Shifting Climate Normals Reflect a Warmer World

The release of updated U.S. Climate Normals, based on weather data from 1991 to 2020, provides a clear indication of a changing climate. These Normals, 30-year averages of key climate observations, serve as a benchmark for comparing current weather conditions and forecasting seasonal trends. The latest update, released by NOAA’s National Centers for Environmental Information in early May, reflects a warming trend compared to previous calculations.

What are Climate Normals?

Climate Normals are essential tools for a wide range of applications, from daily weather reports to long-term seasonal forecasts. They represent the average weather conditions for a specific location, calculated over a 30-year period. These averages are corrected to account for inconsistencies in data collection and changes in weather station locations over time. The Natural Resources Conservation Service provides further information on these calculations.

The Impact of Global Warming

The shift in baseline periods for Normals—from 1971-2000 to 1981-2010, and now to 1991-2020—has revealed a noticeable warming trend. The new Normals are not adjusted to remove the effects of global warming; instead, they reflect the changing climate. NOAA confirms that global warming is demonstrably affecting these calculations.

Changes Observed in Planting Zones

One visible consequence of the warming trend is the shift in U.S. Climate-related planting zones. Between the 1971-2000 and 1981-2010 Normals, many areas experienced warmer overnight low temperatures, leading to a northward and upward shift in plant hardiness zones. This indicates that regions can now support plant life that previously could not survive in those locations.

Recent Trends in Precipitation and Extreme Weather

Analysis of recent Normals data suggests a trend toward wetter conditions nationally. The National Weather Service notes that the 1961-1990, 1971-2000, 1981-2010, and 1991-2020 Normals represent the four wettest periods in the collection of data.

Understanding the Significance of Shifting Normals

The continuous updating of Climate Normals is crucial for accurately assessing climate trends and adapting to a changing world. While the Normals themselves don’t predict the future, they provide a valuable baseline for understanding how climate conditions are evolving and for making informed decisions in areas such as agriculture, water management, and public health.