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How do we measure past climate?

Environmental recorders have been developed to estimate past climate conditions and thus extend our understanding far beyond the 150-year instrumental record of climate change. Annual records of climate have been preserved in tree rings, locked in the skeletons of tropical coral reefs, extracted as ice cores records that have been frozen into glaciers and ice caps, and buried in laminated sediments from lakes and the ocean. Referred to as "proxies," these sources of climate information are calibrated and tested using the 150-year instrumental record of climate change.


What is paleoclimatology?

Paleoclimatology is the study of past climate prior to the existence of instrumental records. NOAA is particularly interested in the climate of the last few thousand years because it helps establish the range of natural climatic variability in a period prior to global-scale human influences on climate. Paleo "proxies" such as tree rings, coral reefs, ice cores, and sediments allow us to reconstruct past climate patterns without thermometers or rain gauges.


What do different paleo proxies tell us about climate variability?

Animation showing paleoclimatic researchTree Rings
Trees record information about past environments and climate in their annual growth rings. Dendrochronologists study tree rings to gather records of past temperature and drought.


Corals
Corals build calcium carbonate skeletons over many years and are sensitive to water temperatures and other environmental factors. Their skeletons record annual information on past climate and ocean circulation.

Ice Cores
Scientists travel to the far reaches of the earth to collect data embedded in ice cores. Important ice caps that reveal past climate patterns are found in Greenland, Tibet, the Andes and Antarctica.

Paleoclimatic data sources also include packrat middens, pollen, ocean and lake sediments, speleothems, geomorphic features and historical sources including diaries and journals.



Temporal Scope and Potential Information from Paleoclimatic Proxies
The following chart shows how different natural archives record varying time intervals, cover different time periods and provide insight into a variety of indicators of climatic conditions.


Temporal Scope & Potential Information from Paleoclimatic Proxies
Proxy Type
Sampling Interval
(min.)
Temporal
Scope
(order: yr)
Temp.
Precip.
or water
balance
Chemical
composition
(air or water)
Biomass
or vegetation
Volcanic
eruptions
Sea Level
Solar
Activity

Historical Records

day/hr
~103
X
X
X
X
X
X
X
Tree Rings
yr/season
~104
X
X
0
X
X
0
X

Lake Sediments

yr to 20 yr
~104~106
X
X
0
X
X
0
0
Corals
yr
~104
X
X
X
0
0
X
0
Ice Cores
yr
~5 X 105
X
X
X
X
X
0
X
Pollen
20 yr
~105
X
X
0
X
0 0 0
Speleothems
100yr
~5 X 105
X
X
X
0 0 0 0
Loess
100yr
~106
0
X
0
X
0 0 0
Geomorphic features
100 yr
~106
X
X
0
0
X
X
0
Marine sediments
500 yr
~107
X
X
X
X
X
X
0

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Last Updated Wednesday, 20-Aug-2008 11:22:39 EDT by paleo@noaa.gov
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