds from an incoming tropical storm picked up in September, they fanned the Bastrop County Complex Fire, which killed two people and destroyed more than 1,600 homes, well outside Texas’s normal fire season. Neither of these blazes could be blamed on poor forest management.

California is undoubtedly a fire-prone state, where wildfires burned regularly for millennia before Europeans arrived. And a century of fire suppression has altered forests by increasing the density of trees per acre and allowing undergrowth to build up — all of which becomes fuel when a wildfire ignites. But there’s a reason that climate change is frequently called a “threat multiplier.” The drought California experienced from 2012 to 2016 was made worse by climate change; many trees that died are now burning. Across the state, satellite data shows that fires are raging with much greater intensity and releasing more energy; this is a function of very dry vegetation combusting more easily.

Forest management, particularly prescribed burning, can do much to reduce the risk of extreme wildfires. But management alone is not enough. Any place that has vegetation can burn, and without action on climate change, we could see destructive  fires in parts of the country that have not had them for decades: New York and New JerseyMinnesota and MichiganWisconsin and Maine. All had catastrophic wildfires in the past, and all it takes is a dry, hot wind at the right place and time.

What we see in California and the Pacific Northwest now will be only the beginning.

Twitter: @pyrogeog

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