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Environmental Variability and Climate Change

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Tools of the Trade<br />

“Except for the observations made over the last 130 or so<br />

years at weather stations <strong>and</strong> on ships, our knowledge of<br />

past climates is based on records kept in sediment <strong>and</strong><br />

ice. The task of the paleoclimatologist is to decipher these<br />

proxies.”<br />

W. Broecker, 1993<br />

Paleo-environmental archives <strong>and</strong> proxies<br />

Paleo-environmental archives such as ice caps,<br />

marine <strong>and</strong> lake sediments, trees <strong>and</strong> long-lived corals<br />

preserve records of past environmental changes.<br />

These <strong>and</strong> other archives, including documentary<br />

records, provide information about changes in the<br />

atmosphere, ocean, cryosphere, biosphere, <strong>and</strong> the<br />

dynamics of interactions among them. Deciphering<br />

the evidence that natural archives contain often<br />

involves extensive field-based research. Some of<br />

Bachalpsee, in the<br />

Swiss Alps, is one of<br />

many lakes with an<br />

annually laminated<br />

sedimentary record of<br />

past environmental<br />

change.<br />

photo: André Lotter<br />

the key natural archives of past global change are<br />

rapidly disappearing, lending urgency to the task<br />

of retrieving them.<br />

Paleo-environmental reconstruction requires that<br />

the properties measured in natural archives (proxies)<br />

be quantitatively translated into environmental parameters.<br />

For this approach to work the proxies must<br />

be rigorously calibrated against direct observations,<br />

such as July air temperature, sea-surface salinity or the<br />

makeup of vegetation cover. Thus, a period of over-<br />

4 IGBP SCIENCE No. 3 PAGES – Tools of the Trade

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