Decade-to-Century-Scale Climate Variability and Change A Science Strategy (1998) / Chapter Skim
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4 Mechanisms and Predictability
4 Mechanisms and Predictability
Pages 39-47
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From page 39... ...
The boundary conditions for an atmospheric model (in particular SST and land and sea ice) are specified, and the atmospheric circulation and hydrologic cycle are allowed to come into equilibrium with these specifications.
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From page 40... ...
Medium-range climate prediction, prediction on time scales of a decade or so, is the most problematic type of prediction. Its value as uninitialized prediction is limited: The year-to-year variability of climate, together with the relatively slow approach of the climate system to equilibrium with anthropogenically added radiatively active atmospheric constituents, limit the value of prediction of the statistics of boundary conditions a decade in advance.
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From page 41... ...
We can distinguish two basic types of mechanisms for decadal variability: variability forced by processes external to the climate system, and variability generated by processes internal to the climate system. Externally Forced Atmospheric Variability In the external-forcing category are forcings by varying solar output; by addition of aerosols due to major volcanic eruptions, biomass burning, and industrial sources; and by the addition of radiatively active gases to the atmosphere.
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From page 42... ...
Recently, Latif and Barnett (1996) have suggested a mechanism by which coupling between the atmosphere and upper ocean that takes place in the mid-latitude North Pacific basin may give rise to climate variability in the North Pacific and North America on the multidecadal time scale.
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From page 43... ...
ENSO on shorter time scales is an example of this; the initial state is the thermocline's configuration, which, when specified at the initial time, determines the future evolution of the upper tropical ocean and hence its temperature structure. This kind of prediction also seems to work for the modal structures involved with the Atlantic subtropical dipole (Chang et al., 1998)
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From page 44... ...
A decrease in soil moisture has a feedback effect that increases surface temperature, as does reduced evapotranspiration by vegetation. Believable early warning of a prolonged period of increased temperature and decreased precipitation, especially in the prime agricultural lands of the Northern Hemisphere, would provide opportunities to avert global food insecurity and attendant disruptions: Irrigation infrastructure could be built, markets could be stabilized by futures hedging, drought-resistant seed could be stocked, and so on.
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From page 45... ...
This section deals with uninitialized prediction on interdecadal time scales, and in particular the response of climate to the anthropogenic addition of radiatively active constituents (gases and aerosols) to the atmosphere.
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From page 46... ...
Local changes in land level can result from altered sedimentation rates, or from subsidence due to extraction of groundwater or oil. Sea level is also subject to local changes forced by local winds, river runoff, and the passage of oceanic waves of various frequencies.
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From page 47... ...
47 sponse of terrestrial carbon sinks to altered climate or to anthropogenic inputs, for instance, or the effects of largescale, vegetation-related albedo or surface roughness changes on climate. As longer time series of the relevant vegetation data become available for testing ecosystem-climate models, and these models are more rigorously validated and improved, the value of their forecasts will increase, particularly to the societies and institutions that depend most directly on ecosystems.
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