The nation’s climate agency released new, 30-year climate “normals” for the United States Friday, and they do, indeed, show warmer average temperatures than the previous 30-year period.
But the implications of the data for long-term climate change are not as clear as they might seem at first glance.
Some of the warming seen in the 30-year averages, from 1981 to 2010, can be attributed to climate change, according to the National Oceanic and Atmospheric Administration.
But the 30-year averages are not designed to measure climate change. The new normals also result in part from location changes for weather monitoring stations, as well as changes in measurement methods and the instruments used.
“I would hesitate to attribute any one site to global warming,” said meteorologist Cynthia Palmer at the National Weather Service in San Diego County, which provides weather forecasts for Orange County. “For any one, given location, your normal can be similar, or slightly higher or slightly lower. They are just saying that on average, the trend is toward slightly warmer.”
The new normals drop the decade of the 1970s, and reveal that the newly added 2000s were about 1.5 degrees warmer on average than the 70s.
Meanwhile, the entire 30-year period is about 0.5 degrees warmer than the previous 30-year period.
NOAA recalculates the normals, used to place recent trends in context, every 30 years in keeping with the recommendations of the World Meteorological Organization, as well as a Congressional mandate to record U.S. climatic conditions.
The normals also track rainfall, snowfall, snow depth, dew point and other factors.
A better measure of long-term climate change, NOAA says, can be found in the U.S. Historical Climatology Network.