Changes in ignition, fire size, and burned area between 1975 and 2015. a,b, Increasing trends in ignition density between 1975 and 2015 in the Northwest Territories (a) and interior Alaska (b). c,d, There were no significant changes in fire size. e,f, In Interior Alaska there was an increasing trend in ann…. Graphic: Veraverbeke, et al., 2017 / Nature Climate Change

By Scott Waldman
27 June 2017

(Climatewire) – Climate change is driving up the number of forest fires ignited by lightning, and it's pushing them farther north, to the edges of the Arctic tundra, researchers say.

Lightning-caused fires have risen 2 to 5 percent a year for the last four decades, according to a paper published yesterday in the journal Nature Climate Change. And as thunderstorms intensify and become more frequent, fires are increasingly occurring in the boreal forests, and even on the permafrost tundra. Warmer temperatures encourage more thunderstorms, which in turn bring more lightning and greater fire risk.

The changes are part of a complex climate feedback loop that is only now becoming more clear to scientists, said Sander Veraverbeke of Vrije Universiteit Amsterdam, the study's lead author. A feedback loop is a series of interrelated phenomena that is worsened by climate change and continues to build upon itself with additional consequences. In the north, fires release more carbon dioxide and methane from the permafrost, he said.

"You have more fires; they creep farther north; they burn in these soils which have a lot of C02 and methane that can be exposed directly at the moment of the fire and then decades after," Veraverbeke said. "That contributes again to global warming; you have again more fire."

Scientists studied a spike in fires caused by lightning strikes in the Canadian Northwest Territories in 2014 and in Alaska in 2015. Because there is so little human activity in both of those regions, researchers traced the fires in remote areas to lightning strikes. [more]

Fires rise in Arctic as 'lightning follows the warming'

ABSTRACT: Changes in climate and fire regimes are transforming the boreal forest, the world’s largest biome. Boreal North America recently experienced two years with large burned area: 2014 in the Northwest Territories and 2015 in Alaska. Here we use climate, lightning, fire and vegetation data sets to assess the mechanisms contributing to large fire years. We find that lightning ignitions have increased since 1975, and that the 2014 and 2015 events coincided with a record number of lightning ignitions and exceptionally high levels of burning near the northern treeline. Lightning ignition explained more than 55% of the interannual variability in burned area, and was correlated with temperature and precipitation, which are projected to increase by mid-century. The analysis shows that lightning drives interannual and long-term ignition and burned area dynamics in boreal North America, and implies future ignition increases may increase carbon loss while accelerating the northward expansion of boreal forest.

Lightning as a major driver of recent large fire years in North American boreal forests



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