Just like the census is taken every 10 years and we get all kinds of new population and demographic information. In meteorology we derive new normal temperatures and precipitation data very 10 years too. We now have a new set of weather “normals” for Charlotte. The old normals were the averages from 1971-2000 and now the new ones run from 1981-2010.
I should say I hate the word normal, since what these really are is just a 30 year average. There really isn’t anything normal about weather it’s just all averages.
So why do we update the “normals” every 10 years? Here’s why from the NCDC (National Climatic Data Center web-site).
NOAA’s computation of climate Normals is in accordance with the recommendation of the World Meteorological Organization (WMO), of which the United States is a member. While the WMO mandates each member nation to compute 30-year averages of meteorological quantities at least every 30 years (1931 – 1960, 1961 – 1990, 1991 – 2020, etc.), the WMO recommends a decadal update, in part to incorporate newer weather stations. Further, NOAA’s NCDC has a responsibility to fulfill the mandate of Congress “… to establish and record the climatic conditions of the United States.” This responsibility stems from a provision of the Organic Act of October 1, 1890, which established the Weather Bureau as a civilian agency (15 U.S.C. 311).
So how have they changed for Charlotte? Take a look at the monthly changes and notice there are some significant changes.
Old “Normals” 1971-200
New “Normals” 1981-2010
The complete spread sheet can be viewed by clicking here. I should also note these are just the monthly changes every single day will now have a new “normal” high, low, rainfall etc.… as well.
You’ll Notice that every single month had a decline in average temperature. The largest appear to be at night with our lows. The months with the biggest minimum declines were July –2.5°, September –2.6°, December –2.6° and January –2.5°. Things have gotten drier as well by almost 2”. Which would make sense since in the decade of 2000-2010 we had 2 very serious and long droughts.
So what does this say or mean?
You can’t read too much or too little into these numbers except to say that things have gotten slightly cooler in Charlotte since the last averages calculation. This is still just a snap shot in time of our climate. Our records date back to 1878 so this is just a 30 year trend right now it may change again in 10 years. This doesn’t confirm or refute any kind of climate shift globally, just a change locally in Charlotte’s average temperatures over the past 30 years.
I do think that people’s perception that it’s getting hotter is just that…. a perception. The numbers just don’t back that up. I think social, economic factors and demographics shifts in the Charlotte population over the years makes people perceive the weather differently. With so many transplants from up north living here along with the overuse of A/C people tend to believe it’s getting hotter. When in fact many people are moving from cooler climates and spending way too much time indoors in the A/C. Which I believe over sensitizes people to the heat. I also think antidotal evidence would suggest as the obesity rates increase so does the amount of people who feel hotter. Research has shown that people who spend many hours in central heating and cooling burn less calories. (Source)