Research & Developments is a blog for brief updates that provide context for the flurry of news that impacts science and scientists today.
After more than half a century of Earth Days, one planetary challenge—climate change—threatens our planet more than ever.
In 1970, the year Sen. Gaylord Nelson (D-Wisc.) organized the first Earth Day events, the annual average concentration of carbon dioxide in the atmosphere was 326 parts per million. In 2025, it was 31% higher, at 427 parts per million.
“It may sound small, but it’s reshaping daily life.”
Changes in average annual temperatures in U.S. cities and states show the powerful effects of this increase in heat-trapping carbon dioxide. A new analysis, published today by climate research and communications nonprofit Climate Central, found that since 1970, all 50 states and 99% of major U.S. cities have warmed, with an average city-level increase of 1.6°C (2.9°F).
“It may sound small, but it’s reshaping daily life,” Shel Winkley, a meteorologist at Climate Central, said in a video released alongside the report.
On average, the 49 U.S. states analyzed in the report have warmed by 1.7°C (3.0°F) since 1970. The six states that have warmed the fastest since the first Earth Day are Alaska with a 2.4°C (4.4°F) increase, New Jersey and New Mexico with a 2.1°C (3.7°F) increase, and Delaware, Massachusetts, and Vermont with a 2°C (3.6°F). Trends for Hawaii, which were analyzed separately and not included in the national average, also showed statewide warming.
In 2025, the United States was on average 1.4°C (2.6°F) warmer than the 20th century average. The Paris Agreement, a legally binding global treaty, sets a goal to limit warming to 1.5°C (2.7°F) above preindustrial levels, though some scientists expect that the world has already entered the period of time during which this limit will be breached.
Warming trends in the United States are most pronounced in the Southwest, where cities have warmed an average of 1.9°C (3.5°F) since 1970. And in some cases, cities are warming much faster than whole states. Three of the five cities that have warmed the fastest since 1970 are in the Southwest: Reno, Nev., with an increase of 4.4°C (7.9°F), Las Vegas, with an increase of 3.3°C (6.0°F), and El Paso, Texas, with an increase of 3.3°C (5.9°F).
Related
• Read the Climate Central Report: Fastest-Warming U.S. States and Cities
• Find Your City: Warming at All Levels
• We’re About to Reach the Paris Agreement Limit, If We Haven’t Already
• The State of the Science 1 Year On: Climate Change and Energy
The effects are evident at the national, state, and local levels. Temperatures have warmed in 240 of the 242 cities analyzed by Climate Central. Harrisonburg, VA and Monterey, CA were the only two cities analyzed that have not warmed since 1970.
The report highlights some good Earth Day news, however, and points out that solar and wind power generation is at an all-time high in the United States, accounting for 19% of the electricity generated in the country in 2025 despite those industries facing recent headwinds from the federal administration.
“Every fraction of a degree [of warming] that we prevent does matter, for our health, for our communities, and for the world that we’re passing on to the next generations,” Winkley said.
—Grace van Deelen (@gvd.bsky.social), Staff Writer
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