Extreme weather in the U.S.: what federal assessments document, and where the evidence is weaker (2023-2025)

Case

The Fifth National Climate Assessment (2023) and NOAA's 2025 science fact sheet document increases in U.S. heat waves, heavy rainfall, rapid hurricane intensification and western wildfire, and the cost of weather disasters. They are less certain about hurricane and tornado frequency, and they say rising disaster costs reflect exposure and vulnerability as well as climate. This entry records which findings are well supported and which are not, so other entries can cite them accurately.

What the assessments treat as settled
The Fifth National Climate Assessment calls the evidence for warming incontrovertible and the science unequivocal that rising greenhouse gases are driving many observed trends. It concludes the only credible explanation for the observed warming is human activity.
Including Alaska, the continental U.S. has warmed about 60% faster than the planet as a whole since 1970.
Across 50 large U.S. cities, the average number of heat waves has doubled since the 1980s and the heat-wave season has lengthened from about 40 days to about 70 days.
Since the 1950s the number of extreme-precipitation days has risen about 60% in the Northeast and about 45% in the Midwest, and human-caused warming has contributed to heavier extreme rainfall across nearly 70% of the country.
Hurricanes have intensified more rapidly since the early 1980s, and the assessment notes slower-moving storms that can drop more rain.
In the West, human-caused warming accounted for nearly 68% of the observed increase in aridity from 1979 to 2020, which set conditions for larger burned areas. The assessment also lists fire suppression, land use and the loss of Indigenous fire stewardship as contributing factors.
In the 1980s the U.S. averaged one billion-dollar weather disaster every four months. By the 2010s it was one every three weeks or less.

Where the evidence is weaker
NOAA's January 2025 fact sheet says the IPCC has high confidence that human-caused climate change is the main contributor to more frequent and intense heat extremes and that it was likely the main driver of heavier rain for most land regions since the 1950s.
For hurricanes and tornadoes, the same fact sheet says there is no clearly detectable human influence to date on frequency and intensity trends at the global scale, apart from sea level rise.
Atlantic hurricane intensity has risen since 1980, but NOAA says the quantitative effect of human-caused greenhouse gases is uncertain because aerosol changes and natural variability also contributed. U.S. landfalling hurricane frequency has been stable since 1900.
The average annual number of U.S. tornadoes appears roughly constant, while outbreaks appear to be more frequent and tornado power may have increased. The assessment says observations of these events are incomplete.
NOAA says the human contribution to drought is hard to determine. There is no significant trend since 1900 in the percent of the U.S. in moderate to extreme drought, though the Southwest has been unusually dry since 2000.
The assessment attributes rising disaster costs in part to more frequent and severe extremes and in part to increased exposure and vulnerability.

Perspectives

Editorial read — The Author (site author)
That human activity is warming the planet is the best-supported finding in these assessments. The open questions are narrower: how much of a particular hurricane, tornado season or drought to attribute to warming. Uncertainty about those individual hazards is not uncertainty about the warming, and it should not be used to dismiss the main finding. The entries on this site cite the strong findings as strong and the weak ones as weak.

Research notes
Purpose: a reference entry so other entries cite extreme-weather trends accurately, separating well-supported findings from uncertain ones. Open leads: (1) NCA5 is from 2023; status of any later National Climate Assessment not checked. (2) Add wildfire acreage and heat-death figures from primary data if needed. (3) The 2025-26 EPA and NOAA cuts are covered in separate entries and should not be presented as the cause of trends measured over previous decades.

Note
Attribution of individual hurricanes, tornadoes and droughts to human-caused warming remains uncertain in these assessments; the warming itself and its human cause are not in doubt.

Sources
[1] Fifth National Climate Assessment, Chapter 2: Climate Trends (U.S. Global Change Research Program) (https://nca2023.globalchange.gov/chapter/2/) · 2023-11
[2] NOAA Science Council: State of the Science Fact Sheet, How Human-Caused Climate Change Affects Extreme Events (https://sciencecouncil.noaa.gov/wp-content/uploads/2025/03/SoS_Fact_Sheet_Climate_Change_Extremes_Jan_2025.pdf) · 2025-01

Connections

Related — Ocean observing under budget pressure: NOAA research cuts, Argo floats and the end of U.S. biogeochemical Argo (2025-2026)
That entry covers what federal assessments document about extreme weather; this one covers the ocean measurements that feed forecasts and climate research.

Related — The National Climate Assessment and USGCRP: dismissed authors, a dark website and a skeptic in charge (2025-2026)
That entry draws on the Fifth National Climate Assessment (2023); this one covers the dismantling of the program that produces the assessments.