Temperature Trends in the United States


Tere are a few basic aspects we need to understand about the dynamics of temperature across North America. First, temperatures are not changing uniformly across North America as shown in Figure 1. We would expect regional differences in temperature and the observed trends in the data show that to be a reality; however, it may be surprising to everyone that in areas of the U.S., the rate is three-to-four degrees Fahrenheit per century and in other areas, e.g., northwest and southeast, the temperature trends are very small. Regional variability is expected and when the data are shown for the U.S., the amount of variation among regions becomes evident.


In an earlier Turf News article, the reason for the increase in temperature as the levels of greenhouse gases in the atmosphere increase, showed how the atmosphere is able to trap more energy causing the temperatures to increase. Te analogy is how quickly a car gets hot during the summer because the sunshine penetrates the glass, but the warm air that is caused by the sunshine is not able to escape, thus increasing the temperature. In fact, nine of the ten deadliest worldwide heat waves have occurred since 2000, just a fact that shows how much we have changed temperatures around the world and the potential impact on humans and all biological systems.


Figure 2. Trends in the maximum temperature for the summer period (July-September) for Georgia. Downloaded from NOAA National Centers for Environmental Information, Climate at a Glance: National Time Series, published September 2019, retrieved on September 17, 2019 from https://www.ncdc.noaa.gov/cag/


Figure 3. Trends in the maximum temperature for the summer period (July-September) for Iowa. Downloaded from NOAA National Centers for Environmental Information, Climate at a Glance: National Time Series, published September 2019, retrieved on September 17, 2019 from https://www. ncdc.noaa.gov/cag/


Differences between Maximum and Minimum Temperature Trends An important part of the changing temperature regime is the unequal pattern in the temperature changes. Te expectation when we talk about temperature increases is that both the maximum and minimum temperatures are increasing together. Changing temperatures show a trend in which the minimum temperatures are increasing more rapidly than the maximum temperatures. In reality, our temperatures are increasing because the maximum and minimum temperatures are showing less difference. Data on the average, maximum, and minimum temperatures are available for every state from https://www.ncdc.noaa.gov/cag/statewide/time-series. Shown here are examples for Georgia and Iowa (Summer, July-September). Tis site will allow you to download information for your specific state or county level so that you can examine a particular site of interest. It is recommended you use either Chrome or Firefox for the best results in searching and downloading data. In both Georgia and Iowa, summer maximum temperatures are showing a decline (Figures 2 and 3), i.e. the maximums actually are not as hot.


TPI Turf News November/December 2019 103


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