Author: Allyson Ropp, Historic Preservation Archaeology Specialist
Temperature, the measure of how hot or cold the air is, has always changed on our planet. Even before humans walked the Earth, our planet went through cycles of warming and cooling. During these times, glaciers and ice sheets expanded and contracted, causing the sea level to rise and fall. Nowadays, we are noticing an accelerated global increase in average temperature, and it's expected to increase by another 1.5 degrees Fahrenheit by the year 2100. Though it may not sound like much, even a small increase in atmospheric heat can have a significant impact on the world.
This is global climate change, and temperature is a large part of it. The increase in temperatures happens because of something called the greenhouse gas effect. Our planet's atmosphere acts like a protective cover, allowing some of the sun's energy to come in while reflecting the rest away. However, certain gases in the atmosphere can trap some of this energy, creating a concentration of warmer air. This trapped heat spreads around the Earth, leading to overall warming of the planet.
As temperatures rise, several feedback loops come into play, contributing to even more warming. For example, warmer temperatures cause ice and snow to melt, and the darker oceans then absorb more heat from the Sun. This, in turn, leads to higher ocean temperatures and rising sea levels. Warmer temperatures also affect large-scale climate patterns, like precipitation and evaporation. As the temperature increases, more water evaporates, leading to drier soil. The increased evaporation also means more water is held in the atmosphere, resulting in more intense rainfall. This cycle of drying and heavy rainfall can lead to changes in weather patterns.
The impact of warming on archaeological and cultural heritage sites is concerning. For sites located underwater or along the coast, warmer temperatures cause rising sea levels and changes in their surrounding environment. This alters the exposure of these sites to different conditions and processes, which can be damaging. (Visit March's blog to learn more!)
Terrestrial sites are also negatively impacted. Warmer temperatures can lead to increased evaporation, drying out the soil and subjecting previously buried archaeological remains erosion and deterioration. Water evaporating from sediment can even cause the land to sink, a process called subsidence, which can collapse site features and expose them to further damage. At the artifact level, evaporation can draw water out of exposed remains, such as wood, leading to cracks and damage. Freezing-thawing cycles during winter can also widen these cracks, weakening artifact and structures.
Warmer temperatures also affect various organisms that live around these sites. Animals, plants, and microorganisms have specific temperature preferences, and as temperatures change, their habitats will shift. This can introduce new species to the site, and some of them might cause physical damage to artifacts and structures. Plants and animals may move artifacts and structures through burrowing habitation, and root development. Microscopic organisms can also deteriorate materials over time by consuming them for energy.
Main image: 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)
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.
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