Research Strategies for the U.S. Global Change Research Program (1990) / Chapter Skim
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3 Earth System History and Modeling
3 Earth System History and Modeling
Pages 67-107
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From page 67... ...
Observations often challenge our constructs of how the earth operates as a system and provide a valuable time perspective for understanding the consequences of future environmental change. Specific important geoscience contributions to global change research include the follow~ng: 1.
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From page 68... ...
Parametersa Historical records Daily 103 T P B V M L S Tree rings Seasonal 104 T P Ca B V M L 5 Ice cores Polar lyr 1Os TPCaBVMS Mid-laUtUde 1 yr 104 T P Ca B V M S Corals 1 yr 105 T CwL Pollen and other 100 yr 1Os T P B fossils Sedimentary deposits Aeolian 100 yr 106 T P B V M Fluvial 1 yr 106 P VML Lacustnne 1 yr 106 TB M Marine 100 yr 107 TCw B M Soils 100 yr 1Os TPB V aParameters ate as follows: T= temperature P = precipitation, effective moisture, or humidity C = chemical composition of air (a) or water (w)
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From page 69... ...
Additional studies have shown that natural variations in carbon dioxide and abrupt transitions are an integral part of glacial-interglacial climatic changes (Barnola et al., 1987; Broecker and Denton, 1989; Fairbanks, 1989~. Although significant strides have been made in understanding past environments, there are a number of important problems that require enhanced study.
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From page 70... ...
Implementation of the Research Plan Previous research experience demonstrates that progress in understanding past environments has resulted from both individual research projects and more organized efforts such as CLIMAP and COHMAP. Although individual research projects will continue to be an important component of future investigations, it is also apparent that fully successful implementation of some elements of the research plan will require some sustained
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From page 71... ...
development of a high-resolution global network of climate fluctuations for the last 1,000 to 2,000 years, with special emphasis on the Little Ice Age (LIA) and on process studies for some key regions and (2)
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From page 72... ...
1400 1600 1800 2000 _ , , _ Phenological Temperature West China Tree Rings ;~ an If, Winter Temperature, , ~ -4t Yangize Valley ~l ~Counties affected .. 400 - by drought c_, 600 -V'v' ~ o x ~2 3 4 -28 o -29 so -30 1.5 CD 0.0 so -1.5 lot on o o.o a' ~ - 0.5 - 1.0 Dust Rain Frequency ~: Quelccaya Ice Cap, Peru _ South Pole Station, Antarctica 4~ ~_ 1000 1200 1400 1600 1800 2000 Years A.D.
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From page 73... ...
At present the Holocene data base is too sparse to map specific responses at the level of detail necessary to elucidate cause-and-effect relationships. Three likely mechanisms for climatic change on decadal time scales include solar
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From page 74... ...
Little Ice Age A period of special interest is the Little Ice Age (approximately 1450 to 1880 A.D.~. In many areas, maximum cooling occurred in the seventeenth century, although not all regions appear to have cooled synchronously.
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From page 75... ...
The abundant highresolution data for the LIA are particularly appropriate for investigating potential forcings and the climatic and biospheric responses. Regional Process Studies Knowledge of the processes responsible for local changes inferred from proxy records is essential for accurate interpretation.
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From page 76... ...
This research will require additional information on tropical rainfall from tree rings, ice cores, and upwelling variations as recorded in coral reefs.
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From page 77... ...
At present the models can theoretically generate variance on decadal and longer time scales, but key parameterizations in the models are not well constrained by observations. Approaching the problem from both an observational and a modeling viewpoint for the last 500 years may provide additional insight to processes occurring on shorter time scales.
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From page 78... ...
I _ 1 _, _ I ~ I _ ~ I _, _ ~ _ ~ _ I _ Torewell Stode _ I _ ~ ~ _ I _, _ I _ ~ _ ~ _ ~ _ ~ _, _ ~ _ _ ~ _ ~ _ ~ _ ~ _ ~ _, _, _ ~ _, _, ~ _ ~ _ ~ _ ~ _ I - ~ - 1 - I - I - I - ~ - I - I - I -1-1 - ~ -1-1 -1 l ~ I Connereville Interalade | ~, _, , _, , ._, , _, _, _,, _ `~1 - ' - ~ - , - 1 _ ~ _, _, _, _ ~-`~- Foyctle SIode -- l ~ _ ~ _ , _ , _ , _ ~ _ , _ _ O 1000 2000 3000 4000 5000 6000 7000 8000 9000 Q a, 10,000 11 000c o 12 000O ._ o 13 000~ 14 000 15 000 I6 000 '7 000 t8 000 19,000 20 000 21 000 22 000 FIGURE 3.2 Evidence for repetition of millennial-scale climate oscillations at intervals of 2,000 to 3,000 years over the last 20,000 years. Analysis of any specific event, such as the Little Ice Age or Younger Dryas, must take into account the characteristic time scale of these oscillations.
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From page 79... ...
These subtasks fall naturally into different time scales, with processes operating on one time scale sometimes affecting
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From page 80... ...
The observational needs and modeling requirements are discussed for each. Abrupt Changes Some of the most spectacular examples of abrupt climatic change in the earth's history are known to have occurred at the end of the last glacial stage (14,000 to 10,000 B.P.~.
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From page 81... ...
transition to warm conditions may have occurred in as little as 20 years (Dansgaard et al., 1989~. Abrupt transitions found in the Dye 3 Greenland ice core between 40,000 and 30,000 B.P.
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To clarify these issues, it is highly desirable to gather ice core records from regions of higher accumulation where air closure times are shorter and time scales can be established with greater confidence. Any evidence linking
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Understanding of the spatial extent and synchroneity of biotic responses to both abrupt and gradual climatic changes must be greatly improved. · to determine the temporal history of millennial-scale fluctuations that may be linked to abrupt transitions.
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From page 84... ...
(COHMAP Members, 1988; Mitchell et al., 1988~; (3) clarifying factors responsible for high-latitude climatic change in the southern hemisphere at 18,000 B.P.
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The Last Glacial Cycle (Last 130,000 Years) Many of the processes that can be studied over the carbon-14 time scale provoke explanations that should be applicable to other time intervals of climatic change during the Quaternary.
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From page 86... ...
temperature record at the end of the last interglacial. (Reprinted, by permission, from T.J.
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From page 87... ...
Convincing evidence now exists for changes in atmospheric carbon dioxide during the past 150,000 years (Barnola et al., 1987; Neftel et al., 1988~. Ongoing work is documenting variations in methane, nitrous oxide, and the oxygen isotope composition of ancient atmospheres; the data show that large changes in atmospheric carbon dioxide have occurred that are approximately in step with the major climatic changes of the last 150,000 years and that significant changes have occurred in other natural greenhouse gases.
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From page 88... ...
· to conduct detailed comparisons of ice core, marine, and continental records. Some problems of particular interest that might be examined include the interactions of terrestrial ecosystems, environmental change, and atmospheric composition, and the climatic effect of possible variations in cloud cover.
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From page 89... ...
It is also important to determine which ice sheets contributed to the sea level rise both Greenland and the West Antarctic ice sheets have been suggested (Koerner, 1989; Mercer, 1978~. These two topics-warmth and sea level are critically related because knowledge of the magnitude of warming may help calibrate the sensitivity of the cryosphere to warming trends and thus enhance our ability to predict the course of future changes in sea level.
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From page 90... ...
At present knowledge of the land record beyond the range of carbon-14 dating is rather limited. In Europe, studies of several exceptionally long stratigraphic records have revealed the responses of vegetation to climatic changes throughout the entire last glacial-interglacial cycle (e.g., Guiot et al., 1989~.
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From page 91... ...
For example, studies clearly indicate that there are significant phase offsets among the different components of the climate system (e.g., Imbrie et al., 1989~. Although significant progress has already been made on this topic, better information about some variables is needed to constrain models of the Pleistocene ice ages.
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From page 92... ...
Topics of special importance involve the response of the earth system during times when climates were substantially warmer than modern and intervals during which the climate system experienced rapid and large changes. An especially important contribution involves the biospheric response to these large changes, as the geologic record provides the only information available on the relation between extinction events and environmental change.
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From page 93... ...
. o 20 40 60 80 100 MILLIONS OF YEAtlS 20 15 0 [LI 10 5 0 AL o In FIGURE 3.6 Deep-water oxygen isotope record for the last 100 million years, illustrating die long-term cooling trend arid the tendency for the system to evolve Trough abrupt transitions (arrows)
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From page 94... ...
Whenever possible, sampling intervals of time series should be fine enough to detect forcing functions on orbital time scales. At a minimum, synoptic studies should provide regional resolution comparable to model output.
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From page 95... ...
The geologic record represents the only realistic test for the parameterizations in these models. Climate-Biosphere Connections During Abrupt Changes A number of significant and relatively abrupt transitions have occurred during the last 100 million years (Figure 3.6~.
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From page 96... ...
The development of extensive northern hemisphere ice sheets at about 2.5 Ma is a rapid transition from relatively ice free conditions in polar regions of the northern hemisphere. The 2.5-Ma event follows closing of the Isthmus of Panama, opening of the Bering Strait, and continued mountain building in Tibet and western North America (Ruddiman and Raymo, 19883.
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From page 97... ...
Observations are needed to develop a comprehensive reconstruction of the physical changes in the environment across the abrupt events. Detailed time series are needed for key variables and in key regions in order to delineate the timing of the system response and the relationships between different components.
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From page 98... ...
These may range from high (>18,000 feet) , remote ice caps in the tropics and mid-latitudes to the polar ice caps, which are up to 3,000 m thick.
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From page 99... ...
The need for more marine cores will require additional drilling equipment and more efficient use of existing facilities. Currently, sediment sequences from the sea floor are recovered principally by the Ocean Drilling Program (ODP)
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From page 100... ...
New geochemical methods may prove invaluable. For example, a new technique for estimating sea surface temperature or bottom-water temperature would be invaluable for separating the ice volume, salinity, and temperature signals from the oxygen isotope record in marine carbonates.
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From page 101... ...
for projects requiring considerable coordination (e.g., the global network for the last 1,000 years (see the section "Global Network of Environmental Change") , the Little Ice Age (see the section "Little Ice Age")
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Labeyrie (eds.) , Abrupt Climatic Change.
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From page 103... ...
1988. Climatic changes of the last 18,000 years: Observationsandmodelsimulations.
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From page 104... ...
1987. Vostok ice core: A continuous isotope temperature record over the last climatic cycle (160,000 years)
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From page 105... ...
1990. Little Ice Age (Neoglacial)
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From page 106... ...
1987. Earth's precession cycle and Quaternary climatic changes in tropical Africa.
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From page 107... ...
1987. Evidence of abrupt climatic change during the last 1,500 years recorded in ice cores from the tropical Quelccaya ice cap, Peru.
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