If scientists want to understand climates going back further than 200 to 300 years, they must proxy information. This information comes from Earth’s natural archives, such as tree rings, coral reefs, pollen data, cave formations, and lakes and sea shores. But it also comes from human sources such as historical documents.
By decoding these clues from the distant past, scientists attempt to reconstruct past climate conditions. Analyzing patterns of change from past climates helps scientists understand the ways in which today's climates are changing.
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