USA — The huge wildfire scorching one of Americas most beloved national parks, Yosemite, has rained ash on San Franciscos water supply and jolted the nation.
Experts say this is just a foretaste of major fires to come, in the United States and much of the world.
Increasing incursions by humans into forests, coupled with altered forest ecology and climate change, will make fires bigger and more destructive, with implications for air quality as well as homes and infrastructure.
We face the increased risk of fires almost everywhere, said Chris Field, director of the department of global ecology at the Carnegie Institution for Science, who is co-chairman of a working group for the Intergovernmental Panel on Climate Change.
There have always been forest fires, of course. But their patterns are changing because of people.
Humans are often responsible for starting the fires, accidentally or intentionally; some spin out of control. The suppression of smaller fires can lead to buildups of burnable brush that can feed a huge, destructive blaze when it is sparked. That is true of the California blaze and many others in the American West; it is also what has happened in significant recent blazes in Turkey, according to Chadwick Oliver, director of the Global Institute of Sustainable Forestry at Yale University.
We dont need much of a spark to set off a fire that spreads long distances through the crowded, continuous forests, Dr. Oliver said.
And climate change, to which humans contribute, is heating up and drying out some though not all areas.
Global studies of wildfire patterns are rare. But a paper published last year in the journal Ecosphere predicted that climate change would have an effect on wildfires that varies widely, especially in accordance with a given regions precipitation patterns.
The paper which focused on climate change but not other variables, like changing land management projected that dry parts of the middle latitudes and Australia are likely to see more fires over the long term. The American West, already a tinderbox, will become more fire-prone. So, too, will high-latitude areas, the study found, partly because the carbon-rich peat soil there will burn under extreme weather conditions.
The pattern of increased wildfires by the end of this century appears clear for temperate and northern regions of the world, and it is most striking for the boreal forests/taiga and tundra biomes, the paper stated.
Parts of the tropics may become less fire-prone with climate change, the study said. That is because global climate models largely agree that areas near the Equator will see more precipitation with climate change, according to Max Moritz, one of the Ecosphere studys researchers, who heads a laboratory focused on fires at the University of California, Berkeley.
This would all other things being equal tend to dampen prospects for fire in the equatorial rain forests, Dr. Moritz said, adding that further research on seasonal precipitation patterns was needed.
Significant risks remain for the tropics, Dr. Field of the Carnegie Institution for Science noted. People sometimes set fires to clear land and the loss of some parts of a tropical forest to fire or clear-cutting can create a feedback effect.
One of the big concerns in Brazil, especially, is we know that the forests play a role in the amount that it rains, Dr. Field said. Moisture in the Amazon is recycled so if there is less forest to do the recycling, the rest becomes drier and more vulnerable, he said.
Next March, the working group of which Dr. Field is co-chairman at the Intergovernmental Panel on Climate Change, the U.N. group, will publish a report that discusses wildfires as part of a broader look at the effects of climate change and the vulnerabilities of certain areas.
When large fires burn, they can have serious international consequences. In a sense, Dr. Field said, they are a teachable moment, showing the risks of climate change.
Recent fires in Indonesia have grabbed headlines for causing air quality and haze problems throughout the region, in places including Singapore. That carries major health and economic concerns, said David Ganz, an official based in Bangkok with Lowering Emissions in Asias Forests, a program funded by the U.S. Agency for International Development.
It is such an important issue that the most widely known Association of Southeast Asian Nations agreement is on transboundary haze, said Dr. Ganz, who is also an author of the Ecosphere study.
In the Arctic regions, fires fueled by the carbon-rich peat might release a vast amount of greenhouse gas emissions.
These fires are happening more often in that region, Nick Sundt, a former firefighter who now directs climate communications for the World Wildlife Fund, said of the Arctic. Theyre bigger.
Those emissions hold true in parts of the tropics as well.
Indonesia and Malaysia have extensive peatlands that are extremely sensitive to fire, Dr. Ganz said. Once these peatlands are burned, enormous amounts of greenhouse gases will be released into the atmosphere, making the climate change issue worse over time.
He suggested that international climate agreements provide more incentives to developing countries in Southeast Asia so that people there reduce their use of fire to clear land.