PARIS, Nov. 12 – Deadly fires, such as those raging in northern and southern California, have become more frequent in the state and the world in recent years. AFP has talked with scientists about the way climate change can make them worse.
Other factors have also encouraged the increase in the frequency and intensity of large-scale fires, including human intervention in forested areas and questionable forest management. "The patient was already ill," said David Bovman, professor of environmental biology at the University of Tasmania and a fire expert.
"But climate change is accelerating."
Good weather for the fire
Each firefighter can tell you the recipe for "good weather": hot, dry and windy.
It is not surprising that many tropical and temperate regions are devastated by the rise of forest fires that are predicted in climate models to see higher temperatures and more drought.
"In addition to bringing even more dry and hot air, climate change – increasing evaporation rates and drought prevalence – also create more flammable ecosystems," said Christopher Villiams, Ecology Research Director at Clark University in Massachusetts.
In the last 20 years, California and southern Europe have seen several droughts of size that appeared only once in a century.
Dry weather means more dead trees, shrubs and grass – and more fuel for fire.
"All these extremely dry years create an enormous amount of damaged biomass," said Misel Vennetier, an engineer from France's National Research Institute for Science and Technology for the Environment and Agriculture (IRSTEA).
"It's perfectly flammable."
To make things worse, new species that are better suited to semi-arid conditions are growing in their place.
"Plants that like moisture disappear, they replace them with flammable plants that can withstand dry conditions, such as rosemary, wild lavender and thyme," Vennetier said.
"The change is going pretty fast."
With rising livestock and less rain, trees and shrubs under the stress of water send the root deeper into the earth, sucking every drop of water that can nourish the leaves and needles.
This means that the humidity on the ground that could help slow down the fire that passes through the forest or garage is no longer there.
In the temperate zone of the northern hemisphere, the fire was historically short – in July and August, in most places.
"Today is the period that is subject to fires extended from June to October," said scientist Thomas IRCTEA Thomas Curt, referring to the Mediterranean basin.
In California, which only recently emerged from a five-year drought, some experts say that there is no longer a season – fires can occur all year round.
"The warmer they get more lightning," said Mike Flannigan, professor at the University of Alberta, Canada, and director of the Western Partnership for Firearms.
"Especially in northern areas, it turns into more fires."
At the same time, he noticed that people are launching 95 percent of the world's fire.
Bad jet stream
The normal weather patterns in North America and Eurasia depend to a large extent on powerful high-altitude air currents – produced by the contrast between polar and equatorial temperatures – known as jet streams.
But global warming has raised the temperature in the Arctic twice as fast as the global average, weakening these currents.
"We see extreme weather conditions because of what we call blocked ridges, which is a high-pressure system in which the air is tone, becomes warmer and drier along the road," Flannigan said.
"Firefighters have known for decades that they are suitable for firefighting activities."
Climate change not only increases the likelihood of fire, but also their intensity.
"If the fire becomes too intense," as it is now in California, and in Greece last summer, "there is no direct measure you can take to stop," Flannigan said.
"It's like spitting on fire."
With rising temperatures, the rows moved north into Canadian boreal forests, causing desolation – and killing trees – along the road.
"Bleeding larvae of the bug temporarily increases the flammability of the forest by increasing the amount of dead material, such as needles," Villiams said.
Globally, forests account for about 45 percent of Earth's coal and absorbs a quarter of the emissions of harmful gases.
But as the forests die and burn, some of the carbon returns to the atmosphere, contributing to climatic changes in the embrace that the scientist called "positive feedback". – AFP