At least 25 dead, an area almost equivalent to Ireland gone up in smoke, several thousand houses reduced to ashes, tens of thousands of inhabitants evacuated, millions of animals killed ... The dramatic toll of fires in Australia , which have been raging since September, could get even heavier as authorities have warned that the disaster may continue for weeks or months. Summer on the mainland ends in late February.

Australia is known to be the country most affected by forest fires in the world. Heat, drought and fires are recurring phenomena during the southern summer. But how to explain their precocity and their intensity this year? While Australian Prime Minister Scott Morrison, a staunch defender of the coal industry, took several weeks to recognize that these extraordinary fires could be linked to global warming, scientists speak of an "undeniable link".

To explain these exceptional fires, Nerilie Abram, professor at the Australian National University in Canberra, and author in charge of coordinating a special report from the IPCC (Intergovernmental Panel on Climate Change) described on the site from The American Scientist an "explosive cocktail", combining global warming with years of drought as well as other climatic factors such as wind speed or humidity. Clearly: global warming does not in itself cause these particularly violent fires, but can make weather conditions more favorable.

"Fires are established in places that would not normally burn"

According to the Bushfire and Natural Hazards CRC, average temperatures in the country have indeed risen by more than 1 ° C since the start of the industrial era. "Eastern Australia has been drought since 2017, says the Australian researcher. The severity of the current drought has caused the death of vast areas of vegetation. It has even dried up tropical rain forests, allowing violent fires to settle in places that wouldn’t burn normally. " Monday, January 6, the mercury still exceeded 40 ° C throughout the territory, with a record at 47 ° C in the state of Western Australia.

Southeast Australia has warmed around 1.5C since the late 1800s. Climate models do a good job of reproducing this historical trend, and project an additional 1.5C (+/- 1C) of warming by 2100 under a medium-high emissions scenario (RCP6.0): pic.twitter.com/0J7sksunpo

- Zeke Hausfather (@hausfath) January 5, 2020

The Indian Ocean dipole slowed down the rains

This is mixed with the Indian Ocean dipole, better known as the Indian El Niño, which corresponds to the variation of the temperatures of the Indian Ocean surface between its eastern and western part: "The main guilty of our current conditions [...] is one of the most positive Indian Ocean dipole events (DOI) ever recorded, "commented Dr. Watkins, director of long-term forecasting at the Australian Bureau of Meteorology, adding: "A positive DOI means that we see fewer weather systems carrying rain and warmer temperatures than average in large parts of the country."

Another factor was also decisive: a sudden and rare stratospheric warming over Antarctica at the end of winter, increasing the risk of forest fires in eastern Australia. "Indeed, a northward movement in the west winds from the southern hemisphere at this time of the year causes very hot and dry west winds across the continent," said Professor Nerilie Abram.

"The summer of anger was predictable"

"The country is burning," sums up Nerilie Abram, but "the summer of anger" was, according to her and many Australian climatologists, "predictable". On the one hand because global warming increases the risk of fires: "Many scientific studies have revealed clear links between the hottest and driest years and the largest burned areas, especially in California and Australia" , provides France 24 Zeke Hausfather, director of climate and energy at the Breakthrough research institute, specializing in technological solutions for environmental problems.

Scientists have given clear warnings to policy makers for decades on the increased fire risk that climate change would bring.

Thread by @ KetanJ0 shows some of this. No excuses, our governments knew but didn't act. Even worse, they spread misinformation instead. https://t.co/hbeexeh2ep

- Teacher. Nerilie Abram (@dr_nerilie) January 5, 2020

On the other hand, because scientists had predicted for decades the increase in the number of forest fires in Australia. Zeke Hausfather cites in particular the IPCC's fourth evaluation report dated 2007, which already predicted that "heat waves and fires will increase practically in intensity and frequency" in the country during the 21st century.

Beyond the climatic part which is difficult to control, scientists assure that the control of bushes would reduce the frequency of fires. "Efficient forest management and clearing can reduce the intensity of the flames," says Zeke Hausfather. The latter deplores "the accumulation of undergrowth" in the last ten years, which have become particularly flammable. "To cope with the forest fires we have today, we need to encourage people to live in areas less prone to fire," he concludes.

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