Environmental History Resources

Research methods in environmental history – The case of climate and landscape history

Traditional history as it developed during the 19th century depended on written documents that were produced sometime in the past. Originally these sources included only “official documents” produced by government and kings as well as merchants and traders, such as charters but also correspondence. During the 20th century the nature of historical studies changed radically and who is now surprised when historians use economic ideas and data in their studies, or use insights from anthropology, sociology and gender studies?

Conventional history based on written sources has its limits when we study the interaction between humans and society in the past. There are several problems, though not unique to environmental history, that go beyond historical sources used by most historians. The time span of many processes that affect the relations between human culture and the environment are often extremely long, hundreds or even thousands of years, and exceed written records. Another obstacle is that lliteracy was, and often still is limited in many parts of the world and during most periods in the past, for example Prehistory in Europe. But even in literate societies environmental changes/impacts are often not recorded because these are seen as normal processes and activities that form the backdrop of day-to-day life. Only some extreme disastrous events such as volcanic eruptions, earthquakes or flooding are sometimes recorded. In general we may conclude that the natural environment in which human history unfolds is poorly served by written history – we need collaboration between humanities and natural sciences to tell their stories! What is needed, apart from documentary historical evidence, are the tools of the environmental and natural sciences to unravel untold stories. What kind of evidence and tools are available to the environmental historian? Let’s examine some of the tools available to the climate and vegetation historian.

Written sources
For climate and vegetation history we can of course rely on written sources, paintings, photographs and recorded instrumental observations. Historical documents contain a wealth of information about past climates but also descriptions of the landscape used to reconstruct climates and landscape change dating back several hundred years back in time. Observations of weather and climatic conditions as well as the landscape and resources such as forests and peat deposits (for fuel) can be found in farmers, travellers and gamekeepers diaries, newspaper accounts, ships logs and other written records. Landscape paintings can provide information about woodland cover, use of the land and perceptions of landscapes. When properly evaluated, historical data can yield both qualitative and quantitative information about past climate and landscape change.

Greenland Ice Core showing annual layer structure.
Credit: Anthony Gow, US Army Corps of Engineers,
Cold Regions Research and Engineering Laboratory.

Ice cores
Located high in mountains in glaciers and deep in polar ice caps, such as on Antarctica or Greenland, ice has accumulated from snowfall over many centuries. Glacial ice contains dust, air bubbles, or isotopes of oxygen that can be used to interpret the past climate at the time that the snow fell that formed the ice. The thick layers of ice that accumulated over thousands of years provide a wonderful record of the past global climate and scientists drill deep into icecaps to collect ice cores to get access to this data. Two well known examples of such ice core projects are the Greenland Ice Core Project and the Vostok Ice Core Project in Antarctica. Both cores provide climate data for tens of thousands of years.

Conifer pollen

Pollen
Palynology is the analysis of fossil pollen used for the reconstruction of past vegetation and climates. Each species of plants produces pollen grains, which have a distinct shape. These shapes can be used to identify the type of plant from which they came. Since pollen grains hardly rot, they are well preserved in the sediment layers that form at the bottom of a pond, lake or in blanket peat. An analysis of the pollen grains in each layer can tell us what kinds of plants were growing at the time that the sediment was deposited. Inferences can then be made about the climate based on the types of plants found in each layer. Pollen can also be used to determine human impact on environments such as deforestation or the extent of agriculture by counting the number of tree or cereal pollen.

Lake and ocean sediments
Billions of tons of sediment accumulate on the ocean floor and in lake basins each year. Ocean and lake sediments consist of biological and other materials that were produced in the lake/ocean or that washed in from nearby land. These materials are deprived of oxygen and are thus preserved as tiny fossils and chemicals in the sediments and can be used to interpret past climate. Scientist drill cores of sediments from the sediments buried below the ocean floor in order to get a sequence of changing climate over time.
The most important fossils are shells from so called forams (foraminiferan), tiny creatures living in the worlds oceans that produce shells which sink to the ocean floor after the creatures die. There are different types of forams living in water of different temperature. Particular forams found in different layers are a measure of the temperature at a certain time. The carbon and isotope content of the form shells provides information about the composition of the atmosphere in the past.

Coral reefs
Corals build their hard skeletons from calcium carbonate, a mineral extracted from seawater. The carbonate contains oxygen and the isotopes of oxygen, as well as trace metals, that can be used to determine the temperature of the water in which the coral was formed as well as the composition of the atmosphere at a certain time. These indirect temperature recordings can then be used to reconstruct climate during the period of time that the coral lived.

Raised or drowned beaches
Raised beaches or drowned beaches are former beaches located above or below present day sea levels and are formed when sea levels drop or rise, or when land levels rise or fall. This could be due to an actual fall in the water level such as may be caused by the formation and melting of extensive ice sheets during and after a major glaciation (ice age). The disappearance of ice sheets also results in a so-called glacial rebound; the springing back of land after the weight of the ice has disappeared. This happens for example in Scotland and Scandinavia. The dating of raised beaches can tell us something about the climate on earth and related sea level changes. Fossil coral reefs stranded on top of islands can also be used for the same purpose.

Tree rings

Tree ring
Dendrochronology or tree-ring dating is the method of scientific dating based on the analysis of tree ring growth patterns. Since tree growth is influenced by climatic conditions, such as temperature and precipitation, patterns in tree-ring widths, density, and isotopic composition reflect annual variations in climate. In temperate regions where there is a distinct growing season, trees generally produce one ring a year, and thus record the climatic conditions of each year. Trees can grow to be hundreds to several thousands of years old and can contain annual records of climate for the centuries to millennia that they lived.

Other kinds of documents
In essence environmental history uses complementary sources, called proxy or indirect data, to written documents that conventional historians rely on. These can all be used in different ways to put together a complete picture of the historical puzzle.
Proxy-data documents changes in the environment and interactions between nature and culture over time. On the other hand written documents and artefacts of human culture documents us. Taken together proxy-data, artefacts and documents combined tell us more about the past interaction between environment and culture than either could do alone. For this reason, historians who want to understand our relationship with nature in the past must collaborate specialists from other disciplines including archaeologists, anthropologists and the natural sciences.

Further reading

Arnold, John, History: A Very Short Introduction (Oxford: Oxford University Press, 2000).

Cronin Thomas M., Principles of Paleoclimatology: Perspectives in Paleobiology and Earth History (New York: Columbia University Press, 1999)

David Herlihy, “Climate and Documentary Sources: A Comment”, The Journal of Interdisciplinary History, Vol. 10 (1980) no. 4, pp. 713-718.

Lamb, H.H., “How can we reconstruct the past record of climate?”, in: Climate History and the Modern World (London: Methuen, 1982), Ch. 5, pp. 67-100.

Roberts, Neil, “Reconstructin Holocene Environments”, in: The Holocene: An Environmental History (Oxford: Blackwell, 1998), Ch 2.

Westbroek, Peter, Life as a Geological Force: Dynamics of the Earth (New York: Norton, 1991).