In 2021, disasters continued to strike, from Hurricane Ida’s devastation in Louisiana and the Northeast to devastating wildfires in the West and damaging storms, tornadoes, and floods. Drought affected nearly half of the United States, and extreme temperature spikes disrupted power supplies just when people needed cooling or heating the most.

The costliest weather and climate disasters in the United States in 2018 caused an estimated US$145 billion in damage and claimed at least 688 lives, according to the National Oceanic and Atmospheric Administration on January 10, 2022.

2021 was also one of the hottest years on record globally, and the fourth hottest year in the United States in 127 years. Global warming does not cause every weather event, but rising temperatures affect the climate in ways that amplify heat waves and droughts and can supercharge storms. Much of the temperature rise is due to greenhouse gases accumulating in the atmosphere as a result of the combustion of fossil fuels.

During the disasters of 2021, one feature that stood out was a sharp precipitation divide in the United States: while most of the west was in severe drought or worse, with dry vegetation fueling fires, much of the eastern half of the country was getting soaked.

In August, heavy rains caused flash floods across Tennessee, sweeping away homes and vehicles and killing 20 people. A few days later, Hurricane Ida’s remnants crossed the country and hit New York City with record-breaking rainfall, submerging subway stations and basement apartments and killing dozens more.

Damage from the western drought was much more difficult to calculate on the other side of the country. The extreme dryness forced the closure of a key hydroelectric power plant in California for five months, harmed farms and ranches, and resulted in the first federal water use restrictions for the Colorado River as reservoir levels dropped.

Hurricane Ida, which grew from a weak hurricane to a Category 4 storm over warm water in the Gulf of Mexico, was the most costly disaster of 2021, with damage in Louisiana and then in the Northeast estimated to cost around $75 billion.

Because hurricanes are powered by warm water, rising surface temperatures will have an impact on them. Climate models predict that Atlantic hurricane rainfall and intensity will increase, but that the number of storms will not necessarily increase.

In February, an Arctic blast swept through the country’s center, bringing ice, snow, and subzero temperatures. The cold snap quickly turned into a human disaster in Texas. The cold weather overwhelmed Texas’ power grid, causing natural gas plant components to freeze and slowed natural gas supplies. The state’s power was out for an estimated 69 percent of the time, and NOAA reported 226 deaths. The storm has been blamed for 246 deaths, according to state officials.

The cold wave was the second-most expensive disaster in the United States in 2021, with costs estimated to be around $24 billion. While it may appear counterintuitive, rapidly warming temperatures in the Arctic can cause the jet stream to dip southward, causing a strong band of winds to form at the boundary between colder and warmer air. Changes in the Arctic are followed by changes in the stratospheric polar vortex, which are followed by cold waves in North America and Asia, according to research by atmospheric scientists Mathew Barlow at the University of Massachusetts Lowell and Judah Cohen at MIT.

The West’s heat and aridity exacerbated more multibillion-dollar disasters. On December 30, when Colorado would normally be blanketed in snow, a wildfire whipped by strong winds ripped through neighborhoods in unusually dry Boulder County. In a matter of hours, nearly 1,000 homes and several businesses were destroyed.

The blaze came after a series of devastating fires in California this summer. The total cost of damage from the 2021 Western fires was estimated to be $10.6 billion.

Forest managers are dealing with increased wildfire risks and costs as global temperatures rise and dry out vegetation. Fighting massive wildfires, such as the Dixie and Caldor fires in California that destroyed much of Greenville and Grizzly Flats in 2021, depletes funds needed for fire prevention efforts, such as forest thinning and prescribed burns, according to Susan Kocher and Ryan Tompkins of the University of California.

Tornadoes, like the deadly outbreak that caused another multibillion-dollar disaster across Kentucky and neighboring states in early December, haven’t been definitively linked to global warming, but climate models can still provide some insight, according to Central Michigan University meteorology professor John Allen.