Environmental Variability and Climate Change
Environmental Variability and Climate Change
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