The disasters just kept coming in 2021, from Hurricane Ida’s destruction across Louisiana and the Northeast to devastating wildfires in the West and damaging storms, tornadoes and floods. Nearly half the U.S. was in drought, and extreme temperature spikes disrupted power supplies just when people needed cooling or heating most.
In all, the costliest U.S. weather and climate disasters of the year did an estimated US$145 billion in damage and claimed at least 688 lives, the National Oceanic and Atmospheric Administration announced on Jan. 10, 2022.
As the disasters unfolded, scientists explained the influence of climate change. Here’s what they said about some of the costliest disasters of 2021.
Extreme rainfall in the east, drought in the west
One characteristic that stood out during the disasters of 2021 was a sharp precipitation divide in the U.S.: While most of the west was in severe drought or worse, with the dry vegetation fueling fires, much of the eastern half of the country was getting soaked.
Extreme downpours in August triggered flash floods across Tennessee that swept away homes and vehicles and killed 20 people. A few days later, the remnants of Hurricane Ida crossed the country and hit New York City with record-shattering rainfall that submerged subway stations and basement apartments, killing dozens more.
“Higher temperature increases evaporation from Earth’s surface, drying out vegetation and soils, which can fuel wildfires. It also increases the atmosphere’s capacity to hold moisture at a rate of about 7% per degree Celsius that the planet warms. With more moisture evaporating, global precipitation is expected to increase, but this increase is not uniform,” Wu wrote.
As the planet warms, wet areas are likely to get wetter, and dry areas drier, she said.
University of Miami oceanographer Nick Shay explained how the storm passed over a large pool of warm water in the Gulf of Mexico that had spun off from the Loop Current. That warm pool’s heat, extending down about 480 feet, fueled its strength.
That cold wave was the second-most expensive U.S. disaster of 2021, with costs estimated at around $24 billion.
While it may seem counterintuitive, rapidly warming temperatures in the Arctic can trigger this kind of southward dip of the jet stream, a strong band of winds at the boundary between colder and warmer air. Research by atmospheric scientists Mathew Barlow at the University of Massachusetts Lowell and Judah Cohen at MIT shows how that can happen as changes in the Arctic are followed by changes in the stratospheric polar vortex, which are followed by cold waves in North America and Asia.
“Our research reinforces two crucial lessons of climate change: First, the change doesn’t have to occur in your backyard to have a big effect on you. Second, the unexpected consequences can be quite severe,” they wrote.
The heat and dryness in the West contributed to more multibillion-dollar disasters. On Dec. 30, when Colorado would normally be blanketed in snow, a wildfire whipped by powerful winds tore through neighborhoods in abnormally dry Boulder County. Nearly 1,000 homes and several businesses were destroyed in a matter of hours.
The blaze followed devastating fires in California over the summer. Altogether, damage from the 2021 Western fires was estimated at $10.6 billion.
“To manage fires in an era of climate change, where drier, hotter weather creates ideal conditions for burning, experts estimate that the area treated for fuels reduction needs to increase by at least an order of magnitude,” they said.
Tornadoes, like the deadly outbreak that created another multibillion-dollar disaster across Kentucky and nearby states in early December, haven’t been clearly connected to global warming, but climate models can still provide some insight, as Central Michigan University meteorology professor John Allen explained.
“There are certainly signals pointing in the direction of a stormier future,” Allen said, “but how this manifests for tornadoes is an open area of research.”