Minimum average temperature is provided as it best reflects the rise in temperature over the period of record. Temperature plots exhibit interannual variability, however, the long term trend across the region shows an increasing annual trend. Additional parameters such as average temperature are also available and can be found here at https://www.ncdc.noaa.gov/cag/county/time-series.
Source: NOAA, National Centers for Environmental Information, 2020
The graphic shows the projected average number of days per year with maximum temperatures above 95°F for 2041– 2070 compared to 1971–2000, assuming emissions continue to increase.
Projected Number of Warm Nights
The maps show the projected number of warm nights (nights with minimum temperatures above 75°F) per year in the Southeast for mid-21st century (left: 2036–2065) and the late 21st century (right: 2070–2099) under a higher greenhouse gas emissions scenario (top row: RCP8.5) and a lower scenario (bottom row: RCP4.5).
These warm nights currently occur only a few times per year across most of the region, but are expected to become common events across much of the Southeast under a higher emission scenario. Increases in the number of warm nights adversely affect agriculture and reduce the ability of some people to recover from high daytime temperatures. With more heat waves expected, there will likely be a higher risk for more heat-related illness and deaths.
Historical and Projected Heat Index
Heat Index is a function of both temperature and humidity — it is a measure of how hot it really feels when relative humidity is factored in with the actual air temperature. The tables show the Heat Index by county historically (1971-2000), by midcentury (2036-2065), and by late century (2070-2099). Data for each county was derived from the Union of Concerned Scientist Killer Heat in the U.S. Report, where future values were computed as the average of 18 climate models. The term “Off the Charts” used in the tables refers to levels of exposure to heat index beyond approximately 135℉, which is presumed extremely dangerous for all people and likely to result in heat-related illness or even death.
To find the Heat Index temperature, look at the Heat Index Chart above or check this Heat Index Calculator. As an example, if the air temperature is 88°F and the relative humidity is 80%, the heat index–how hot it feels–is 106°F. The orange area without numbers indicates extreme danger. The National Weather Service will initiate alert procedures when the Heat Index is expected to exceed 105°-110°F (depending on local climate) for at least 2 consecutive days.
Caveats to Heat Index Data:
When applying these results to any location or population, a number of limitations should be considered:
- The heat index is based on physiological assumptions that assess the impacts of hot and humid weather on humans. Variations in clothing thickness, height, weight, age, health, and physical activity are not accounted for in the heat index calculation. The index also does not include wind speed, cloudiness, shade levels, or any other factors, although those are known to affect heat-related impacts.
- The climate model data used for this analysis were created using the Multivariate Adaptive Constructed Analogs (MACA) method. Different climate downscaling techniques could produce different results.
- The results reported are averages over 30-year periods. Because substantial warming is projected to occur over the course of those periods, the number of extreme heat index days is likely to be lower than the reported averages at the beginning of each 30-year period and higher at the end.
- The data reported here do not capture the unique characteristics of urban areas and the associated urban heat island effect, nor do the projections consider future urban development or land-cover changes that would influence future climate extremes.
Source: Killer Heat in the United States: Climate Choices and the Future of Dangerously Hot Days. Union of Concerned Scientists.