The Impact of Climate Change on South Carolina
WHAT CONTROLS SOUTH CAROLINA'S CLIMATE?
Several factors control South Carolina's climate. Most important are the state's location in the northern mid-latitudes and its proximity to the Atlantic Ocean and Appalachian Mountains. Such a location means that the amount of solar radiation received (and hence the temperature) will vary during the year to bring all four seasons to most of the state. During the summer, when the sun is most directly overhead, the state receives intense solar radiation allowing afternoon temperature to reach the 90's.
The state's geographic position on the eastern coast of a large continent is also important because land and water heat up and cool off at different rates. Not only does this heating differential affect the immediate coastal region, providing cooling sea breezes in the summer, but it influences the way pressure and wind systems affect the state.
During the summer, South Carolina's weather patterns are dominated by a maritime tropical air mass known as the Bermuda high. Passing over the land, which has heated up more quickly than the ocean, it becomes unstable. This pattern results in the formation of afternoon and evening thunderstorms.
Although the prevailing winds in North America are from the west, the Bermuda high frequently stalls off the coast in the summer, blocking the cooler, drier continental air masses that would provide relief from the hot, sultry weather. As the summer ends, the Bermuda high shifts slightly southward allowing the cooler air to penetrate. The Blue Ridge mountains to the west, however, divert some of this cooler air and protect the state from the full brunt of these cold fronts. Even in the winter days are generally mild, with southern winds often bringing warm maritime air. Rainfall in winter is generally caused by the movement of these warm and cold fronts.
WHAT IS SOUTH CAROLINA'S CURRENT CLIMATE LIKE?
South Carolina's climate is classified as humid sub-tropical; that is, temperatures vary seasonally, with summers generally hot and sultry while winters are mild, and precipitation is ample and fairly well distributed throughout the year. Although March and July are usually the wettest months of the year, there is no real dry season. In eastern South Carolina, however, winter precipitation is greater than summer precipitation. Statewide, minimum precipitation is received in October and November. During summer and early fall of most years, the state receives the effects of one or more tropical storms or hurricanes.
For the past 97 years, volunteer and professional weather observers have documented temperature and precipitation across South Carolina. Since 1895, the average annual temperature and total annual temperature and total annual precipitation have experienced small changes. Since 1957, however, the climate of the state is characterized by warmer and drier conditions. According to recent observations (1957-1991), the annual average temperature increased by nearly 1 degree F when compared to the average. The largest temperature increase resulted during the 1980's from warmer than average wintertime temperatures. Precipitation decreased six percent or 3.2 inches primarily due to lower than average springtime rainfall. Thus, the current trend in South Carolina's climate resulted in warmer and drier conditions.
WHY ARE WE WORRIED ABOUT CLIMATE CHANGE?
We are worried because even small changes in the climate can make remarkable differences in our environment. The current threat of warming is especially worrisome because it suggests temperatures will change both more and faster than normal. Some scenarios predict temperature increases of up to 3 degrees F. Changes comparable in magnitude to this have generally taken place over thousands of years: this warming could occur over the next century.
Scientists are beginning to document that we may have changed the atmosphere so much that regional and global climate changes will be enhanced. The existence of climate change resulting from the greenhouse effect isn't questioned: the earth would be about 60 degrees cooler and would not be a suitable home for us if it did not exist. First proposed by the French scientist Fourier in 1824, the term refers simply to the capacity of certain gases to allow shortwave solar radiation to reach the earth's surface but then absorb and trap this same energy as the earth radiates it back as longwave energy. This trapped radiation increases the air's temperature. Water vapor is responsible for most of this warming, but carbon dioxide (CO2) also plays an important role in warming the earth's atmosphere.
Indeed, ice-cores taken from the Antartic and Greenland show that temperature and CO2 levels have increased and decreased in tandem over the last 160,000 years. Many climatologists believe that because CO2-levels have climbed 25 percent since the industrial revolution began, global temperatures must also rise. This increase in CO2 is attributed largely to human activities since 1945. The burning of fossil fuels adds 5.6 billion tons of carbon to the atmosphere each year; deforestation contributed another .4 to 2.5 billion tons.
Carbon dioxide, though, isn't the only greenhouse gas scientists are concerned about. The atmospheric concentrations of methane (CH4), chlorofluorocarbons (CFC's), and nitrous oxide, which are even more effective than CO2 in trapping heat in the atmosphere, are also growing. If we continue with business as usual, an effective doubling (including the effects of CH4, CFC's, and Noxs) of pre-industrial CO2-levels will take place by the year 2030. The World Resources Institute claims that even if future emissions were to cease, out past emissions have already guaranteed we will face a warmer world. Most of this warming, however, could be delayed by increased cloudiness and may occur just prior to the onset of the next glacial period in the Earth's history.
How Might South Carolina's Climate Change?
To determine how the climate will respond to increases CO2 levels, climatologists use general circulation models (GCMs). GCMs express mathematically the large-scale dynamic and thermodynamic processes of the atmosphere and their associated feedbacks. While such models can't replicate reality, they can reveal what we might expect to happen if certain components of the earth's climate system change. When researchers double the carbon dioxide levels, the models indicate global temperature will increase from 2 to 4 degrees F.
The Goddard Institute of Space Sciences (GISS), the geophysical and Fluid Dynamics Lab (GFDL) of Princeton, and Oregon State University (OSU) have designed some of the more prominent general circulation models. While these GCMs are currently the tools used for estimating climate change, they are not problem-free. There are problems with the models themselves. Certain important variables (like clouds) are too small to be included individually in the models and must be represented collectively, i.e. parameterized. Differences in how models parameterize these variables makes a difference in the estimates of climate change produced. When the designers of one model recalculate its parameterization of clouds, the estimated temperature increase was more than halved, dropping from 9.9 to 3.4 degrees F.
Other uncertainties arise because we don't fully understand the feedback mechanisms at work in the climate. The long-term response of vegetation and the deep oceans, which are treated crudely if at all in GCMs, may dampen or amplify anticipated changes. Or these feedbacks may affect the rate of change, acting to accelerate or retard it.
General circulation models also present problems when used to study climate impacts. Because GCMs are attempts to describe global processes of the atmosphere, they don't translate easily into regional change scenarios. It is the regional patterns of changes, though, that will determine how the impacts are felt. Policymakers must be cautious then in using GCM's to formulate policy across the state.
Even with these caveats and uncertainties, GCM's when combined with the historical climate record is the best tool we have for predicting future climatic change. The current models suggest that if the amount of CO2 in the atmosphere should double, temperatures will increase from 2 to 4 degrees F. But the increased temperatures won't be the only change we can expect. Although we commonly speak of climate change in terms of temperature, temperature is only one part of this change. Temperature drives other climate features. Wind systems, precipitation patterns, and ocean circulation arise from the atmospheric energy balance. Temperature increases will change these patterns, too. Scientists also believe that this change might bring about the increase in the number of extreme weather events, especially in the mid-latitudes. Hurricanes, droughts, and the number of 100 degree days might all become more frequent in a warmer world, but there is no evidence to confirm this belief.
The U.S. Environmental Protection Agency has used three models (GISS, GFDL, and OSU) to produce a range of climate change scenarios for the Southeastern region of the United States. Although they differ in particulars, the three GCMs agree in their forecasts for temperature in the Southeast—they suggest the region could experience an annual warming. The GFDL model estimates a higher winter increase than the other two, but all suggest that both summer and winder temperatures will increase.
Differences among the models become more apparent when the expected change in precipitation is examined. Averaged over the year, the GISS and OSU models see a slight increase in precipitation, while the GFDL model see a decrease. Most important is the disagreement over summer rainfall patterns: the GISS model predicts large increases, the OSU model a slight increase, and the GFDL model a dramatic decrease. The disagreements here are important. It may well be that the availability and reliability of water supply will be more important than temperature changes in determining the impact of climatic change of societies.
WHAT MIGHT THESE CHANGES MEAN TO SOUTH CAROLINA?
These are important reasons to believe that the changes outlined above would subject South Carolina to a disproportionate share of the physical aspects of climate change impacts. As a state we are heavily dependent on our natural resources: tourism, forestry, recreation, agriculture, and the fishing industry are key sectors in the state's economy. Forestry and tourism are most vulnerable to the rising sea levels, hotter summers, and changes in precipitation that global warming scenarios predict.
Here are some changes we might expect:
Agriculture and the fishing industry – While experts estimate that US agricultural production will be adequate for domestic needs even under the most extreme scenario, they do expect major regional changes in the production and quality of food commodities. Production is generally seen as shifting northward, with crops in the Southeast particularly vulnerable.
Productivity could change -- Although warmer temperatures may lead to increase yields in some parts of the country, South Carolina already has a high baseline temperature. Adding to it is likely to increase the moisture and heat-stress crops are subject to. The wettest scenario doesn't offset crops' increase water needs, and the dry one suggests yield could decrease by nearly 80 percent. Even the direct positive effects on photosynthesis of a CO2-enriched atmosphere can not in such cases make-up for the indirect effects of moisture-stress resulting from climatic change.
Need for irrigation may increase – Under the wet GISS scenario it is still estimated that the Southeast will require increase irrigation. Already irrigation land will require more water, and more land will require irrigation.
Crop mix may change – With warmer temperatures, crops like corn would cease to be profitable in the Southeast, while heat-tolerant crops like cotton could make a come back. Adjustments might also be made in varieties planted: peach farmers in Saluda, Lexington, Edgefield, and Aiken Counties might find themselves favoring varieties like May Gold and Early Amber over their present Red Globe and Jefferson trees to ensure the necessary dormancy period is achieved.
Disease and pest vulnerability might increase – Warmer conditions may accelerate the life cycles of insect pests, leading to attacks on plants at earlier and more susceptible stages of growth. The range of some Gulf Coast pests could also shift northwards if winters became less severe.
Cultivated acreage could decrease – Because many South Carolina farms are already marginal enterprises, farmers may not be able to compete in a changed environment. The amount of land under cultivation could decrease.
Fish and shellfish populations could be reduced – Both increased water temperatures and changes in the salinity of habitats could reduce the population of species profitable to the state's fishing industry.
Forestry – With over 60 percent of the state classified as forested, it is not surprising that forestry and forest-related industry is a key sector in South Carolina's economy. Only tourism brings more money into the state and, as sites for fishing, hunting, hiking, and camping , forests contribute to that sector, too. The economic benefits forests bring not just important to the state, they are important to individuals in the state: almost two-thirds of the forests remain in private, non-industrial hands. We have a right to be alarmed then when studies indicate climate change could cause significant changes in South Carolina's forests.
- Dieback of forests in 30 to 80 years. Even modest warming could cause significant changes, but a CO2-induced warming poses the additional threat of occurring so quickly that forests would not be able to adjust in time.
- Loss of species. Southern hardwoods (black gum, laurel oak, and elm) might replace loblolly pines as the dominant species.
- Conversion of Forest to Grasslands. The drier scenarios suggest that sections of the Southeast might not support forests at all. Abandoned farms that have traditionally reverted to forest might now remain in grass.
- Increased vulnerability to pests and disease. Not only is the range of pests likely to increase, but climate-stressed stands are more susceptible to attack by disease, pests, and fire.
Water Resources
Exactly how water resources will be affected by climate change is difficult to ascertain. Not only do the GCMs vary widely in how they expect precipitation (i.e. the supply of water) to change, but climate changes will also influence the demand for water.
- Water Resource availability could change. Studies indicate the regional availability and reliability of water resources may be responsible for the most dramatic effects of climate change. With warmer temperatures, demand for water is likely to increase for agriculture, energy, cooling, and recreation. It is not certain whether the supply will be able to meet the demand.
- Water quality could be affected. Regardless of precipitation changes, water quality could be affected. Drier scenarios create oxygen-starved lakes and streams; wet scenarios increase the threat of pollution from runoff.
- Risk of flooding might increase. The capacity of current drainage system to handle an increase in the frequency of large amounts of precipitation might be exceeded under some scenarios.
Energy
Our demand for electricity is rather sensitive to the weather and to industrial growth. Changes in the weather patterns mean changes in energy consumption. Higher temperatures would mean:
- An increase demand for air conditioning. Higher summertime temperatures would mean increased use of air conditioners; the cooling season would also last longer.
- Decrease in demand for heating. Warmer winters would decrease the amount of energy required for heating.
- Require an increase in electrical capacity. Higher demands for air conditioning in the summer would be partially offset by lower wintertime temperatures, affecting total consumption only moderately. But the periods could require a significant increase in South Carolina's electrical capacity.
The impact of climate change on South Carolina was produced by the S.C. Water Resources Commission (now Department of Natural Resources) – office of the State Climatology and the S.C. Governor's Office. This publication was funded by a grant from the U.S. Environmental Protection Agency. Additional copies of this publication can be obtained from:
S.C. Department of Natural Resources
Office of the State Climatology
P.O. Box 167
Columbia, South Carolina 29201
(803) 734-9100
