The Great Plains were already crackling with the blazes of an unusually early fire season last spring when federal officials, warning of the costly impacts of climate change, asked Congress for help with overstretched firefighting budgets.
Nobody could have foretold the ferocity of the fires that would close out 2017 in California.
In the Atlantic, ocean temperature maps were already colored in glaring hues by midsummer when hurricane forecasters heightened their alerts about a season that seemed likely to send more intense storms toward the Caribbean and the U.S. coast.
But no one imagined the record-shattering season that ensued, inundating Houston, dealing the Caribbean islands one devastating blow after another, letting Florida off with a narrow escape from a statewide calamity, and plunging Puerto Rico into darkness for months while it struggled to tally its dead.
The year's disasters, in human terms and also measured in dollars, put 2017 in the United States' record books. The costs to the federal government alone—still unpaid, as Congress struggled to close out its financial books at the end of the year—are likely going to run into hundreds of billions of dollars. Swiss Re estimated global economic losses from disasters in 2017 were about $306 billion, far above the average of the past decade.
Jerry Brown, the governor of California, called this "the new normal" as he surveyed the fire damage.
"This could be something that happens every year or every few years," he said.
Mitigate, Adapt or Suffer the Consequences
Past disasters have sounded similar warnings without changing America's political equations in ways that would attempt the deep reductions in emissions that science shows is necessary.
"A common feature of the hurricanes and the wildfires is that there have been many warnings from scientists and others," explained Kevin Trenberth, a climate scientist with the National Center for Atmospheric Research. "With climate change, one slows or stops the problem (mitigation) or adapts to the problem (builds resilience) or suffers the consequences. In Texas, Florida and Puerto Rico, and Santa Rosa, it is clear that the people have chosen the last option."
Take the tropical storms that lashed the United States—not to mention the one that, astonishingly, threw a strong left hook at Ireland—in 2017.
First, Hurricane Harvey camped over Houston with record rainfall over five days. Then Irma swept across the Caribbean and southeastern U.S., decimating some islands and inundating parts of Florida where sea level rise threatens to worsen floods in the future. After Irma dissipated, Maria devastated Puerto Rico; some investigations have put the death toll there over 1,000.
"The three storms—Harvey, Irma and Maria—were all enhanced," Trenberth said. "Bigger, stronger and longer lasting because of climate change as manifested through exceptionally high ocean temperatures."
Fine-Tuning the Science of Attribution
Climate researchers say it can be difficult to disentangle the effect of climate change on hurricanes, because natural cycles play a role from season to season. But the 2017 special science report from the U.S. Global Change Research Program, the most recent definitive review of climate science, says that human impacts have forced the upward trend in hurricanes since the 1970s and says "theory and numerical modeling simulations generally indicate an increase in tropical cyclone intensity in a warmer world."
Scientists are getting better at linking individual extreme weather events to longer-term global warming. And they are issuing their verdicts more quickly than in the past.
Already, there are two studies demonstrating that global warming substantially increased the odds of the flooding in Houston this year. More than 50 inches of rain fell in the span of a few days in parts of the area.
Fiery Signs of a Climate Changed
For years, scientists have been warning that global warming might set the American West on fire.
The signals that 2017 might be an especially fiery year started flickering early when blazes ripped across Texas, Oklahoma, Kansas and Colorado in March, a once-rare phenomenon that is becoming increasingly common in the Plains.
More than a thousand miles to the west, California confronted a series of climate-fueled weather events that successively made things worse.
First, the winter's "Pineapple Express"—a band of wet air from Hawaii—ushered in record rains, bringing apparent relief for a multi-year drought, but also causing flooding and mudslides.
Its side effects fueled the state's worst wildfire seasons on record. The rain brought a surge of lush green across the state. But when the rain stopped, as it does in California's Mediterranean climate, and temperatures headed upward to record levels, all that green turned brown—and then the fires started.
From April to December, fires burned more than 1 million acres across the state, killing at least 40 people, including the "wine country" fires in Sonoma and Napa Counties and late-season fires that tore through Southern California when the usual rains failed to arrive.
Research has attributed much of the recent drought to human-induced climate change. A study co-authored by Columbia University climate scientist Park Williams in 2016 found anthropogenic warming had doubled the amount of forest burned in the West since 1984.
Two Scenarios—Both Bad—for California
But there's conflicting research on just how climate change will affect snow and rain in the state.
But another recent study found that melting Arctic ice could mean a drop in California's precipitation by 15 percent over the next 20 to 30 years.
Either scenario is bad news.
Less rain would generally mean drier conditions overall—a fire risk, especially in forested regions. More rain would mean more fuel, including grasses in heavily populated coastal areas, that would dry out later in the year.
"A higher frequency of wet winters would coincide with a higher frequency of hot summers," Williams warned.
Williams and others noted, however, that other factors—especially wind—drove the California fires. But the wind is just one of the factors, along with dry vegetation, scant rain, and high temperatures, Williams explained. And the destructive blazes of 2017 happened because "all the switches are on."