2021 Outpaced Years Past in Breaking All-Time Temperature Records

Temperatures in the United States last year set more all-time heat and cold records than any other year since 1994, according to a New York Times analysis of Global Historical Climatology Network data.

Heat waves made up most of these records. All-time heat records were set last year at 8.3 percent of all weather stations across the nation, more than in any year since at least 1948, when weather observations were first digitally recorded by the U.S. government.

The world has been warming by almost two-tenths of a degree per decade. Extreme-temperature events can often demonstrate the most visible effects of climate change.

“We do not live in a stable climate now,” said Robert Rohde, the lead scientist at Berkeley Earth, an independent organization focused on environmental data science. “We will expect to see more extremes and more all-time records being set.”

The brutal arctic outburst that caused Texas’ power grid to fail and the heat wave in the Pacific Northwest last June account for many of the new records.

During the winter storm, on Feb. 17, the temperature dropped to minus 5.98 degrees in Jacksonville, Texas, far below its normal February low of about 40 degrees. State officials in Texas said that 246 people died in the storm.

In Salem, Ore., the temperature spiked to 116.96 degrees on June 28. The normal high there in June is around 74 degrees. The National Weather Service has attributed at least 110 deaths to the extreme heat.

The Times analyzed temperature data from more than 7,800 weather stations across the United States. Locations without at least 30 years of weather data were ignored, though most stations have recorded temperature for at least 65 years.

All-time records have been set somewhere in the country every year since at least 1970, but 2021 stands alone when compared with recent years, a Times analysis found.

Heat waves in 2002 and 2012 brought unprecedented temperatures to hundreds of cities and towns. Like 2021, 2011 broke numerous cold and heat records. But last year’s extreme temperatures were spread across large areas of the country and surpassed even more records.

Numerous records set in 2021 were also broken by double digits.

To explain these extremes, Dr. Rohde made a comparison with world records in the 100-meter dash. Runners typically break world records by hundredths of a second.

Among the new temperature records, Dr. Rohde said, “it’s like someone came in and seemed to be running an entirely different race because they just blew past everything we’ve come to expect.”

New marks were also set by breaking records that have stood for decades. Bottineau, N.D., set a new minimum temperature record of minus 50.98 Fahrenheit, eclipsing tens of thousands of daily observations since 1893.

According to experts, climate change has pushed the extremes of temperature ranges around the world.

“What were hot days in the past are becoming more common,” Dr. Rohde said. “What were very, very hot days in the past are now two or three times more common than they used to be.”

Methodology

Data in the United States was obtained from the Global Historical Climatology Network (GHCN), an integrated database maintained by NOAA that contains daily climate summaries from land surface stations. The data was processed and analyzed with BigQuery.

The GHCN daily dataset acts as the official weather record of the United States, and it has been validated for spatial and temporal consistency across measurements. Daily observations that failed any quality checks were excluded, such as measurements that far exceed the lowest or highest temperatures ever recorded on earth.

A historical record is defined as the hottest or coldest temperature ever recorded up to that date. Only the hottest or coldest record for a particular year is compared. Other records in the same year, like, for example, during an extended heat wave, are excluded.

For every historical record, only stations that have collected a minimum of 30 years of data are used. Further, each station included in our analysis is required to have collected data for a minimum of half of its life span.

To compute historical records for cities, stations were aggregated to incorporated places as defined by the U.S. Geological Survey. Within each area, data across stations is treated as a unified measurement for calculating historical records. Records may differ slightly from other aggregated sources based on the specific regions and stations considered.