Hurricane Fiona is a harbinger of climate future

For the second time in five years, Puerto Rico has been blasted with a massive hurricane, causing widespread flooding and power outages, and the increasing severity of these storms is caused by climate change, according to studies.

The island, a U.S. territory that has still not fully recovered from Hurricane Maria in 2017, was hit by Hurricane Fiona on Monday. Parts of Puerto Rico received 30 inches of rain, causing landslides and overflowing rivers. Some rural roads have become impassable and have stranded residents. As of Tuesday morning, 1.17 million of Puerto Rico’s 1.47 million utility customers were without electricity, according to estimates from

Hundreds of Puerto Ricans have been forced from their homes, and the storm is gaining strength as it moves eastward to the Dominican Republic and north to the Turks and Caicos Islands. The U.S. National Hurricane Center warned of "life-threatening" flooding in those nations on Tuesday. Now a Category 3 storm, with winds reaching 115 miles per hour, it has caused deaths in Puerto Rico, the Dominican Republic and Guadeloupe.

The Caribbean has always experienced hurricanes in late summer, but the storms have become more intense, on average, as a result of global warming. For each additional degree Celsius (1.8 degrees Fahrenheit) of temperature, the air holds 7% more moisture. More water in the air leads to stronger storms. According to NASA, the average global temperature has risen by 1.1 degrees Celsius (2 degrees Fahrenheit) since the Industrial Revolution, as humans have emitted heat-trapping gases by burning fossil fuels.

Storms are also made stronger by warmer ocean temperatures, which provide the energy that powers hurricanes.

Two women point toward a river next to a house destroyed by flooding.
Two women stand next to a house destroyed by a river flood in the aftermath of Hurricane Fiona in Guayama, Puerto Rico, on Tuesday. (Ricardo Arduengo/Reuters)

A research paper published in April in the journal Nature Communications examined rain in the 2020 Atlantic hurricane season, one of the most active on record, and found that climate change caused a 10% increase in rainfall during the heaviest three-hour period of storms. Hurricanes are also featuring faster wind speeds, according to NASA.

Last year, a study of satellite images going back to 1979, published in the Proceedings of the National Academy of Sciences, showed that climate change had increased the chance that a hurricane would reach Category 3 or higher by roughly 8% each decade. A Category 3 hurricane is defined as one with sustained winds of at least 110 mph.

“The trend is there, and it is real,” James P. Kossin, a researcher with the National Oceanic and Atmospheric Administration and the lead author of the study, told the New York Times. “There’s this remarkable building of this body of evidence that we’re making these storms more deleterious.”

A flooded street after the flooding looks like a canal.
A flooded street in Catano, Puerto Rico, on Monday. (AFP via Getty Images)

It’s not that more rain will necessarily fall in total over the course of a year, but that rain is becoming more concentrated in specific extreme events, in between which many areas of the world are experiencing devastating droughts. (Current drought-stricken areas include the American West, much of Europe and the Horn of Africa.)

That’s why, in the last few decades, a higher proportion of total precipitation has come from extreme single-day heavy rains. Other parts of the United States have recently experienced this phenomenon, which can lead to deadly flash floods. Earlier this summer, three different areas were hit with “1-in-1,000-year rains” — a name derived from the fact that they are expected to occur only once in 1,000 years on average — in one week. Southern Illinois received 8 to 12 inches of rain in 12 hours. Six to 10 inches fell in seven hours in St. Louis, and up to 14 inches were recorded in eastern Kentucky, causing 39 deaths.

According to data from the U.S. Global Change Research Program, the Midwest gets 42% more heavy precipitation events per year than it did 60 years ago, and the Northeast gets 55% more.

A sailboat on its side, dragged to the shore by strong waves.
A sailboat dragged to the shore by strong waves after the passage of Hurricane Fiona in Samana, Dominican Republic, on Tuesday. (Erika Santelices/AFP via Getty Images)

Alaska was battered by a typhoon on Friday, washing away roads and causing power outages. The floodwaters began to recede on Sunday.

“For years, scientists have expressed concern that climate change has set the stage for greater impacts from large nontropical cyclones in Alaska,” the Washington Post noted.

Calling the storm “unprecedented,” Gov. Mike Dunleavy, a Republican, declared an emergency on Saturday in the face of the storm.

It may have been unusual in the past, but coastal areas from Alaska to Puerto Rico should expect that more extreme storms will be headed their way in the future.