Climate has left its mark in several places on the planet—in the chemical and physical structures of the land, the oceans, and life. These climate artifacts, called climate proxies, reveal climate patterns that can extend backward in time hundreds of thousands, even millions, of years. When this proxy evidence is combined with present-day observations of the Earth's climate and is entered into computer models, this paleoclimatic data (paleo means "ancient") can help scientists predict future climate change. This chapter illustrates how clima-tologists can reconstruct a clearer picture of past climates by unraveling the stories of the various landforms on the Earth's surface. The Earth's geologic record represents a rich treasure trove of information reflecting the ways in which climate has left its lasting mark on the Earth's geographic features.
Evidence is reflected in various landforms and landscapes detailing the Earth's past temperature, moisture, humidity, and atmospheric cir culation patterns. These climate proxies are in the form of specific geomorphic landforms. Geomorphology is the study of landforms and the various processes that create and shape them. These resultant landforms are the result of climatic variables such as the mean annual, maximum and minimum, and seasonal distribution of temperature, net evaporation, and levels of precipitation on land and currents, salinity, nutrient level, and temperature in the oceans.
When scientists reconstruct past climate, they do it in a methodical way. The first phase consists of collecting the actual proxy data. Once collected, they are analyzed, measured, and then calibrated (adjusted to fit) with present-day climate records. When climatologists calibrate data, they assume that the laws of ancient climate behaved in a similar way to modern climate. They are aware, however, that past climates could have behaved somewhat differently and that some error could be introduced during the reconstruction, but they do their best to ensure the data are interpreted as accurately as possible. The data from the ancient climate are then compared to present climate so they can be interpreted.
According to the U.S. Geological Survey's (USGS) Geologic Division, climates are always changing, and understanding these changes and their effects are some of the most challenging issues society has to deal with today. This is especially the case with global warming. They point out that it is a major issue facing society today and deserves a high degree of attention in the form of research because many unanswered questions remain. One of the biggest uncertainties is the primary driving source—how human activity affects the Earth's natural cycles. Other uncertainties include the triggers of rapid climate change and how people can plan for, adjust to, and protect themselves from the climate if it does change with little warning.
Again, it comes to understanding the climate's past in order to make sense of it and predict its future. Looking at the Earth's geologic and geomorphic past is one way to do this. The forces on the surface of the Earth that shaped its features can give climate scientists significant clues about what the climate was like on Earth in ancient times.
Geologists know that climate has a major influence on the shape of the landscape. Different factors work on the landscape over time, shaping it in unique ways, such as water, wind, energy, gravity, and temperature. A desert landscape, for example, is very distinct. If relics of arid land features, such as dunes, alluvial fans, pediments, desert pavements, and scoured and eroded sedimentary surfaces, appear in a humid climate, this is conclusive evidence that the area was arid at some time in the past. Likewise, glacial features are distinct, and their presence writes another specific story about what past climate was once like.
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