LOUISVILLE, Ky. (WAVE) - Before we get into the nitty-gritty of the changes coming to climate normals, it’s important to define what climate is.
Climate applies to long-term regional or global averages of temperatures, rainfall, and humidity across years or decades. Typically, scientists use 30-year averages when defining climate normals. Thirty years is the standard set by the World Meteorological Organization in 1935, beginning with 1901–1930. A thirty-year time frame is seen as a long enough time frame for annual and multi-year climate variations to be negated.
The current batch of climate normals used by the National Oceanic and Atmospheric Association (NOAA) covers 1981 from 2010. The data is taken from observations made at around 9,800 stations across the United States run by the National Weather Service.
NOAA’s National Centers for Environmental Information (NCEI) has been collecting and analyzing weather and climate data from the past 30 years across the United States. This data from 1991 to 2020 will serve as the new climate “normals” for the next decade.
The climate normals are not just the averages of data. Calculating normals is much more complicated. They fill in missing data using information from nearby weather stations and make sure that daily and monthly normals match, according to NOAA.
NCEI revealed that there will be some small changes to how the climate normals are calculated. How numbers are rounded, output formatted, percentiles calculated, and numbers of days exceeding particular thresholds, are some of the changes that will be seen.
The data will also include 15-year normals for scientists to get a better representation of climatology closer to our current time.
The new set of normals will also lead to fewer “above normal” temperature days across the country for the beginning of this decade, compared to other years. Since the baseline is changing, that automatically leads to changes in comparisons.
Updating the climate normals is also very important when diagnosing certain weather phenomena. El Nino and La Nina are defined based on central and eastern Pacific Ocean sea surface temperatures and if they are running cooler or warmer than a seasonally adjusted average. Without an update to climate normals, warming that lasted an extended period may be mistaken for a permanent El Nino.