As Earth's climate warms up, Yellowstone National Park and the Grand Tetons are likely to experience large fires more frequently, according to a new study. Within just a few decades, big fires may become as much as 10 times more common than they have been in the last 10,000 years.
A bump in fire frequency would reverberate through the environment in unpredictable ways -- affecting the kinds of plants that grow in the area, the kinds of animals that can find habitats there and the amount of carbon that vegetation might be expected to pull out of the atmosphere.
Such a fiery future would also threaten people and homes throughout the northern Rockies.
"What surprised us is how early the changes become so extreme," said Anthony Westerling, a fire climatologist at the University of California-Merced. "By mid-century, the climate conditions combined with fire frequency are going to be incompatible with the kinds of forests that grow there now. There is going to be a transformation of the landscape. It's going to look really different."
Over the last few decades, the northern Rockies have experienced a relatively large increase in the frequency of fires, according to previous research by Westerling and colleagues, despite attempts to suppress and manage burns.
In years with warmer-than-average springs and summers, fires happen more often. And a mere half-degree Celsius temperature rise makes the difference between a high-fire year and low-fire year, Westerling said. Yet by 2099, conservative climate models predict that average temperatures in the Yellowstone region will rise by about five degrees C.
To investigate how warming might affect fire frequency in the area, the researchers started with those same conservative climate models, which simply assume humankind will continue to produce greenhouse gas emissions at the same rate we do now. After comparing climate conditions with fire frequency over the last few decades, they looked at predicted future changes to temperatures, moisture and precipitation levels. That helped them estimate what the availability of dry wood and the rate of fires will be like through the end of the century.
Over the past 10,000 years, severe fires have swept through the notoriously pristine Yellowstone area once every 100 to 300 years, usually as a result of lightning strikes. But by the end of the century, the researchers report today in the journal Proceedings of the National Academy of Sciences, big fires are likely to occur once every 20 to 30 years.
Fire is a normal part of nature, and many species depend on it. But such a drastic increase in fire frequency is bound to have profound, unpredictable effects on ecosystems in the region.
This study helps explain what people who live in the West have begun to notice in recent years, said Terry Chapin, an ecosystem ecologist who studies the effects of climate change on wildfires at the University of Alaska, Fairbanks. Serious wildfires seem to be happening more often than they used to, he said.
"This points out very clearly that these occasional bad fire years in the western United States that have caused incredible amounts of property damage and deaths are not an anomaly or the result of poor decisions on the part of fire managers," Chapin said. "Changes in climate are going to be more and more extreme, and trusting fire managers to get it right is not really addressing the core of the problem."
In other words, wildfires are soon going to become the norm through the mountainous west and possibly other regions. And there's not a whole lot that people will be able to do about it, except change where they choose to live and build homes.
"That's something the United States has not come to grips with, with respect to climate change: We assume that either climate change doesn't happen or that we can manage things such that climate change won't affect us," Chapin said. "This seems like a clear and present example where recent and projected changes in climate are going to have a huge impact on human society. We need to adjust and adapt rather than try to fix the symptoms."