Introduction
Summary Introduction Letter
The Climate Challenge*
Nearly every environmental indicator in the 2025 annual report has a tie to the climate. The trend over more than sixty years suggests that Connecticut’s climate is getting warmer, and precipitation is increasing.
The trend for annual heating degree days (HDD) is decreasing while the trends for annual cooling degree days (CDD) and growing degree days (GDD) are increasing from 1960 through 2025. HDD for 2025 (5,095) was 14 percent less than the annual average since 1961, while CDD (852) and GDD (3,215) for 2025 were three (3) and 4.5 percent greater than the annual average since 1961, respectively.
Annual precipitation for 2025 (46.6”) was one (1) percent greater than the annual average since 1960 (46.1”), while the number of days in 2025 with rainfall greater than one inch (12) was the same as the annual average since 1960. It is predicted that as the climate warms, severe weather events, such as drought conditions that impacted Fairfield, Middlesex, and New Haven Counties in 2025, and extreme rainfall, might become more frequent.2
The annual average temperature** for 2025 was about 52 degrees Fahrenheit (°F), which was higher than the average annual temperature from 1960 through 2025. The number of days with high temperatures greater than 90°F (18) was 20 percent greater than the annual average from 1960 to present (15). The trends for annual average temperature and 90°F days are increasing.
Technical Notes: Weather data measured at Bradley International Airport (BDL). **The vertical axis in the chart above has been shortened, beginning at 40 degrees Fahrenheit (°F) rather than the customary zero.
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1 National Oceanic and Atmospheric Administration (NOAA), National Weather Service, NOWDATA, Hartford-Bradley International Airport, Accessed January 7, 2026; www.weather.gov/wrh/Climate?wfo=box
2 Connecticut Department of Energy and Environmental Protection (DEEP), BUILDING A LOW CARBON FUTURE FOR CONNECTICUT ACHIEVING A 45% GHG REDUCTION BY 2030; portal.ct.gov/-/media/DEEP/climatechange/publications/BuildingaLowCarbonFutureforCTGC3Recommendationspdf.pdf#page=20.