Heat records tumbled across the country last spring and summer as heat waves and warmer-than-normal temperatures blistered much of the U.S. As scientist Deke Arndt and meteorologist Dan Satterfield explain in this edition of Extreme Weather 101, those heat spikes are likely to become more commonplace as greenhouse gases heat the planet.More
The heat records just keep piling up. Last month was the hottest April on record, according to both NASA and the National Oceanic and Atmospheric Administration.
In NOAA’s annals, April was also the 12th consecutive month to break such a record — the longest such streak in 137 years of record keeping. And of the 15 months that have been the most anomalously warm in that period, 13 have occurred since February 2015.
With a global year-to-date temperature that is 2.05°F (1.14°C) above the 20th century average by NOAA’s reckoning — far warmer than this point last year — 2016 is poised to become the warmest year on record.
As these records pile up, they affect long-term temperature averages, or what can be confusingly referred to as “normal.”
From a meteorological standpoint, normal is the 30-year average temperature for a particular location. NOAA calculates a new normal at the end of each decade, and it is the standard for most meteorological applications, like when your local forecaster tells you how the daily temperature compares to normal.
The current normals are based on the average temperatures from 1981 to 2010. The next normals will be based on the period from 1991 to 2020.
As the planet has warmed from the increase in greenhouse gases in the atmosphere, those normals have have mostly risen. In an overwhelming majority of sites across the country, the current normals are higher than those from 30 years ago (1951-1980).
While NOAA has been producing normals since the 1921-1950 period, the meteorological database becomes more complete beginning in the 1951-80 period.
Climate Central expanded on this idea, calculating a 30-year average each year from 1980 to 2015 for the 135 sites in its Climate Matters network. For example, the normal temperature for 1980 in this analysis was based on the average temperature from 1951-1980, and the 2015 normal is the average from 1986-2015.
At 97 percent of the sites studied by Climate Central, the new normal is warmer than 35 years ago. Thinking in more human terms about how we acclimate to temperatures during our lifetimes, days that seem moderately hot to younger generations may seem exceptionally hot to their parents or grandparents.
The shift in these normals has already become apparent in the longer growing season for most of the country, with the average last freeze of the season coming earlier in the spring and the first freeze happening later in the fall. Some plant and animal species are migrating northward or upward in elevation as a result, meaning a variety of pests and weeds are now found in places previously too cold for them to live.
While the changes in a fraction of a degree may seem small, it has a large impact on the frequency of extreme temperatures, with a substantial increase in extreme heat and a substantial decrease in extreme cold.
For most of the country, winters have been warming more rapidly than summers. Although less extreme cold sounds appealing, the future effects of blistering summer heat are expected to outweigh the benefits of milder winters. More extreme heat will increase the threat of heat-related illness such as heat stroke. In addition, this expansion in very hot days will stress the nation’s aging electric grid, driving up cooling costs as air conditioners will likely be used more frequently.
Even in a warming world, there will still be cold spells, but they will be less intense and happen less frequently.
Regions of the country with colder climates, such as the Twin Cities, have seen some of the most dramatic decreases in extreme cold.
Given the number and intensity of heat records being set since 2010, expect the next round of NOAA normals (1991-2020) to be warmer still.