Thousands of lightning strikes have sparked hundreds of fires across California in recent days, producing several major clusters burning around the San Francisco Bay Area. The blazes quickly ripped through hundreds of thousands of acres, forcing thousands to evacuate, filling the skies with smoke, and raining down ash across much of the region.

The fires followed a bone-dry winter in Northern California and a stretch of record-setting summer heatwaves across the State; conditions that effectively turned grasslands and forests into tinder. The infernos come on the heels of several of the most destructive and deadly fire seasons in California history; all of which raises the question, once again: Is human-driven climate change to blame? Did it make the latest fires more likely or more severe? Climate scientists, who long resisted linking global warming to any specific extreme event now say its influence is all but certain.

But so-called extreme weather attribution studies have clearly and repeatedly found that climate change exacerbates heat waves, which help create the conditions for wildfires to burn intensely and spread rapidly.

“The answer is always that climate change plays a large role in the severity or likelihood [of heat waves],” he says. Over the last four decades, the combined forces of higher temperatures and lower precipitation levels have already doubled the risk of extreme wildfire conditions in California during the fall, according to a recent paper in Environmental Research Letters that Swain co-authored. And unless the world begins cutting emissions significantly and soon, the odds could double again in the coming decades, the researchers found.