Toward an Understanding of Global Change Initial Priorities for U.S. Contributions to the International Geosphere - Biosphere Program (1988) / Chapter Skim
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Climatic and Hydrologic Systems
Climatic and Hydrologic Systems
Pages 107-133
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From page 107... ...
The atmospheric concentrations of CO2, CH4, and other important trace gases are maintained by biogeochemical cycles. Warming from an increase in radiative forcing, promoted by human activities, will alter the global distribution of temperature and moisture on time scales of at least decades to centuries and possibly over much A draft of this paper was prepared by committee member Robert Dickinson and revised according to comments received from a wide range of scientists (see the appendix to this paper)
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From page 108... ...
The figure allows for emissions of all the trace gases affecting climate and for the clelay of global temperature increase resulting from oceanic heat uptake. A narrowing in the uncertainty of the global average changes in the climate system is obviously needed.
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From page 109... ...
109 LU I 4 ~ 3 CC LU CL LL cc 1 m o o j 1 1 Upper Scenario (rate 0.8 C/decade) \~/ Middle Scenario / (rate 0.30C/decade)
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From page 110... ...
Episodic astronomical events such as collisions with large asteroids are very rare in the earth's history, but when they occur they can have drastic effects. With respect to individual processes, it may be convenient to regard also as external forcing the radiative effects of atmospheric constituents as well as those modifications of the land surface that change so slowly that they can be considered only weakly coupled to the climate system on the decadal time scale.
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From page 111... ...
Monitoring these aerosol clouds and documenting the climatic response can help the interpretation of trends in surface temperatures and contribute to an understanding of atmospheric transport properties. Individual large eruptions that have occurred since the beginning of the availability of global temperature records are known to have decreased global mean temperature by as much as 1°C for up to a few years.
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From page 112... ...
Tectonic, Geothermal, Isostatic Rebound, Geomorphological, and Soil Changes Tectonic modifications of continental positions and shapes on 10million-year time scales are implicated in very large climatic changes. Past variations of tectonic and volcanic factors may help test our understanding of the climatic response to large forcing, both as a surrogate verification of climate model performance and for understanding sea level changes and their potential climatic connections.
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From page 113... ...
Since the atmospheric lifetime of CH4 (about 10 years) is short in comparison with the time scale of changes in its concentration, shifts in its concentration reflect changes in the balance between sources
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From page 114... ...
Lifetimes of aerosols depend on wet and dry deposition processes, which may vary with climate change. Other Trace Gases The CFCs Fell and F-12 may in several decades also build up to large enough concentrations to add significantly to greenhouse warming.
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From page 115... ...
The issue of realistically modeling how land processes, in particular vegetation and soil moisture, interact with the climate system is only now beginning to be addressed. Such modeling should recognize the two-way coupling between these two systems, as vegetation changes both its form and its function in response to climatic forcing.
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From page 116... ...
Some differences occur in the vertical, latitudinal, and seasonal distribution of atmospheric radiative forcing, but the effects of these differences are not yet established and are apparently relatively small. Thus studies of the global response of climate to increases in atmospheric CO2 also largely apply to increases of other trace gases and to increased solar heating.
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From page 117... ...
Different GCM simulations have shown qualitatively similar spatial patterns in the TongitudinaDy averaged cloudiness change; they indicate, in particular, a decrease in cloudiness in the moist, connectively active regions such as the tropical and midcIle latitude rain belt and an increase in the stable region near the surface from micIdle to high latitudes as wed as in the Tower stratosphere. Such cloud changes would be expected to have significant regional effects on radiative balance and hence surface temperature.
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From page 118... ...
Treatments of these issues have been handicapped by inadequate consideration of the complex effects of sea ice dynamics, ice distributions at subgrid scale, and interactions with ocean dynamics and salinity and with overlying cloud cover. Also, polar regions, especially in winter, are relatively poorly represented by global climate models because of their low absolute concentrations of water vapor and the singular aspects of the poles in spherical coordinate systems.
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From page 119... ...
At the low horizontal resolution of current global models, the simulations of sharp features such as the tropical rain belts and frontal systems are smoothed. The orographic effects of mountains and ice sheets are poorly treated.
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From page 120... ...
Climate models that are used to simulate future climate change from increasing trace gases have not yet incorporated detailed models of hydrological processes. However, simple energy- and moistureconserving parameterizations for soil moisture have resulted in an indication of possible future hydrological change.
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From page 121... ...
Oceanic heat uptake will affect the transient evolution of both global temperature increase and changes in regional hydrological properties. In high latitudes, the presence and seasonal variation of sea ice constitute another important oceanic climate factor that couples to atmospheric and oceanic energy exchange processes and can substantially enhance the response of high-latitude climate to radiative forcing.
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From page 122... ...
Abrupt transitions between these modes might be triggered by variations in salinity of the high-latitude oceans caused by changes in river flow, glacial melt water, sea level, precipitation, or evaporation. Other features of oceanic circulation, which in turn strongly affect the rest of the system, may shift abruptly in response to slow shifts in atmospheric circulation and rainfall patterns.
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From page 123... ...
D O CUMENTATION OF PRES ENT CLIMATE AND THE FACTORS THAT CAUSE IT TO CHANGE The following key research issues should be addressed: i 1. The recovery of the past history of environmental change, evolving studies of ocean and lake sediments, ice cores, tree rings, and sea level changes for information about past climate, hydrological regimes, ocean circulation, biological interaction, atmospheric chemical composition, and solar inputs.
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From page 124... ...
; and (3) significant uncertainties in the three-dimensional global distribution of water vapor and clouds, and the almost total lack of global information about surface properties, including soil moisture.
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From page 125... ...
Radiative balance of the climate system, and the dynamical processes that give rise to cloudiness, are highly significant for climate. Continuous measurements of the total solar output provide a fundamental boundary condition for radiative inputs, as do measurements of the varying contribution to planetary albedo from stratospheric aerosols.
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From page 126... ...
A detailed description of surface-energy balance over land, like that over the ocean, requires both atmospheric and surface information. Observational research on land surface climate processes and hydrology must be closely coordinated with related meteorological studies, such as those of the U.S.
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From page 127... ...
Complementing the sparse data coverage by the many shipbased programs, satellites provide regular global observations over the ocean of surface temperatures, sea ice cover, and in the future, wind stress from roughness, winds over the ocean, and sea level height. It is necessary to measure the geoid more accurately in order to use sea level heights to derive ocean surface currents.
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From page 128... ...
These properties include precipitation, measures of soil moisture, and vegetation cover, all on a regional scale. Measurements must include the surface radiative temperature, incident solar flux, seasonal snow cover, snow water equivalent, changes in the volume of high-altitude and continental ice sheets, amount of river runoff, distribution of permafrost, levels and freezing dates of lakes, extent and seasonaTity of wetlands, and other surface characteristics such as albedo, roughness, and emissivities in the infrared and microwave bands.
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From page 129... ...
* F Ocean Variables: Sea-surface temperature Seance extent Sea-ice type Sea-ice motion Ocean wind stress Sea level Incident solar flux Subsurface circulation Ocean chlorophyll Biogeochemical fluxes Ocean CO,, B D CC D D CCC C Land-Surtace Properties: Surface radiating temperature *
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From page 130... ...
In particular the dynamics of terrestrial vegetation, through its dependence on water supply from precipitation, are linked to climate. Current information on the global and regional budgets of water is inadequate, and key ingredients i.e., clouds, atmospheric water vapor, soil moisture, precipitation, and evaporation are now inadequately measured.
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From page 131... ...
These factors are still poorly represented in global climate models. They depend in part on the changes of vegetation cover with seasonal temperatures and associated extreme weather events, and on variations in precipitation processes, seasonal or otherwise.
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From page 132... ...
1988. National Climate Program Five Year Plan 1988-1992.
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From page 133... ...
Paw U University of California, Davis Veerabhadran Ramanathan, University of Chicago CIaes Rooth, University of Miami Jorge Sarmiento, Geophysics Fluid Dynamics Laboratory Stephen Schneider, National Center for Atmospheric Research Piers SeDers, NASA Goddard Space Flight Center Kevin Trenberth, National Center for Atmospheric Research Tom Van der Haar, Colorado State University J
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