The number of frost-free days in a year reflects the overall warming trend in the climate system.
The bars on the graph show the difference between the number of frost-free days in each year and the average number of frost-free days from 1979 to 2020.
Length of the Frost-free Season in the U.S. is Growing
Over the past 40 years, there has been an increase in the length of the frost-free season over the contiguous United States and Alaska, relative to the 1979–2020 average.
Why It's Important
Observed changes in the length of the frost-free season reflect the overall warming trend in the climate system.
The frost-free season can be an important factor in determining the potential growing season for vegetation. For instance, some pests and pathogens affecting forests and crops are projected to benefit from warmer temperatures and longer frost-free seasons.
This indicator can help decision makers understand and anticipate climate impacts on:
About Frost-Free Season
Global daily freeze-thaw data are provided by the National Aeronautics and Space Administration (NASA) Freeze-Thaw Earth Systems Data Record, which represents one of the longest continuous global records from satellite-based observations. Satellite microwave sensors are used to determine the frozen or thawed status of water on the land surface at a given time. Measurements are taken over the contiguous United States and Alaska and include all vegetated land areas where seasonal frozen temperatures are a major constraint to plant growth. Collecting these data over time provides information on the number of frost-free days in a given year.