Caption: Coral reefs are sensitive to a variety of environmental changes. Smithsonian astronomers Willie Soon and Sallie Baliunas reviewed more than 200 studies of coral, glacier ice cores, tree rings and other indicators to trace changes in the world's climate over the past millennium. They found that the 20th century is NOT the warmest of the past 1000 years. (Credit: David A. Aguilar, Harvard-Smithsonian Center for Astrophysics) JPEG (23K) High Resolution JPEG (272K)
	Caption: Studies of tree rings can yield yearly records of temperature and precipitation trends. Researchers drill small cores to obtain samples. (Credit: Tony C. Caprio) JPEG (38K)
	Caption: Glacier ice cores record temperature and precipitation trends over longer time scales of several decades to a century. (Credit: Kendrick Taylor, Desert Research Institute) JPEG (181K)

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