Climate in Earth History Studies in Geophysics (1982) / Chapter Skim
Currently Skimming:
2 Paleoclimatic Modeling--A Review with Reference to Problems and Prospects for the Pre-Pleistoncene
2 Paleoclimatic Modeling--A Review with Reference to Problems and Prospects for the Pre-Pleistoncene
Pages 26-42
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 26... ...
The systematic evaluation of model-simulated paleoclimates may also be expected to serve as a guide in the identification of the accuracy needed in paleoclimatic data and in the assembly and analysis of new data in regions of particular climatic significance. In view of the uncertainty that surrounds the global distribubon of many of the pre Pleistocene boundary condibons required by climate models, disagreement between the modeled and "observed" paleoclimate may be at least partly due to this source; experimentation with alternate but plausible distributions of mountains and shallow seas, for example, may improve the accuracy of both the simulated climate and
|
From page 27... ...
The purpose of this chapter is to review and evaluate climate modeling as a tool for paleoclimatic research. To this end, I shall first present an overview of the techniques and present status of climate modeling, followed by a brief review of past applications of climate models to paleoclimatology.
|
From page 28... ...
These latter elements respond relatively rapidly to atmospheric and oceanic conditions, while the former and more massive elements change much more slowly. In this respect the climate of the cryosphere is like that of the land surace and associated biornass, both of v hich contain elements of widely differing response times to the prevailing atmospheric (and oceanic)
|
From page 29... ...
For the most part the continental ice sheets which play such a large part in the geologic history of the Earth s surface have not been fu Iy incorporated into the interactive climate system nor have the longer-term changes of the land surface and biomass been adequately modeled. The dynamical basis of climate models rests on the fundamental equations that presumably govern the system s motion mass and energy together with whatever additional physical information is necessary to describe the system and its boundary conditions.
|
From page 30... ...
Similarly, for mode s of the ice sheets and land surface the necessary boundary conditions r=,/4 U,r,T~q -~-~/2- o- 2/4 U,v,T,qp,q :: . :\ sot /so t' 0 = 0 odel lop, p = ~~ - 200 my (' ~ 71> ; ~CL,: _ _ _ .
|
From page 31... ...
The climate models of lowest spatial resolution are those that effectively represent the entire atmosphere as a single point; those of highest spatial resolution are capable of resolving features of several-hundred-kilometer horizontal dimension and a few kilometer vertical dimension. Because the computational effort involved in solving a model generally varies as the cube of the spatial resolution, the higher-resolution models generally proceed relatively slowly on even the fastest of modern computers, whereas models of to s spatial resolution proceed hundreds or thousands of times faster.
|
From page 32... ...
Character istic .Uodel Perfo 7 mange To give a clear idea of the rlahlre and accuracy of the solution s to be expected from climate models, we first consider the characteristic performance of current atmospheric GCMs. The distribution of the average sea-level pressure simulated for the month of July in a recent integration of a two-level atmospheric GCM is shown in Figure 2.4, along with the observed climatological distribution (Schlesinger and Gates, 1979)
|
From page 33... ...
50. twos 30S 505 70 _ Ott BAD 70N ON ION sos ~ s 180 15OW 120W noteworthy in the case of precipitation, of which approximately half of that in mid-latitudes and nearly all of that in low latitudes is simulated to occur in association with convectivescale motions: the effective parameterization of this convective rainfall is one of the more difficult and sensitive aspects of climate modeling.
|
From page 34... ...
W LAWRENCE GATES mosphere in view of the close correspondence observed behheen the variations of sea-surface temperature and rainfall in the lower latitudes—a result of the surface temperature's control of surface evaporation and the subsequent convective condensation There is therefore an expectation that when these mechanisms are allowed to interact freely in a coupled oceanatmosphere GCM, there will be an improvement in at least the tropical simulatimt of both the sea-surface temperature and precipitation; the fact that this has not occurred to a marked degree in the few integrations of coupled GCMs that have been made so far is testimony to the difficulty of properly parameterizing the turbulent fluxes in the back-to-back atmospheric and oceanic surface-boundary layers and to the lack of an aderuate treatment of the disparate response times of the large scale atmospheric and oceanic circulation to these mutually determined surface fluxes.
|
From page 35... ...
From the viewpoint of climate modeling, paleoclimatic data serve two purposes: first, they are necessary for the realistic specification of the boundary conditions at the Earth's surface that are required by climate models, and, second, they are necessary for the verification of at least portions of the models' simulated climate As has been noted previously, the most demanding surface honorary conditions are those required by atmospheric GCMs; these consist of the location and elevation of the land surface relative to a possibly changed sea level, the sea-surface temperature, the distribution (and elevation) of ice sheets and sea ice, and the surface albedo, which serves to distinguish land-surface types and vegetative cover.
|
From page 36... ...
36 boot Vl _ to= o o c ·:: ,.
|
From page 37... ...
These data, representing conditions at the height of the Wisconsin ice age r bmlt 18,000 yr B P., include the global distribution of sea-surface temperature and sea ice fit ferred from the fossil record in deep-sea sediments) , the extent and thickness of ice sheets (reconstructed from glacial evidence and icesheet budgets)
|
From page 38... ...
. son 50N ens Zinc and SON 30~ 303 From the simulated July sea-level pressure shown in Figure 2.10, the major ioe-age change in the surface circulation is seen to be that associated with the semipermanent anticyclones found over the major ice sheets in North America and Europe this pattern implies a drastic change from the present characteristic July climate over the eastern and southern portions of these continents.
|
From page 39... ...
whose response time is intermediate between that of the ice sheets and the atmosphere, this strategy suggests that integration needs to be performed in response to a periodically updated atmospheric climate only over that time interval sufficient to generate a representative oceanic climate, with the land surface and ice sheets held fixed as boundary conditions; this interval is probably of the order of a few centuries. Finally, for the ice sheets themselves (and perhaps also for the land surface)
|
From page 40... ...
Explicit equilibrium Isnap-shot) resolution with new _ boundary conditions OCEAN FIXED FIXED FIXED 1 1 SEA ICE ICE SHEET LAND SURFACE ,,i,J Statistical resolution Equilibrium statistics transfer :)
|
From page 41... ...
Finally, it may be remarked that in the assembly of paleoclimatic proxy data for either model boundary conditions or verification particular attention should be given to the rapidly accumulating body of quantitative information from paleomagnetic, tectonic, and isotopic evidence, in addition to the use of the more qualitative climatic information from biogeographic souro s. Although there is always room for improvement, available models of She atmosphere and ocean are clearly capable of simulating the global structure of She currently observed seasonal climates wild acceptable accuracy, and the limited application that has been made of atmospheric models to the simulation of the Wisconsin ice-age climate has given encouraging resulLs.
|
From page 42... ...
. Report of the JOC Study Conference on Climate Models: Performance, Interoompari on and Sensitivity Studies, W
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.