Photo by Clara Ferguson-Brown
Key Message 1
Mean annual temperature has increased by under 1°F since the beginning of the 20th century. Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century.
Key Message 2
The number of landfalling hurricanes in North Carolina is highly variable from year to year. Hurricane-associated storm intensity and rainfall rates are projected to increase as the climate warms.
Key Message 3
A large portion of North Carolina’s coastline is extremely vulnerable to projected sea level rise due to its low elevation and subsidence of land in the northern part of the Coastal Plain. Global sea level is projected to rise by 1 to 4 feet by the end of the 21st century.
North Carolina has a humid climate with very warm summers and moderately cold winters. The climate exhibits substantial regional variation due to the state’s diverse geographic elements, which include the Appalachian Mountains in the west, the Piedmont Plateau in the central region, and the Coastal Plain to the east. Elevations in the state range from sea level along the Atlantic Coast to over 6000 feet in the western mountains (the largest elevation range of any state east of the Mississippi River). Average annual temperatures in the state vary more than 20°F from the highest elevations to the lowest points on the coast. Winter temperatures are moderated somewhat by the Appalachian Mountains which partially block cold air coming from the Midwest.
Mean annual temperature has increased by under 1°F in North Carolina since 1900, less than in northern and western portions of the United States. North Carolina is part of a larger region of the southeastern U.S., which has exhibited little overall warming in surface temperatures over the 20th century. During the first half of the 20th century, many years were greater than the long-term average, followed by a cool period in the 1960s and 1970s. Since that time, temperatures have steadily increased, with temperatures being consistently above normal since the late 1990s (Figure 1). Average winter temperatures have been above average since 1990, but not as warm as the early 1930s and early 1950s (Figure 2). However, average summer temperatures have been the warmest on record over the last decade (Figure 2). Although North Carolina has not experienced an increase in the frequency of very hot days (days with maximum temperature greater than 95°F) (Figure 3a), the most recent 5-year period (2010–2014) has seen the largest number of very warm nights (days with minimum temperature greater than 75°F) in the historical record (Figure 4).
Observed Number of Very Warm Nights
Statewide average annual precipitation has ranged from a low of 34.74 inches in 2007 to a high of 63.17 inches in 2003. The driest multi-year periods were in the early 1930s and early 1950s, and the wettest in the late 1900s, early 1940s, 1970s, and late 1990s (Figure 3b). The driest 5-year period was 1930–1934 with an average annual precipitation of 44.39 inches and the wettest was 1971–1975 with an average of 54.36 inches per year. There is no overall trend in annual precipitation. Precipitation totals are generally highest in the summer, with a peak in July. Southwestern North Carolina is one of the wettest locations in the Southeast, receiving more than 90 inches of precipitation annually in a few locations. The number of heavy rain events (days with rainfall exceeding 3 inches) was highest in the late 1990s but has been near average since then. There is no overall trend. The state averages around 5 inches of snowfall annually, although the higher elevations of the Appalachian Mountains can receive up to 100 inches. Snow and ice storms have the potential to cause significant damage. Some of these storms are the result of “cold air damming” which occurs when cold air becomes trapped against the Appalachian Mountains by a layer of less dense warm air above it. A strong cold air damming event took place on February 12–13, 2014, causing a severe winter storm. Large portions of the state received between 5 and 10 inches of snow and some areas received as much as half an inch of freezing rain.
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 Gulf of Mexico, causing warm and moist summers with frequent thundershowers 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, warmer and drier than normal weather occurs, which can culminate 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 driest year in history. By the end of August, most of the state was in severe drought.
North Carolina’s location along the Atlantic Coast makes the state vulnerable to tropical storm and hurricanes. A storm reaches the state at hurricane intensity about once every three years (Figure 3d). However, storms that reach the state at less than hurricane intensity can also have major impacts. The late 1990s and early 2000s were a notably active period of storms reaching the state at hurricane intensity (Figure 3d). In addition to damaging winds and coastal flooding from storm surges, extreme precipitation from these storms is a great hazard to the state. In 1999, Hurricane Floyd dropped 15–20 inches of rain in the eastern part of the state, which was still recovering from flooding caused by Hurricane Dennis several weeks earlier. Beginning on September 6, 2004, the remnants of Hurricane Frances dropped 6–10 inches of rain across much of western North Carolina over a three-day period. Less than two weeks later, the remnants of Hurricane Ivan struck the same area, dropping 10 inches of rain and causing hundreds of landslides in the mountains. During October 7–9, 2016, Hurricane Matthew dumped torrential rain in eastern North Carolina with many locations receiving more than 10 inches and a few locations in excess of 18 inches, causing major flooding. In addition to damage from high winds and flooding, hurricane strikes can produce tornadoes. Rainbands associated with Hurricane Frances spawned multiple tornadoes in the central and eastern portions of the state.
Severe thunderstorms are another hazard commonly experienced within the state. These occasionally spawn tornadoes. The largest such outbreak occurred on April 16, 2011, with 30 confirmed tornadoes and 24 deaths.
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 (Figure 1). Future heat waves are likely to be more intense, but cold wave intensity is projected to decrease.
Although there is no historical trend, annual precipitation is projected to increase in North Carolina (Figure 5), primarily in the winter and spring. Naturally occurring droughts are projected to be more intense because higher temperatures will increase the rate of loss of soil moisture during dry periods. Additionally, hurricane-associated storm intensity and rainfall rates are projected to increase as the climate warms.
Projected Change in Annual Precipitation
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 1–4 feet by 2100 as a result of both past and future 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 North Carolina coastline, the number of tidal flood days (all days exceeding the nuisance level threshold) has also increased, with the greatest number occurring in 2014 and 2015 at Wilmington (Figure 7). Large increases in nuisance flooding at Wilmington are projected (Figure 7). A large portion of North Carolina’s coastline is extremely vulnerable to sea level rise due to its low elevation and to geological factors that are causing sinking of the land in the northern part of the state. Sea level rise will present major challenges to North Carolina’s existing coastal water management system and may cause extensive economic damage through losses in property, tourism, and agriculture.
Past and Projected Changes in Global Sea Level
Observed and Projected Annual Number of Tidal Floods for Wilmington NC
- Kunkel, K.E, L.E. Stevens, S.E. Stevens, L. Sun, E. Janssen, D. Wuebbles, C.E. Konrad II, C.M. Fuhrman, B.D. Keim, M.C. Kruk, A. Billet, H. Needham, M. Schafer, and J.G. Dobson, 2013: Regional Climate Trends and Scenarios for the U.S. National Climate Assessment. Part 2. Climate of the Southeast U.S., NOAA Technical Report NESDIS 142-2, 94 pp. [Available online at https://www.nesdis.noaa.gov/content/technical-reports]
- Midwestern Regional Climate Center, cited 2016: “(1981-2010) Maps of gridded data long-term averages; Average Temp — North Carolina.” [Available online at http://mrcc.isws.illinois.edu/CLIMATE/]
- N.C. Coastal Resources Commission Science Panel, 2015: North Carolina sea level rise assessment report: 2015 update to the 2010 report and 2012 addendum, 43 pp. [Available online at https://ncdenr.s3.amazonaws.com/s3fs-public/Coastal%20Management/documents/PDF/Science%20Panel/2015%20NC%20SLR%20Assessment-FINAL%20REPORT%20Jan%2028%202016.pdf]
- NCSU, 1999: Hurricane Floyd, September 1999, Event Summary, National Weather Service Raleigh, North Carolina State University. [Available online at http://www4.ncsu.edu/~nwsfo/storage/cases/19990915/]
- NCSU, 2004: Hurricane Frances, September 2004, Event Summary, National Weather Service Raleigh, North Carolina State University. [Available online at http://www4.ncsu.edu/~nwsfo/storage/cases/20040908/]
- NCSU, 2004: Hurricane Ivan, September 2004, Event Summary, National Weather Service Raleigh, North Carolina State University. [Available online at http://www4.ncsu.edu/~nwsfo/storage/cases/20040917/]
- NCSU, 2011: April 16, 2011 North Carolina Tornado Outbreak, Event Summary, National Weather Service Raleigh, North Carolina State University. [Available online at http://www4.ncsu.edu/~nwsfo/storage/cases/20110416/]
- NCSU, 2014: February 12-13, 2014 winter storm, North Carolina State University. Published February 16, 2014, retrieved July 1, 2015. [Available online at http://www4.ncsu.edu/~nwsfo/storage/cases/20140213/accum.20140213.gif]
- NOAA, cited 2016: Climate at a Glance: U.S. Time Series, published October 2016, retrieved on October 18, 2016, National Oceanic and Atmospheric Administration National Centers for Environmental Information. [Available online at http://www.ncdc.noaa.gov/cag/]
- NOAA, cited 2016: Climate of North Carolina, National Oceanic and Atmospheric Administration. [Available online at https://www.ncdc.noaa.gov/climatenormals/clim60/states/Clim_NC_01.pdf]
- NOAA, cited 2016: Hurricane Floyd storm summary, Newport/Morehead, North Carolina, National Oceanic and Atmospheric Administration. [Available online at http://www.weather.gov/mhx/Sep161999EventReview]
- NOAA, cited 2016: State of the Climate: Drought for Annual 2007, published online January 2008, retrieved on December 29, 2016, National Oceanic and Atmospheric Administration National Centers for Environmental Information. [Available online at http://www.ncdc.noaa.gov/sotc/drought/200713]
- NOAA, cited 2016: State of the Climate: National Overview for February 2014, published online March 2014, retrieved on December 29, 2016, National Oceanic and Atmospheric Administration National Centers for Environmental Information. [Available online at http://www.ncdc.noaa.gov/sotc/national/201402]
- UNCA, 2014: Ten years later - Symposium explores lessons of 2004 flood from Hurricanes Frances and Ivan, News Center, University of North Carolina Asheville, published August 12, 2014, retrieved July 7, 2015. [Available online at https://news.unca.edu/articles/flood-symposium]
- USDA, cited 2016: U.S. Drought monitor CONUS, U.S. Drought Monitor Map Archive, United States Department of Agriculture. [Available online at http://droughtmonitor.unl.edu/MapsAndData/MapArchive.aspx]