figure 2: summary of the resolution and time span of record for proxy data sources. the top horizontal axis indicates the period for which the proxy data can be collected (e.g., tree rings can provide information on the climate for periods of hundreds to thousands of years). the bottom horizontal axis indicates the resolution available for the proxy data (e.g., tree rings provide annual resolution of the climate).
Coral- The climate each year over the past few hundred years for a small island located in the Pacific Ocean near the equator
Tree rings- The climate for each year over the past 200 years in the heavily vegetated northwest United States
Ice cores- The climate of Antarctica for the past 100,000 years
Ocean sediments- The climate of the North Atlantic Ocean for the past million years
Lake sediments- The climate of the last 10,000 years in the southeastern United States - with several inland water bodies such as lakes
While scientists must consider the most appropriate proxy data source to use, they are also limited by the proxy data sources available. For example, even though ice cores are a powerful proxy data source because they contain air bubbles and material such as dust, they are limited to cold regions and the past several hundred thousand years. Moreover, the farther back in time one seeks to reconstruct a climate, the fewer proxy data sources that are available. The ability to reconstruct a comprehensive global record of climate therefore becomes more difficult the farther back in time one seeks to reconstruct the climate.