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Proxy Data

Proxy data is data that paleoclimatologists gather from natural recorders of climate variability, e.g., tree rings, ice cores, fossil pollen, ocean sediments, coral and historical data. By analyzing records taken from these and other proxy sources, scientists can extend our understanding of climate far beyond the 140 year instrumental record.

Listed below are some widely used proxy climate data types:
grapes image from Bradley 1991 photo

Historical Data:

Historical documents contain a wealth of information about past climates. Observations of weather and climatic conditions can be found in farmers' logs, travellers' diaries, newspaper accounts, and other written records. When properly evaluated, historical data can yield both qualitative and quantitative information about past climate.

The example above demonstrates how historical grape harvest dates were used to reconstruct summer temperatures (April - September) in Paris from 1370 - 1879. [From Bradley, 1990; based on data Le Roy Ladurie and Baulant, 1980.]
coralb image courtesy of NOAA Paleo Slide Sets


Corals build their hard skeletons from calcium carbonate, a mineral extracted from sea water. 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 grew. These temperature recordings can then be used to reconstruct climate during that period of time that the coral lived.

To learn more about the study of corals please visit
pollen image courtesy of NOAA Paleo Slide Sets

Fossil Pollen:

Each species and genus 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 are well preserved in the sediment layers that form in the bottom of a pond, lake or ocean, an analysis of the pollen grains in each layer tell us what kinds of plants were growing at the time the sediment was deposited. Inferences can then be made about the climate based on the types of plants found in each layer.

To learn more about fossil pollen, please visit the following:
treering image courtesy of NOAA Paleo Slide Sets

Tree Rings:

Since tree growth is influenced by climatic conditions, patterns in tree-ring widths, density, and isotopic composition reflect 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 thousands of years old and can contain annually-resolved records of climate for centuries to millennia.

To learn more about tree rings please visit the following:
ice image courtesy of NOAA Paleo Slide Sets

Ice Cores:

Located high in mountains and deep in polar ice caps, ice has accumulated from snowfall over many centuries. Scientists drill through the deep ice to collect ice cores. These cores contain dust, air bubbles, or isotopes of oxygen, that can be used to interpret the past climate of that area.

To learn more about ice cores please visit the following sites: The Australian Antarctic Division
sedimentimages courtesy of NOAA Paleo Slide Sets

Ocean & Lake Sediments:

Between 6 and 11 billion metric tons of sediment accumulate in the ocean and lake basins each year. Scientists drill cores of sediment from the basin floors. Ocean and lake sediments consist of materials that were produced in the lake/ocean or that washed in from nearby land. These materials (preserved tiny fossils and chemicals in the sediments) can be used to interpret past climate.

To learn more about ocean and lake sediments, please visit the following:
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