Georgia, like much of the southeastern United States, is one of the few regions globally that has not exhibited an overall warming trend over the 20th century. However, under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century, including increases in heat wave intensity and decreases in cold wave intensity.
Higher temperatures will increase the rate of loss of soil moisture during dry spells, which could lead to more intense droughts and increased competition for the state’s water resources.
Global sea level has risen by about 8 inches since 1880 and is projected to rise another 1 to 4 feet by 2100. Sea level rise will increase the frequency, extent, and severity of coastal flooding, a grave risk to developments along Georgia’s coastline.
Georgia’s climate is characterized by long, hot, humid summers and short, usually mild winters, due to its latitude and close proximity to the warm waters of the Gulf of Mexico and the Atlantic Ocean. Georgia is the largest state in land area east of the Mississippi River and includes a wide range of geographic features. Elevation ranges from sea level along the coast to over 4,700 feet in the Blue Ridge Mountains in the northeast. Temperature varies substantially across the state. Inland cities, such as Macon and Columbus, experience very high summertime temperatures, with an average of 20 days per year exceeding 95°F. By contrast, Atlanta only averages seven such days per year, while areas in the Appalachian Mountains average less than one. The occurrence of very warm nights (minimum temperature above 75°F) also varies across Georgia. The Appalachian Mountains rarely experience such nights, while Atlanta averages 4 per year and Brunswick, located along the southeastern coastline of the state, experiences more than 30 annually.
Georgia, like much of the southeastern United States, is in one of the few regions globally that has not exhibited an overall warming trend in surface temperatures over the 20th century (Figure 1) while the United States as a whole has warmed by about 1.5°F. Temperatures in Georgia were highest in the 1920s and 1930s, followed by a cooling of almost 2°F by the 1960s. Temperatures have risen since that cool period by nearly 2°F such that the most recent one to two decades have been near the levels of the 1930s. The rest of the United States also cooled from the 1930s into the 1960s, but not nearly as much as the southeast U.S. including Georgia. Potential causes for this difference in warming rates have been the subject of research, but this phenomenon has not been fully explained.
Extreme high temperatures have exhibited much variability since the beginning of the 21st century. The state experienced many extremely hot days (maximum temperature above 100°F) during the late 1920s, early 1930s, and the early 1950s. This was followed by a period of few hot days in the 1960s and 1970s. The most recent decade has experienced below average numbers of such days (Figure 2a). The number of both days below freezing (maximum temperature below 32°F) and very warm nights (minimum temperature above 75°F) has also displayed similar variability over the past century (Figures 2b and 3). Despite the lack of a warming trend, the state has recently experienced several warm years. The year 2012 was the third hottest in the state’s history, with a particularly scorching June. On June 29, Athens set an all-time high temperature record of 109°F and the following day, Atlanta set a record of 106°F.
The state’s climate is favorable for a wide variety of agricultural crops; however, untimely cold spells can have devastating consequences. Freezing temperatures from April 6 to 9, 2007, after a very warm March, had severe impacts on the agricultural industry. The blueberry, peach, and pecan crops were most affected, with losses of $64.9 million, $28.1 million, and $26.9 million, respectively. Overall, the freezing temperatures resulted in more than $350 million in losses.
Georgia receives frequent precipitation throughout the year, ranging from upwards of 80 inches in the mountainous northeastern corner of the state to around 45 inches in the eastern and central portions. Statewide average precipitation has ranged from a low of 31.06 inches in 1954 to a high of 70.46 inches in 1964. The driest multi-year periods were in the early 1930s, and 1950s, and the late 1980s. The wettest multi-year periods were in the late 1940s, and the early 1960s and 1990s (Figure 4). The driest 5-yr period on record was 1954–1958 (averaging 44.88 inches per year) and the wettest was 1944–1948 (averaging 55.36 inches per year). Although Georgia has generally experienced below average precipitation since 2000, 2013 was the fourth wettest year in the state, with a statewide average of 63.49 inches. Snowfall is generally light in the state; even in the northern mountains, total annual snowfall only averages 5 inches.
The Bermuda High, a semi-permanent high-pressure system off the Atlantic Coast, plays an important role in the summer climate of the state. Typically, the Bermuda High draws moisture northward or westward from the Atlantic Ocean and the Gulf of Mexico, causing warm and moist summers with frequent thunderstorms in the afternoons and evenings. Daily and weekly variations in the positioning of the Bermuda High can have a strong influence on precipitation patterns. When the Bermuda High extends westward into the southeastern United States hot and dry weather occurs, which can result in heat waves and drought. In 2007, as the result of a strong Bermuda High over the Southeast and a strengthening La Niña, the state experienced its third driest year on record. This very dry year, compounded by low precipitation in the preceding year of 2006 (the state’s fifth driest year), led to one of worst droughts in Georgia’s history. By the end of August, most of the state was in severe or extreme drought.
Thunderstorms are common in Georgia, particularly in the spring and summer months, and often bring heavy rains, which can cause severe flooding (Figures 2c and 2d). From September 16 to 22, 2009, heavy rains caused severe flooding in North Georgia and the Atlanta area. Over this one-week period, some portions of the state received more than 15 inches of rain, with the Chattahoochee River reaching 100-year flood levels and the Sweetwater Creek Basin reaching 500-year flood levels. Seventeen counties were declared federal disaster areas and damages from the flooding exceeded $500 million. Tornadoes are another hazard of these thunderstorms. On March 14, 2008, a tornado struck downtown Atlanta, causing over $150 million in damages and one death. The following day, this storm system went on to cause multiple tornadoes across the state, including an EF3 tornado in northwestern Georgia, which killed two people. Only eight EF4 tornadoes have occurred in Georgia since 1950. One such tornado hit Catoosa County on the evening of April 27, 2011 as part of the historic April 27–28, 2011 super outbreak.
Although Georgia rarely experiences direct landfall of hurricanes, tropical storm system remnants can bring heavy rains and strong winds to the state. In 1994, Tropical Storm Alberto passed over the state, resulting in significant rain totals. The storm dropped more than 27 inches of precipitation on Americus in the southwestern part of the state—21 of those inches fell during a 24-hour period, setting a new state record. Alberto caused significant flooding, particularly along the Flint and Ocmulgee Rivers, and these floods caused extensive agricultural losses and 33 deaths. In September 2004, precipitation from the remnants of three hurricanes—Frances, Ivan, and Jeanne—resulted in Georgia’s wettest September on record and significant flooding across the state. In 1995, Hurricane Opal brought a prolonged period of strong winds to the state. There were several hours of sustained winds greater than 40 mph in Atlanta and a gust of 69 mph recorded at Dobbins Air Force Base in Marietta. Some power outages lasted more than a week, and more than 4,000 trees fell within the city of Atlanta, damaging power lines, homes, and automobiles and injuring more than half a dozen people. Many state and U.S. highways shut down due to fallen trees and power poles.
Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century (Figure 1). Even under a pathway of lower greenhouse gas emissions, average annual temperatures are projected to most likely exceed historical record levels by the middle of the 21st century. However, there is a large range of temperature increases under both pathways, and under the lower pathway, a few projections are only slightly warmer than historical records. Heat waves are projected to increase in intensity in this region, which already experiences hot and humid conditions. Extreme heat is of particular concern for Atlanta and other urban areas where the urban heat island effect raises summer temperatures. High temperatures, combined with high humidity, can create dangerous heat index values.
Precipitation projections for Georgia are uncertain (Figure 5). Even if average annual precipitation remains constant, higher temperatures will increase evaporation rates and decrease soil moisture during dry spells, leading to greater drought intensity. This could increase competition for limited water resources, which currently support large population centers in multiple states, such as the Apalachicola-Chattahoochee-Flint River Basin.
Increasing temperatures raise concerns regarding sea level rise in coastal areas. Since 1880, global sea level has risen by about 8 inches. It is projected to rise another 1 to 4 feet by 2100 as a result of both past and future greenhouse gas emissions from human activities (Figure 6). Sea level rise has caused an increase in tidal floods associated with nuisance-level impacts. Nuisance floods are events in which water levels exceed the local threshold (set by NOAA’s National Weather Service) for minor impacts. These events can damage infrastructure, cause road closures, and overwhelm storm drains. As sea level has risen along the Georgia coastline, the number of tidal flood days (all days exceeding the nuisance level threshold) has also increased, with the greatest number occurring in 2013 and 2015 (Figure 7). Georgia is at extreme risk for sea level rise due to its low elevation along the coast. Continued sea level rise will present major challenges to Georgia’s existing coastal water management system and could cause extensive economic damage through ecosystem damage and losses in property, tourism, and agriculture.