The deadly heat waves, floods, and droughts that are upending the lives of thousands of people, from the American West to southern Europe and central China, will likely only get worse as global temperatures continue to rise, according to a sobering new report on the state of the world’s climate.
California's Dixie Fire, currently the second largest in the state's history, has scorched nearly 500,000 acres, leveled over 400 homes to date, and threatens thousands more. The fire's exact cause is unknown, but it's being fueled by extremely dry conditions and strong winds.
Scientists have long theorized that climate change is associated with widespread changes in weather patterns. But the sixth report by the UN’s Intergovernmental Panel on Climate Change (IPCC), published on Monday, makes the strongest case yet that human-caused climate change is to blame. Already, the world has warmed 2 degrees Fahrenheit (1.1 degrees Celsius) since the industrial age, and extreme weather is one of the most prominent ways that warming manifests itself.
“We can link extreme weather to climate change in the same way we can link smoking to cancer,” says Friederike Otto, one of the report’s authors and a climate change researcher at Oxford University.
And, like smoking, the damage is hard to reverse, Otto says. If all greenhouse gas emissions ceased today—a planetary version of quitting smoking—the worsening heat waves and floods occurring now would be locked in for centuries. What’s most important, scientists say, is making sure these events don’t grow even more common and intense than they are now.
What do we know and how do we know it?
The report’s findings on extreme weather are based on hundreds of peer-reviewed scientific papers and represents the scientific community’s latest consensus on the state of climate change. The first report was published in 1990, the most recent in 2013.
In the seven years since, the influence climate change is having on extreme weather has become clearer, scientists say. While the 2013 report mentioned extreme weather only in passing, the latest iteration devotes a chapter to it.
“I feel strongly that the public needs to know that dangerous climate change is here and now,” says Michael Wehner, an extreme weather researcher at the Lawrence Berkeley National Laboratory. Wehner wrote extreme weather projections for the 2013 report and is a lead author for the report out today.
For the first time, the report details the effects of climate change by region, and shows that nearly every country on the planet will be hit by intensifying heat waves, more rainfall, or worsening drought. In July, parts of China saw 25 inches of rain in a single day—the amount of rain that typically falls in a year.
The report also notes that tropical cyclones (the weather pattern known as hurricanes in the Atlantic Ocean) will change character: They’ll become more powerful, move more slowly over land, and drop so much more rain that flooding will often cause more damage than the wind. In the United States, Texas and the Carolinas have already experienced this new type of hurricane—Hurricane Harvey in 2017 and Hurricane Florence in 2018 led to catastrophic floods and billions in damages.
“All regions of the world are affected by some extremes. Changes are happening everywhere,” says Sonia Seneviratne, an environmental scientist at the Institute for Atmosphere and Climate in Zurich and one of the IPCC report’s authors. “They're also multiplying with increasing global warming.”
Many regions around the world are now seeing “compound events,” she says. Wildfires are breaking out in areas suffering from heat waves and drought. Or heavy rainfall in coastal areas exposed to rising seas, for example, compounds the severity of a disaster.
After grappling with drought and record-breaking heat, California is now seeing its second largest wildfire on record. Turkey and Greece, facing one of the worst heat waves on record, also are battling dramatic wildfires.
To determine how much rising temperatures are increasing the odds of an extreme weather event, scientists model how a weather pattern would have evolved in a climate without high levels of planet-warming emissions. Heat waves and extreme rainfall have the clearest influence from climate change because their increase can be directly linked to rising temperatures. Other types of extreme weather, such as dangerous winter storms and tornadoes, are still active areas of research with less conclusive findings.
While raising the global temperature by a degree or two may sound minor, not all regions of the world are warming equally. In the Pacific Northwest, for example, where historic heat waves this summer killed an estimated 800 people, temperatures in 2050 are expected to be 5.8°F hotter than they were before the industrial revolution. That not only raises average temperatures, it also raises the average extreme.
“Climate change is making heat waves orders of magnitude more likely,” says Otto. A study she and her peers from an initiative called World Weather Attribution found that the Pacific Northwest’s heat wave would have been “virtually impossible” without climate change.
“In rainfall, you see maybe a doubling [of the odds]. For heat waves you easily see an increase by a factor of 10 or more, and so I think heat waves are really one of the most striking impacts of climate change,” she says.
Anomalous heat waves that formerly had a chance of occurring once every 10 years are now more than twice as likely to occur. Even rarer heat waves, likely to have hit once every 50 years, are nearly five times more likely, according to the IPCC.
What do we do about it?
The IPCC report comes ahead of a November conference where nearly 200 countries will meet in Glasgow, Scotland to negotiate ways to reduce their emissions. Current policies from countries around th globe have the world on track to reach 3°C of warming by 2100.
To limit global warming to just 2°C , Wehner says, “It’s my feeling we would have to do something rather drastic.” Something drastic, he adds, means completely eliminating consumption of coal, oil, and natural gas.
Even if the world’s nations were to completely stop emitting carbon dioxide, methane, and other emissions warming the planet today, the effect of just the 1.1°C of warming that has happened would linger for a millennia. What’s important now, says Wehner, is trying to prevent further damage.
“If you thought this summer was bad, a summer under a 3°C or 4°C warmer world would make this summer feel relatively normal,” says Wehner. “It’s hard to imagine how bad it would be. Some parts of the world would not be livable. The biggest hurricanes would be just devastating.”
While this IPCC report looked at the physical science of climate change, another iteration will publish in February 2022. That one will examine the effect climate change is having on humans, and how we need to adapt.
From 2000 to 2015, as many as 86 million people moved into regions where flooding is common, according to a study recently published in Nature. The combined effect of rising sea levels and heavier precipitation will mean even more people will be exposed to floods in the future. Without effective adaptation, that means more people will be facing serious risk.
“The term ‘natural disaster’ is used very frequently to describe things like hurricanes. Disaster researchers have for many decades argued that the term is a misnomer,” says Samantha Montano, an emergency management expert at Massachusetts Maritime Academy.
She contends that many disasters happen by design, a result of building vulnerable homes in at-risk locations, and without proper emergency management protocols in place. As the risks grow higher, she says, more funding to help people adapt is urgently needed.
“We have for a long time talked about climate change as something for future generations to deal with. We are already dealing with this. There are already people who have lost their lives,” says Montano.
The most vulnerable members of society will bear the biggest brunt of a more extreme climate—those unable to afford air conditioning or a car to evacuate in, says Montano. “As we watch these disasters unfold, it needs to be front-and-center in our narrative that this is not inevitable.”
Seneviratne cautions that even with action taken to adapt to current climate conditions, reducing emissions to avoid even worse climate extremes will be crucial.