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Southeast Temperature Trends (1901-2005)

Research suggests that the temperature of the southeastern United States has been decreasing over the past 100 years. The Southeast is distinct from other regions of the United States that do show distinct warming. Cooling in the Southeast, however, is not necessarily due to recent temperature trends. Rather, the large scale cooling is readily apparent when looking at the extended period of record. Temperatures in the early 1900s were generally cool then warmed between the 1920s and the 1940s. Starting in the 1950s, temperatures decreased until the 1970s when a general increase in temperature began. Because of the warming in the 1920s through 1940s is greater than the warming after 1970, the overall trend of the century is a cooling trend. Research is underway to identify further the general changes in temperature during the last three decades. It should be noted that not every weather station showed these trends for the past 100 years. Patterns will be seen within the study region (i.e., Georgia, North Carolina, and South Carolina) that differ quite significantly from the general temperature trends of other portions of the Southeast.

Minimum Temperature

Minimum temperature trends since 1901 in the study area best mirror the more general temperature patterns for the Southeast, albeit with some seasonal variation to these patterns. In all seasons, cooling occurs in the southern part of the study region and some warming occurs in the northern portion.

(map) Spring shows the clearest temperature signals: cooling to the south and warming to the north, with the northern border of South Carolina approximating the border between the temperature trends. The southern portion of the study region has also cooled more than the northern portion has warmed.

(map) Summer shows a warming towards the north, and a cooling towards the southern portion of the study area. As with the observed Spring pattern, there is some indication of isolated warming in the south and cooling in the north.

(map) Fall also brings a warming towards the north and a cooling towards the south in the study region. There are a few stations with opposing trends intermixed within the dominant pattern.

(map) In winter there is a distinct trend of lower minimum temperatures across the entire study area. There is no longer as clear of a pattern of warming in the northern portion as seen during the other three seasons. Some isolated stations show a warming trend.

(map) The annual pattern of minimum temperature resembles those of the seasons. The amount of cooling that has occurred over the last century is greater in the south than the warming that occurred in the north. As with four individual seasons, some isolated stations indicate warming in the south and cooling in the north.

Maximum Temperature

Unlike the minimum temperature change pattern, changes in the region's maximum temperature from 1901 to 2005 do not have a distinct pattern. Stations that show warming trends are intermixed with stations that have cooling trends in all seasons. One station, Highlands, NC, with more than a 6.5° F. decrease in maximum temperature, sits adjacent to other stations that indicate a fall warming trend. Therefore it is difficult to make a definitive conclusion on the spatial patterns of seasonal and annual trends in maximum temperature.

(map) There are slightly more stations with a warming trend than those with a cooling trend, and the magnitude of the warming is generally greater than the magnitude of cooling.

(map) The magnitudes of cooling in summer are generally greater than the magnitudes of warming.

(map) The warming and cooling trends are intermixed without a clear pattern, and the magnitudes of the changes in temperature do not indicate either warming or cooling to be predominant.

(map) In winter, more stations exhibit a warming trend than a cooling trend, and the magnitude of the warming is generally greater than the magnitude of the cooling.

(map) The warming and cooling trends were intermixed without a clear pattern, and the magnitudes of the changes in temperature do not indicate warming or cooling to be more prevalent.

An examination of the temporal changes in temperature does not provide much clarification as to any trends in temperature. In some instances, stations possess the general trends in temperature previously mentioned for the greater Southeast: temperatures in the early 1900s were generally cool, with a warm up in the 1920s to the 1940s. From the 1950s until the 1970s maximum temperatures decreased. Since the 1970s, temperatures have increased; however, the relative importance of each cooling or warming period tends to vary. For example, sometimes the temperatures in the 1920s to the 1940s are higher than in the last few decades, producing an overall cooling trend, and sometimes that pattern is reversed. In other cases, the changes in temperature for some stations differ substantially from that mentioned for the Southeast. Just as there were no coherent spatial patterns in maximum temperature, the temporal trends also vary substantially. Perhaps one of the few universal statements that can be made is that a 105-year period of record is not the appropriate time period for which to examine changes in maximum temperature in the study region.

Mean Temperature

The spatial patterns of mean temperature from 1901 to 2005 are similar to the patterns in minimum temperature albeit with the exception of winter.

(map) Spring shows the clearest pattern: cooling to the south and warming to the north roughly divided by the North Carolina-South Carolina border. The magnitudes of the warming and cooling are approximately similar.

(map) Summer also shows a cooling to the south and warming to the north. Stations that showed a warming or a cooling trend are more intermixed than in spring.

(map) Fall shows cooling to the south and warming to the north. Stations that showed a warming or a cooling trend are more intermixed than in spring.

(map) The map of mean winter temperatures show no distinct cooling (warming) in the south (north).

(map) The mean annual temperature shows cooling in the south and warming in the north with the overall pattern in mean temperature slightly less pronounced than annual minimum temperature.

Continuing Temperature-Related Research

The research to date shows some general temperature trends for the study region, although they are both seasonably dependent and dependent upon the use of maximum, minimum, or mean temperature data sets. Particularly with regard to maximum temperature, issues arise as to the utility of using the entire 105-year period of record to study temperature trends. With the possibility that humans are modifying the climate, it may be more useful to examine more recent trends in temperature. The United Nations Inter-Governmental Panel on Climate Change (IPCC) claims that an anthropogenic influence on the climate first appeared in 1979. It may therefore be more appropriate to examine temperature trends from 1979 to the present. This could reveal more accurate changes in temperature over the past few decades in the study region that could be due to human influence. Preliminary results suggest that minimum and mean temperatures have increased throughout the study region in the past three decades and therefore the Southeast may not be cooling or warming differently than the rest of the country, as has been suggested in the scientific literature. Present research is being focused to clarify temperature trends since 1979 to determine whether an anthropogenic signal exists in the temperature record.

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