PARIS, November 12 – Deadly fires, such as the poor in northern and southern California, have been widespread in recent years throughout the country and around the world. AFP spoke to scientists about how climate change could be worsening.
Other factors have also contributed to the frequency and intensity of large fires, including human intervention in forest lands and the questionable management of forests. "The patient was already sick," said David Bowman, professor of environmental biology at Tasmania University, and a natural disaster expert.
"But climate change is accelerating."
Good weather fire
Any firefighter can tell you a "good fire" recipe: hot, dry and windy.
It is not surprising that many of the tropical and temperate regions that have devastated forest fires are those that are projected in climate models to see higher temperatures and more drought.
"In addition to drought and hotter air pollution, climate change – through increased evaporation rates and droughts – also creates a more flammable ecosystem," said Christopher Williams, Health Sciences Director at Clark University in Massachusetts.
Over the past 20 years, several drought times have taken place in California and Southern Europe, which occurred only once a century.
Dry weather means more dead trees, shrubs and grass – and more fuel fires.
"All these extremely dry years produce a huge amount of dry biomass," said Michel Vennetier, engineer at the French National Environmental and Agricultural Science and Technology Research Institute (IRSTEA).
"It's perfectly flammable."
In order to make the situation worse, new species that are better suited to semi-dry conditions are growing instead.
"Plants that resemble moisture have disappeared, replaced with more flammable plants that can withstand dry conditions, such as rosemary, wild lavender and thyme," said Vennetier.
"The changes are fairly fast."
Suddenly the plants
With increasing mercury and less rain, water stress trees and shrubs send roots deeper into the soil, draining off every drop of water that they can feed on leaves and needles.
This means that the moisture of the land, which may have helped slow down the sweeping of the fire through the forest or the gutter, is no longer there.
The temperate zone of the northern hemisphere was historically shorter in July and August in most sites.
"Today, time sensitive to fires, extended from June to October," said IRSTEA scientist Thomas Curt, referring to the Mediterranean basin.
In California, which only recently appeared after five years of drought, some experts say there is no longer a season – fires can take place throughout the year.
"The warmer it gets, the more lightning is," said Mike Flannigan, professor at Alberta University, University of Canberra and director of the Wildland Fire Science Western Partnership.
"Particularly in the northern areas that are more exposed to fires."
At the same time, he noted that 95% of the forest fires in the world began in humans.
Ordinary weather over North America and Eurasia depends to a large extent on the strong high air currents created by the contrast between the polar and equatorial temperatures, known as spray flow.
But global warming has raised Arctic temperatures twice as fast as the world average, which weakens these currents.
"We see more extreme weather conditions, because we call it blocked grooves, which is a high pressure system in which the air flowed, becoming warmer and drier along the way," said Flannigan.
"Firefighters have known for decades that they are fired."
Climate change not only increases the likelihood of forest fires, but also their intensity.
"If the fire gets too intense," as at that time in California and in Greece last summer, "there is no direct measure that you can take to stop it," said Flannigan.
"It's like spitting on a bonfire."
As the temperature rises, beetles have moved north to the Canadian boreal forests, destroying the damage and killing the trees on the way.
"The outbreaks of pea beetles temporarily increase the flammability of the forests by increasing the amount of dead material, such as needles," said Williams.
About 45 percent of non-carbonated land in the world is in the forests, accounting for a quarter of greenhouse gas emissions.
But when the woods die and burn, some of the carbon is released back into the atmosphere, promoting climate change in a vicious circle that scientists call "positive feedback." – AFP