Climate change made LA fires worse, scientists say

Climate change was a major factor behind the hot, dry weather that gave rise to the devastating LA fires, a scientific study has confirmed.

It made those weather conditions about 35% more likely, according to World Weather Attribution - globally recognised for their studies linking extreme weather to climate change.

The authors noted that the LA wildfire season is getting longer while the rains that normally put out the blazes have reduced.

The scientists highlight that these wildfires are highly complex with multiple factors playing a role, but they are confident that a warming climate is making LA more prone to intense fire events.

"Climate change increased the risk of the devastating LA wildfires," said Dr Clair Barnes, from Imperial College London, the study's lead author.

"Drought conditions are more frequently pushing into winter, increasing the chance a fire will break out during strong Santa Ana winds that can turn small ignitions into deadly infernos."

The Santa Ana winds are strong and gusty east or north-easterly winds that blow from inland California towards the coast.

Around 30 people have died and more than 10,000 homes have been destroyed in the fast-spreading, destructive fires that broke out in early January.

This new study looks at what are termed the fire-prone conditions that can lead to dangerous conflagrations.

It's been carried out by a team of researchers from World Weather Attribution (WWA), a global group that publishes rapid analyses of climate-related weather events.

They use climate models to simulate how the warming that has occurred since the middle of the 19th century is influencing heatwaves, droughts, floods and fires.

The widespread burning of coal, oil and gas in the wake of the industrial revolution has driven billions of tonnes of planet-warming gases into the atmosphere.

Acting like a blanket, these gases have driven up temperatures by around 1.2C since then.

By using climate models and statistical methods along with real world observations, the WWA group have been able to show how much of an influence climate warming has had on extreme events.

In the case of the LA fires, they found that the hot, dry conditions that drove them are expected to occur once every 17 years.

This is an increase in likelihood of around 35% compared to a world that hadn't experienced warming.

"We actually see that the models show very much the same results that the [real world] observations have," said Dr Friederike Otto, the head of World Weather Attribution.

"So there, in this combined index, we are quite confident about the result... we have actually a signal that we can say that we definitely can attribute that, also quantitatively."

The researchers also examined other important variables that can lead to wildfire including the length of the fire season.

By analysing weather observations, the scientists found that this has increased by around 23 days since the world began warming, around 1850.

The team say that this means the dry conditions and the Santa Ana winds that are crucial for the spread of fires, are increasingly overlapping.

Another key element is drought.

Dry conditions in the LA area over the October to December period are now about 2.4 times more likely than before humans starting using fossil fuels on a large scale.

The researchers are clear that climate change increased the probability of the hot, dry conditions that gave rise to the fires.

However, the authors are more cautious about the link between rising temperatures and the longer fire season or decreased rainfall, saying that the models did not show a significant connection.

Despite these reservations, the conclusion is that a warmer world increased the chances of the devastating wildfires occurring - as more fossil fuels continue to be burnt, those chances will continue to rise.

"Overall the paper finds that climate change has made the Los Angeles fires more likely despite some statistical uncertainty," said Prof Gabi Hegerl, from the University of Edinburgh, who was not part of the study team.

"This is a carefully researched result that should be taken seriously," she said in a statement.

The new work builds on research that was published while the fires were still burning fiercely.

That study linked the wildfires to what's termed "climate whiplash."

The idea is that very wet years are followed almost immediately by very dry ones, which increases the risk of fires.

This is what happened in LA, when two wet winters were followed by an extremely dry autumn and winter this year – the wet weather promoted the growth of grass and shrubs that became the fuel for the fires that took off in the gusting Santa Ana winds.