Report: Wildfire risks around the world likely to change dramatically

After crunching the numbers, the team found that for the period 2010 to 2039, model runs most consistently pointed to an increase in fire risk for biomes already in regions with warm climates. A handful of biomes in the tropics and subtropics showed small decreases in fire risks. But for this period fewer than half of the models agreed on the direction of change across the 14 biomes.

The team notes that this points to major uncertainties in the results. But it also falls in line with a feature of global warming many scientists have highlighted – its effects become more pronounced toward the latter half of the century than they are today. For many of the more-localized effects of climate change – from severe storms to heat waves to wildfire patterns – the climate's natural variability can still make it hard to tease out global warming's fingerprints.

But the team's model runs also indicate significant increases and decreases in risk during the final 30 years of the century. Fire risks increase for up to 62 percent of biomes in mid and high altitudes, while the risk drops by 20 percent, largely in the tropics. And the models are in much greater agreement.

During the 2010 to 2039 period, for instance, boreal forests, which cover a broad swath of Canada and northern Russia, stood about an equal chance of seeing increases or decreases in wildfire risk over relatively small expanses of the territory they cover. Most of the model results, however, in effect shrugged their digital shoulders.

During the 2070 to 2099 period, however, the vast majority of models agree that boreal forests will see an increased risk of wildfire over nearly all of its extent. The likelihood of increased risk runs from 66.7 percent for most of the boreal zone to 90 percent for a small but still significant fraction.

The results held a couple of surprises for the team, Moritz says.

"One is that in the near-term future, despite the fact that the global climate models have huge variations amongst them, about half the planet shows model agreement for disruptions" in fire regimes, he says. Those disruptions include decreases as well as increases in risk.

"As we crank the models forward, we saw much stronger agreement" and the patterns of increased and decreased risk, as well as consistency among models, solidifies, he says.

The other is projected decreases in fire risk for much of the tropics during the latter half of the century. "It's pretty striking," he says.

One potentially important drawback to the team’s approach – it doesn't capture year-to-year climate variability or features such as the El Nino-La Nina cycle – which plays a role in fire risks in some tropical rain forests.

Indeed, in most regions of the world, "fires are determined by more-nuanced aspects of climate variability, the sorts of climate and weather conditions that vary from between years or seasons," writes Cathy Whitlock, a researcher who focuses on climate and wildfire response at Montana State University in Bozeman.

Mortiz acknowledges the point, but adds that at this stage, global climate models do a poor job reproducing the cycles. The approach the team took – basing its analysis on a pair of 30-year intervals and the climate "normals" each would represent – smooths out those year-to-year changes.

Still, he says, if one could include such patterns, a future direction for the work, the results for the tropics might be different.

Another feature the approach lacks at this stage is the ability to feed in changes global warming could bring to the amount of landscape each of the 14 biomes covers as time progresses.

Despite the approach's limitations, it provides "insight into the complex fire responses that lie ahead, especially in the near term," says Dr. Whitlock.

And while the results don't attempt to predict changes to the expanse and distribution of the 14 biomes included in the study, the results could be set beside those of models that do predict those biome shifts to get a sense for the shift in fire risks those altered landscapes could face, she agrees.

IN PICTURES: Colorado wildfires

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