Global warming stripes, a visualization technique to show the changes in global temperatures between 1850 and 2021
Global warming stripes. Developed by Dr. Ed Hawkins of the University of Reading as a visualization technique to show the changes in global temperatures between 1850 and 2021. (Image by Dr. Ed Hawkins, 2022)

Archaeological sites are found all over North Carolina. Sites may be at the bottom of the ocean or the tops of the mountains. These differing environments impact current and future site preservation.

As climates change, the environmental conditions change, and this threatens archaeological sites. These threats include temperature, precipitation, extreme weather events, ocean properties, and sea-level rise. Environmental conditions are location-dependent. Threats that impact mountain sites will not impact coastal sites in the same way. Threats that impact underwater sites will not impact land sites in the same way.

Predicting the effects of these threats is difficult. We know they are increasing with climate change, but we do not know the speed or size of their impacts. Erosion to coastal and river sites is visible, but other threats are not. This invisibility makes it difficult to study the specific impacts on site preservation. Archaeologists must consider all potential threats, visible and invisible, when assessing at-risk locations.

Expand the threats below to learn more about the impact of each on archaeological sites.

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Temperature is the measure of hotness or coldness of the air and one element of a region's climate. It changes from day to day and varies from day to night. Climate change is the long-term shift in daily weather, including average temperatures. Changing temperatures are due to natural and human-made factors and are one of the most visible threats of climate change. Average global temperatures have been increasing since the 1700s. They will increase another 1.5 degrees F by the year 2100. While this seems small, any amount of extra heat in the atmosphere will great impact.

North Carolina, USA warming stripes, showing the change in average temperatures of North Carolina since 1895.
North Carolina, USA warming stripes, showing the change in average temperatures of North Carolina since 1895. (Image by Dr. Ed Hawkins, 2022)

Increasing temperature affects many aspects of nature. Soil holds water from rain, nearby streams, and groundwater. When temperatures rise, evaporation of this water increases, drying out the soil. Dry soils lead to increased environmental damage from wind, water erosion, drought, and wildfires.

Plants and animals have adapted over time to particular environments with steady climates. As temperatures rise, these environments are moving across the landscape. Some wildlife may be resilient to these changes, but others may have to move to cooler areas. Rising temperatures will also affect wildlife population size. Temperature triggers many biological processes, including reproduction. When maturity begins occurring earlier, reproduction happens faster and lifespans become shorter. Delicate balances in plant and animal populations that sustain ecosystems become disrupted.

All of North Carolina will experience the effects of rising temperatures. Warming temperatures result in hotter days and warmer nights and increased soil evaporation. This dryness increases the likelihood of erosion, droughts, and wildfires. Plant and animal ranges will begin shifting north. Native species will begin to disappear while new species invade the drying environments. This significantly alters local communities and ecosystems.

Impacts on Archaeological Sites

Changing temperature is a threat to archaeological sites. More warmth increases evaporation, affecting artifacts and site stability. Wood and metal artifacts become brittle and crumble when too dry. Dry sites face threats from wind and water erosion and even burning, which can ruin site context and move artifacts. This irreparably damages the information archaeologists can learn from a site.

The Adam Spach House, an 18th century colonial rock home in Davidson County
The Adam Spach House, an 18th century colonial rock home in Davidson County. Today, the archaeological site shows visible evidence of a house through the rock walls. Temperature increases have allowed moss and other plant growth to overtake the visible structure at the site. (Image by NCOSA, 2021)

Many archaeological sites serve as natural habitats for native plants and wildlife, providing food and shelter. Over decades and centuries, sites reach a balance with the wildlife around them. As these native species move away due to rising temperatures, balance becomes disrupted. New species further degrade the soils around sites, making them vulnerable to wind and water erosion.

Precipitation is the falling of water to the Earth's surface. Gathering moisture in the atmosphere becomes heavy and falls back to Earth. Depending on the temperature, this moisture falls as rain, snow, or ice. As warming global temperatures increase evaporation, increase moisture leads to more frequent precipitation.

Changes in precipitation lead to rapid environmental changes. Places with increased rain are prone to flooding, both in the area of rainfall and downstream. Flooding not only damages structures but also erodes riverbanks and weakens trees. Areas with reduced precipitation are more likely to experience drought. Bodies of water like rivers and lakes rely on regular rain patterns to sustain them. With reduced rainfall, these aquatic ecosystems begin to disappear, destroying the landscape. These dry areas are at greater risk for devastating wildfires as well.

Groundwater is the greatest source of safe water for human use and vegetation. Rainwater seeps through the soil and into the bedrock that stores groundwater. As rain patterns change, groundwater reservoirs replenish at a less predictable rate. This is particularly detrimental in areas with decreased rainfall. In coastal areas, saltwater can enter these reservoirs when they are not filled with fresh water. This threatens the plant life that draws on fresh groundwater for survival.

High water levels in the Swannanoa River at the Biltmore Village in Asheville
High water levels in the Swannanoa River at the Biltmore Village in Asheville. The high river levels and associated flooding happened because of heavy rains associated with the weakening of Tropical Storm Alberto in May 2018. (Image by NC Historic Preservation Office, 2018)

Changes in precipitation will affect all North Carolinians. The most significant changes will occur in the west, where rain will increase. Extreme precipitation, events with 3 or more inches of rain, will become more frequent throughout the state. These events will occur more so during the summer months. With destabilized weather patterns and warming temperatures, droughts become more likely as well. Increased evaporation and drying soil contribute to the potential for wildfires.

Impacts on Archaeological Sites

Context, which is where an artifact is found and its association with others, is the most important information archaeologists gather from a site. Increased rainfall leads to erosion in and around archaeological sites. Erosion can move artifacts from sites and disrupt context. Things like landslides and riverbank collapses can destroy entire sections of a site. Water collecting on sites can rot organic artifacts like wood, fabric, and plant materials. Increased water and warmth encourage new plant growth and animal habitation. These activities can destabilize sites.

Water pooling in the farm fields at the Duke Homestead State Historic Site in Durham County
Water pooling in the farm fields at the Duke Homestead State Historic Site in Durham County. Water pools in areas across the field due to increased heavy precipitation events and increase precipitation days. Too much rain saturates the ground. This saturation keeps additional water from infiltrating the ground and causes it to pool on the surface. (Image by NC Office of State Archaeology, 2019)

Changing rain patterns produce more erratic cycles of wet and dry. When large quantities of water enter a site the soil and soft artifacts well. As water evaporates, the drying leaves behind cracks that destabilize the site. A dry and destabilized site is vulnerable to erosion, wildfires, and land shifting. Reduced groundwater supplies can also lead to land settling and shifting. Water evaporation often leaves behind a higher concentration of salts in the soil. Salts are detrimental to the preservation of many artifacts, particularly metal materials.

Sea level is the average height of the ocean's surface compared to the Earth's center. Over time, this level has changed due to global temperatures. Cooler temperatures promote freezing, forming glaciers and sea ice, which decrease sea level. As temperatures rise, these ice formations are melting, increasing the sea level. Oceans also absorb a large part of the Earth's heat, causing "thermal expansion" of the water. As water temperature rises, the space between water molecules increases, leading to an increase in volume. On a global scale, the increasing volume of ocean water is leading to the sea level rising.

Timelapse depicting effects of projected sea level rise
Time lapse of how projected sea level rise will affect the North Carolina coast. (Created by NC Office of State Archaeology with images from the National Oceanic and Atmospheric Administration, 2022)

Changing habitats is one of the greatest threats of rising sea levels. Marine plants and animals adapt to habitats at specific depth ranges. As these ranges shift native species will begin to move to more habitable areas. Shoreline and coastal habitats are also threatened, as rising sea levels submerge them. These submerged environments also become more turbulent with increased water and wave energy. Land and tidal species must move inland to find safer homes that are not underwater. Saltwater also enters existing freshwater systems, disrupting wildlife that relies on freshwater.

Damaging floods result from rising sea levels. As ocean waters push into existing bodies of water, the surrounding areas are more prone to regular tidal flooding. Tropical and extratropical storms bring lots of energy and storm surges to the coast. Flooding resulting from these storms can affect the coast and inland.

The North Carolina coast is experiencing sea level rise unequally. The northern coastline is seeing a rate of sea level rise twice that of the southern coastline. Models show that the lowlands of northeastern NC will disappear with only eight more feet of sea level rise. This includes most of Camden, Carteret, Currituck, Dare, Hyde, Pamlico, and Pasquotank counties.

Impacts on Archaeological Sites

Sea level rise impacts archaeological sites both on land and underwater. As the depth of water above submerged sites increases, the environment in which these sites lie changes. Shallow-water sites become underwater sites. Underwater sites become further out to sea. Shifting ocean currents and changing environments can have detrimental effects on these sites.

Erosion of the marshline on Town Creek in Brunswick County
Erosion of the marsh line on Town Creek in Brunswick County. Visible within the mud are remains of a built wooden structure, likely related to plantations that lined Town Creek. The rise in sea level has caused more water to move along the shoreline, breaking off large sections of marsh and exposing buried structures. (Image by NC Office of State Archaeology, 2022)

Saltwater intrusion into freshwater systems introduces chemical-level changes to site stability. Salt causes extensive corrosion of iron underwater. Salt also enters land sites through saltwater in the groundwater. The introduction of salt to already corroding artifacts speeds up the process.

Temperature is only one characteristic of the ocean that is experiencing change. Other shifting properties include oxygen levels, saltiness, and acidity. These things have a great impact on marine life, archaeological sites, and ocean currents.

Atmospheric carbon dioxide and air temperature play a large role in ocean chemistry. Carbon dioxide holds atmospheric heat and dissolves in water. Oceans absorb most of the global heat, warming the waters to a much greater depth. Warmer water holds less oxygen, leaving fewer habitable areas for marine life that need it. Through chemical processes, dissolving carbon dioxide also produces hydrogen which increases water acidity.

Warming air affects salt concentrations in different parts of the world.  Polar and tropical seas generally have a lower salt content due to freshwater mixing from ice formations, rivers, and rain. As evaporation pulls water from oceans, it leaves behind saltier water in these regions.

North Carolina sits generally in the middle between the tropics and the pole. Because of this location, offshore ocean temperatures have been and will continue to rise. Salt concentrations will increase as evaporation from warm air temperatures increases. Local acidity will increase, and oxygen will decrease as the waters warm.

Impacts on Archaeological Sites

Changes in ocean properties affect archaeological sites both underwater and in coastal areas. Native species leaving the area due to inhospitable environments encourage new species. Non-native species may use the environment in different ways and damage submerged sites. Marine organisms are particularly attracted to metal structures, gathering and creating artificial reefs. The weight of these colonies can become too much and collapse a submerged site or wreck.

Some marine life, such as microbes, use chemicals in iron and steel for energy. In doing so, they corrode structures and lead to site degradation. Other marine life uses organic matter like wood ship timbers for energy. These organisms may attach to the outside or burrow into wood, leading to decay.

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The engine portion of the wreck of Condor covered in concretion and sea life. Concretion develops from chemical interactions between ocean salinity, sand, and iron corrosion. (Image by NC Office of State Archaeology, 2017)

The chemical properties of the ocean itself lead to site degradation.   Lots of chemical reactions occur between the elements in metal and seawater. Higher salinity, acidity, and lower oxygen increase corrosion of metal site components. Thinning metal components lead to the collapse of site structures. Concretion, a byproduct of iron corrosion, adds weight to artifacts on a site. This weight, like that from colonizing life, can become too heavy and collapse submerged sites. The effects of these chemical properties on the degradation of wooden sites are currently understudied.

Extreme weather events are more severe than everyday weather. These events include hurricanes, droughts, seasonal storms, heatwaves, and wildfires. Changes in precipitation and air and water temperature influence these extreme events. Extreme weather events vary by location. Some places experience hurricanes, but not snowfall. Others experience snowfall but not hurricanes.

With climate change, extreme weather events will become more frequent and detrimental. Droughts, wildfires, and heatwaves worsen as temperatures rise and evaporation increases. Hurricanes and storms become stronger as tropical waters warm. Both lead to heavy precipitation and extensive inland flooding. While winter storm will become more intense, they will decrease in frequency. This is because warming temperatures will lead to warmer days and nights year-round. Areas of high elevation will see stronger snowstorms as more water is in the atmosphere.

Flooding in the River Arts District of Asheville, North Carolina
Flooding in the River Arts District of Asheville, North Carolina. This extensive flooding in Asheville and throughout the river valleys of western North Carolina happened because of the Hurricanes Frances and Ivan. In 2004, Hurricanes Frances and Ivan both made landfall in the Florida Panhandle before moving over western North Carolina, bringing significant winds and rains. (Image by NC Historic Preservation Office, 2004)

We will feel the effects of extreme weather change across North Carolina. Tropical storms will bring heavier rain, stronger winds, and more flooding. Seasonal storms will bring heavier rains and more coastal flooding. Snow and ice storms will decrease across most of the state but be more severe when they occur. The state is already experiencing an increase in droughts and heatwaves. This dryness will contribute to an increase in wildfires.

Impacts on Archaeological Sites

Hurricanes bring strong winds, heavy rain, and extensive storm surge to our coast. This energy disturbs archaeological sites in its path. Shoreline sites erode into the ocean from water and wave energy. As heavy winds bring down trees, their roots disturb artifacts and structures. Storm surges and heavy rains increase inland flooding, moving soil and artifacts out of context. Moisture from floods also encourages mold growth on exposed structures.

A tree uprooted during a hurricane damaged a cemetery plot at the Old Burial Ground in Beaufort, NC
Uprooted tree showing the historical remains of a brick structure underneath in the Old Burial Grounds in Beaufort, North Carolina. Several large trees, including this one, were uprooted in the cemetery during Hurricanes Florence and Michael in 2018. This uprooting uncovered and disturbed historic burials and structures. (Image by NC Office of State Archaeology, 2018)

Hurricanes also destroy underwater sites. The high wave energy interacts with the sea floor, moving sediment. Extensive sediment movement can cause sites to collapse or move. This movement can bury or uncover sites, changing the site environment. Wave energy can move artifacts and fracture exposed structures.

Droughts and heatwaves result in a drying of environments. Diminishing lakes and rivers can expose submerged sites once protected by water. This drying also pulls moisture from artifacts and structures, leading to breakage and collapse. Dry landscapes are much more susceptible to wildfires. Fires can burn through exposed and buried structures, decimating them. The heat from fires can even alter stronger artifacts, like melting metal and glass.

Freezing conditions from winter storms, snow, and ice can lead to surprising degradation. Porous artifacts and structures soak up moisture near them. Infrequent extreme winter events put cultural materials through a cycle of freezing and thawing. Water expands when it freezes, and artifacts can disintegrate as the ice melts. Snow and ice also exert unusual weight on site structures, compressing and leading to collapse.

Main image: Flooding and erosion of the marsh line on Town Creek in Brunswick County. (Image by NC Office of State Archaeology, 2022)

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This material was produced with assistance from the Emergency Supplemental Historic Preservation Fund, administered by the National Park Service, Department of the Interior. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Department of the Interior.