The devastating bush fires scorching Southern California offer a glimpse of a warmer and more fiery future, according to scientists and federal and international reports.
In the past three months, several studies and reports have warned that wildfires were getting bigger, that man-made climate change was to blame, and that it was only going to get worse, with more fires starting earlier in the year. While scientists are reluctant to blame global warming for any specific fire, they have been warning for years about how it will lead to more fires and earlier fire seasons.
"The fires in California and here in Arizona are a clear example of what happens as the earth warms, particularly as the West warms, and the warming caused by humans is making fire season longer and longer with each decade," said University of Arizona geoscientist Professor Jonathan Overpeck. "It's certainly an example of what we'll see more of in the future."
Since 1984, the area burned by the largest forest fires in the Western US - those of more than 400 hectares - has increased by 35,500 hectares a year, according to a study in Geophysical Research Letters. And the areas where fires are growing are areas where droughts have increased.
"That certainly points to climate being a major contributor", said the study's main author, geographer Professor Philip Dennison of the University of Utah.
The top five years with the most area burned all came in the last decade, according to US records. From 2010 to last year, about 2.6 million hectares a year burned on average; in the 1980s it was 1.17 million hectares.
"We are going to see increased fire activity all across the West as the climate warms," Dennison said.
That was one of a dozen "key messages" in the 841-page National Climate Assessment released by the US federal government earlier this month. It mentioned bush fires 200 times.
"Increased warming, drought and insect outbreaks, all caused by or linked to climate change have increased wildfires and impacts to people and ecosystems in the Southwest," the federal report said. "Fire models project more wildfire and increased risks to communities across extensive areas."
Likewise, the Intergovernmental Panel on Climate Change noted in March that bush fires were on the rise in the Western US, had killed 103 people in 30 years, and would likely get worse.
The immediate cause of the fires can be anything from lightning to arson; the first of the San Diego area fires seemed to start from sparks from faulty construction equipment, said California Department of Forestry and Fire Protection spokeswoman Lynne Tolmachoff.
But the California fires are fuelled by three major ingredients: drought, heat and winds. The first four months of the year have been the hottest on record in California and Arizona, according to National Weather Service records.
"With the drought this year, we're certainly going to see increased frequency of this type of event," Dennison said. "Because of the drought, the fuels [dry plants and trees] are very susceptible to burning."