For the past decade, when a meteorologist in the US has said that a temperature or type of precipitation is above normal, they were comparing it to the average based on weather observations from 1981-2010. In May, a new average will be used, using data from 1991-2020. These new climate normals
show a warmer and wetter US.
“We’re really seeing the fingerprints of climate change in the new normal,” Palecki added. “We’re not trying to hide that. We’re in fact, reflecting that on the new normal so that we keep track of the climate, so people know what the climate is now. We use other data sets to show the climate change over time, but this is a really neat one to look at.”
Climate normals are a 30-year average of recent climate conditions, according to NOAA
. They provide the baseline for comparing weather and climate to the recent past.
When comparing the new 1991-2020 temperature average to the 20th century (1901-2000) average, it clearly shows most of the lower 48 states are much warmer now than in the past.
Breaking it down further by showing the 30-year temperature normals of the past century side-by-side shows “the huge difference in temperature over time as we go from cooler climates in the early 20th century to ubiquitously warmer climates here in the last two sets of normal,” said Palecki.
Although the warming trend is very clear in the longer-range comparison (1991-2020) compared to 1901-2000), not everyone will have a warmer temperature normal (1991-2020) compared to the last normal (1981-2010) when the new climate normals are put into operation.
Temperatures from 1991 to 2020 were generally warmer in most regions and the majority of seasons across the United States, but the North Central US was somewhat cooler than the 1981 to 2010 data, especially in the spring.
“Interestingly, this shift [to warmer normal] will result in there being fewer ‘above normal’ temperature days in most of the US at the start of this decade compared to recent years that used the previous normals cycle,” said Palecki.
Taking precipitation data and displaying the 30-year averages over the last century also reveals the influence of climate change, with a wetter trend.
“Precipitation normals have changed and varied from time to time, some periods drier, some periods wetter, but in the last three normals we’ve been driving toward a much wetter environment in most of the US,” said Palecki.
When comparing 1991-2020 precipitation normals to the 1981-2000 normals, there were notable large increases across much of the East, and distinct, season-dependent shifts were also observed in the West.
The nuance in the precipitation changes can get lost when averaging the entire year. Some locations may see wetter winters but drier summers, with little net change in annual average precipitation. These changes can create big impacts on natural ecosystems and agriculture that depend on precipitation at specific times.
Changes in intensity and type of precipitation can also occur without changing the annual total. More rain, less snow. Heavier downpours with longer dry spells.
Applying climate data to everyday life
Climate normals offer a wide range of applications beyond just weather and climate comparisons.
“These new normals are a better baseline for today’s climate, helping inform activities in many economic sectors,” said Palecki.
Power companies use climate normals to regulate energy load forecasting. Farmers benefit from the data for crop selection and planting times, while construction companies use them for planning and building design.
Local governments can use average snowfall for operation budget planning and monitoring water resources, and the new data will go into calculating various drought indices. These benefits extend to countless other industries and sectors.
The data is gathered from observations at nearly 10,000 weather stations across the US, operated by NOAA and the National Weather Service, and serves as the nation’s official climate normals for the next 10 years.
NOAA recommends an update each decade to climate normals, in part to incorporate newer weather stations coming online. However, the agency acknowledges that more recent updates are needed to keep pace with conditions as climate changes over time.
“This is why temperature and precipitation normals of means, totals and statistics often shift and change from one 30-year period to the next,” says Palecki.
The window of three decades of observations is considered lengthy enough to offset any variations you would expect from one year to the next. However, with so many weather extremes in recent years, enhanced by human-caused climate change, NOAA is serving up a modified version of its climate normals beginning later this year.
For the first time ever, NOAA will include 15-year normals to better represent a climatology period closer to today.
The new NOAA normals will be available to the public on May 4 and can be accessed on the NOAA National Centers for Environmental Information’s web page