共查询到20条相似文献,搜索用时 31 毫秒
1.
Claudia Kubatzki Martin Claussen Reinhard Calov Andrey Ganopolski 《Climate Dynamics》2006,27(4):333-344
We investigate the sensitivity of simulations of the last glacial inception (LGI) with respect to initial (size of the Greenland ice sheet) and surface (state of ocean/vegetation) conditions and two different CO2 reconstructions. Utilizing the CLIMBER-2 Earth system model, we obtain the following results: (a) ice-sheet expansion in North America at the end of the Eemian can be reduced or even completely suppressed when pre-industrial or Eemian ocean/vegetation is prescribed. (b) A warmer surrounding ocean and, in particular, a large Laurentide ice sheet reduce the size of the Greenland ice sheet before and during the LGI. (c) A changing ocean contributes much stronger to the expansion of the Laurentide ice sheet when we apply the CO2 reconstruction according to Barnola et al. (Nature 329:408–414, 1987) instead of Petit et al. (Nature 399:429–436, 1999). (d) In the fully coupled model, the CO2 reconstruction used has only a small impact on the simulated ice sheets but it does impact the course of the climatic variables. (e) For the Greenland ice sheet, two equilibrium states exist under the insolation and CO2 forcing at 128,000 years before present (128 kyear BP); the one with an ice sheet reduced by about one quarter as compared to its simulated pre-industrial size and the other with nearly no inland ice in Greenland. (f) Even the extreme assumption of no ice sheet in Greenland at the beginning of our transient simulations does not alter the simulated expansion of northern hemispheric ice sheets at the LGI. 相似文献
2.
This paper investigates the possible implications for the earth-system of a melting of the Greenland ice-sheet. Such a melting is a possible result of increased high latitude temperatures due to increasing anthropogenic greenhouse gas emissions. Using an atmosphere-ocean general circulation model (AOGCM), we investigate the effects of the removal of the ice sheet on atmospheric temperatures, circulation, and precipitation. We find that locally over Greenland, there is a warming associated directly with the altitude change in winter, and the altitude and albedo change in summer. Outside of Greenland, the largest signal is a cooling over the Barents sea in winter. We attribute this cooling to a decrease in poleward heat transport in the region due to changes to the time mean circulation and eddies, and interaction with sea-ice. The simulated climate is used to force a vegetation model and an ice-sheet model. We find that the Greenland climate in the absence of an ice sheet supports the growth of trees in southern Greenland, and grass in central Greenland. We find that the ice sheet is likely to regrow following a melting of the Greenland ice sheet, the subsequent rebound of its bedrock, and a return to present day atmospheric CO2 concentrations. This regrowth is due to the high altitude bedrock in eastern Greenland which allows the growth of glaciers which develop into an ice sheet. 相似文献
3.
Two climatic states and feedbacks on thermohaline circulation in an Earth system model of intermediate complexity 总被引:5,自引:0,他引:5
Zhaomin Wang 《Climate Dynamics》2005,25(2-3):299-314
The McGill Paleoclimate Model-2 (MPM-2) is employed to study climate–thermohaline circulation (THC) interactions in a pre
-industrial climate, with a special focus on the feedbacks on the THC from other climate system components. The MPM-2, a new
version of the MPM, has an extended model domain from 90S to 90N, active winds and no oceanic heat and freshwater flux adjustments.
In the MPM-2, there are mainly two stable modes for the Atlantic meridional overturning circulation (MOC) under the ‘present-day’
forcing (present-day solar forcing and the pre-industrial atmospheric CO2 level of 280 ppm). The ‘on’ mode has an active North Atlantic deep water formation, while the ‘off’ mode has no such deep
water formation. By comparing the ‘off’ mode climate state with its ‘on’ mode analogue, we find that there exist many large
differences between the two climate states, which originate from large changes in the oceanic meridional heat transports.
By suppressing or isolating each process associated with a continental ice sheet over North America, sea ice, the atmospheric
hydrological cycle and vegetation, feedbacks from these components on the Atlantic MOC are investigated. Sensitivity studies
investigating the role of varying continental ice growth and sea ice meridional transport in the resumption of the Atlantic
MOC are also carried out. The results show that a fast ice sheet growth and an enhanced southward sea ice transport significantly
favor the resumption of the Atlantic MOC in the MPM-2. In contrast to this, the feedback from the atmospheric hydrological
cycle is a weak positive one. The vegetation-albedo feedback could enhance continental ice sheet growth and thus could also
favor the resumption of the Atlantic MOC. However, before the shut-down of the Atlantic MOC, feedbacks from these components
on the Atlantic MOC are very weak. 相似文献
4.
S. J. Kim 《Climate Dynamics》2004,22(6-7):639-651
The role of reduced atmospheric CO2 concentration and ice sheet topography plus its associated land albedo on the LGM climate is investigated using a coupled atmosphere-ocean-sea ice climate system model. The surface cooling induced by the reduced CO2 concentration is larger than that by the ice sheet topography plus other factors by about 30% for the surface air temperature and by about 100% for the sea surface temperature. A large inter-hemispheric asymmetry in surface cooling with a larger cooling in the Northern Hemisphere is found for both cases. This asymmetric inter-hemispheric temperature response is consistent in the ice sheet topography case with earlier studies using an atmospheric model coupled with a mixed-layer ocean representation, but contrasts with these results in the reduced CO2 case. The incorporation of ocean dynamics presumably leads to a larger snow and sea ice feedback as a result of the reduction in northward ocean heat transport, mainly as a consequence of the decrease in the North Atlantic overturning circulation by the substantial freshening of the North Atlantic convection regions. A reversed case is found in the Southern Ocean. Overall, the reduction in atmospheric CO2 concentration accounts for about 60% of the total LGM climate change. 相似文献
5.
Timothy M. Lenton 《Climatic change》2006,76(1-2):7-29
Anthropogenic climate change will continue long after anthropogenic CO2 emissions cease. Atmospheric CO2, global warming and ocean circulation will approach equilibrium on the millennial timescale, whereas thermal expansion of
the ocean, ice sheet melt and their contributions to sea level rise are unlikely to be complete. Atmospheric CO2 in year 3000 depends non-linearly on the total amount of CO2 emitted and is very likely to exceed the present level of ∼380 ppmv. CO2 is doubled for ∼2500 GtC emitted, quadrupled if all ∼5000 GtC of conventional fossil fuel resources are emitted, and increases
by a factor of ∼32 if a further 20,000 GtC of exotic fossil fuel resources are emitted. Global warming in year 3000 will also
depend on climate sensitivity to doubling CO2, which is most probably ∼3 ∘C but highly uncertain. Thermal expansion will contribute 0.5–2 m to millennial sea level rise for each doubling of CO2. The Greenland ice sheet could melt completely within the millennium under > 8×CO2, adding a further ∼7 m to sea level. The rate of melt depends on the magnitude of forcing above a regional warming threshold
of 1–3 ∘C. The West Antarctic ice sheet could be threatened by 4–10 ∘C local warming, and its potential contribution to millennial sea level rise exceeds current maximum estimates of ∼1 m. The
fate of the ocean thermohaline circulation may depend on the rate as well as the magnitude of forcing. 相似文献
6.
Simulation of glacial-interglacial cycles by simple relaxation models: consistency with observational results 总被引:1,自引:0,他引:1
The model of Paillard and Parrenin (Earth Planet Sci Lett 227:263–271, 2004) was modified to obtain a closer fit to δ18O and CO2 time series for the last 800 kyr. The model performance can be improved if its CO2 sensitivity to I65 insolation is eliminated and if different response times are assumed for ablation/accumulation of ice. Correlations between simulated and experimental time series for CO2 and ice volume V increase from 0.59 and 0.63 to 0.79 and 0.88, respectively. According to these models, terminations are produced by I65 amplification through CO2-T and T-CO2 feedbacks, in synergy with an extra CO2 contribution from the deep ocean. This contribution is strongly dependent on ice-sheet extent and ice volume (or alternatively, CO2 concentration, which is a good proxy of Antarctic temperature) but is insensitive to Southern Ocean (SO) insolation on 21 February (I60). Change of deep SO state may be the “order parameter” for nonlinear deglacial changes. According to these models, 100 kyr periodicity of glacial cycles arises from the characteristic time of Antarctic ice sheet advance to the continental slope. 相似文献
7.
L. D. Danny Harvey 《Climatic change》2004,63(3):259-290
Carbon sequestration is increasingly being promoted as a potential response to the risks of unrestrained emissions of CO2, either in place of or as a complement to reductions in the use of fossil fuels. However, the potential role of carbon sequestration as an (at-least partial) substitute for reductions in fossil fuel use can be properly evaluated only in the context of a long-term acceptable limit (or range of limits) to the increase in atmospheric CO2 concentration, taking into account the response of the entire carbon cycle to artificial sequestration. Under highly stringent emission-reduction scenarios for non-CO2 greenhouse gases, 450 ppmv CO2 is the equivalent, in terms of radiative forcing of climate,to a doubling of the pre-industrial concentration of CO2. It is argued in this paper that compliance with the United Nations Framework Convention on Climate Change (henceforth, the UNFCCC) implies that atmospheric CO2 concentration should be limited, or quickly returned to, a concentration somewhere below 450 ppmv. A quasi-one-dimensional coupled climate-carbon cycle model is used to assess the response of the carbon cycle to idealized carbon sequestration scenarios. The impact on atmospheric CO2 concentration of sequestering a given amount of CO2 that would otherwise be emitted to the atmosphere, either in deep geological formations or in the deep ocean, rapidly decreases over time. This occurs as a result of a reduction in the rate of absorption of atmospheric CO2 by the natural carbon sinks (the terrestrial biosphere and oceans) in response to the slower buildup of atmospheric CO2 resulting from carbon sequestration. For 100 years of continuous carbon sequestration, the sequestration fraction (defined as the reduction in atmospheric CO2 divided by the cumulative sequestration) decreases to 14% 1000 years after the beginning of sequestration in geological formations with no leakage, and to 6% 1000 years after the beginning of sequestration in the deep oceans. The difference (8% of cumulative sequestration) is due to an eflux from the ocean to the atmosphere of some of the carbon injected into the deep ocean.The coupled climate-carbon cycle model is also used to assess the amount of sequestration needed to limit or return the atmospheric CO2 concentration to 350–400 ppmv after phasing out all use of fossil fuels by no later than 2100. Under such circumstances, sequestration of 1–2 Gt C/yr by the latter part of this century could limit the peak CO2 concentration to 420–460 ppmv, depending on how rapidly use of fossilfuels is terminated and the strength of positive climate-carbon cycle feedbacks. To draw down the atmospheric CO2 concentration requires creating negative emissions through sequestration of CO2 released as a byproduct of the production of gaseous fuels from biomass primary energy. Even if fossil fuel emissions fall to zero by 2100, it will be difficult to create a large enough negative emission using biomass energy to return atmospheric CO2 to 350 ppmv within 100 years of its peak. However, building up soil carbon could help in returning CO2 to 350 ppmv within 100 years of its peak. In any case, a 100-year period of climate corresponding to the equivalent of a doubled-CO2 concentration would occur before temperatures decreased. Nevertheless, returning the atmospheric CO2concentration to 350 ppmv would reduce longterm sea level rise due to thermal expansion and might be sufficient to prevent the irreversible total melting of the Greenland ice sheet, collapse of the West Antarctic ice sheet, and abrupt changes in ocean circulation that might otherwise occur given a prolonged doubled-CO2 climate. Recovery of coral reef ecosystems, if not already driven to extinction, could begin. 相似文献
8.
Glacial termination: sensitivity to orbital and CO2 forcing in a coupled climate system model 总被引:1,自引:0,他引:1
To study glacial termination and related feedback mechanisms, a continental ice dynamics model is globally and asynchronously
coupled to a physical climate (atmosphere-ocean-sea ice) model. The model performs well under present-day, 11 kaBP (thousand
years before present) and 21 kaBP perpetual forcing. To address the ice-sheet response under the effects of both perpetual
orbital and CO2 forcing, sensitivity experiments are conducted with two different orbital configurations (11 kaBP and 21 kaBP) and two different
atmospheric CO2 concentrations (200 ppmv and 280 ppmv). This study reveals that, although both orbital and CO2 forcing have an impact on ice-sheet maintenance and deglacial processes, and although neither acting alone is sufficient
to lead to complete deglaciation, orbital forcing seems to be more important. The CO2 forcing has a large impact on climate, not uniformly or zonally over the globe, but concentrated over the continents adjacent
to the North Atlantic. The effect of increased CO2 (from 200 ppmv to 280 ppmv) on surface air temperature has its peak there in winter associated with a reduction in sea-ice
extent in the northern North Atlantic. These changes are accompanied by an enhancement in the intensity of the meridional
overturning and poleward ocean heat transport in the North Atlantic. On the other hand, the effect of orbital forcing (from
21 kaBP to 11 kaBP) has its peak in summer. Since the summer temperature, rather than winter temperature, is found to be dominant
for the ice-sheet mass balance, orbital forcing has a larger effect than CO2 forcing in deglaciation. Warm winter sea surface temperature arising from increased CO2 during the deglaciation contributes to ice-sheet nourishment (negative feedback for ice-sheet retreat) through slightly enhanced
precipitation. However, the precipitation effect is totally overwhelmed by the temperature effect. Our results suggest that
the last deglaciation was initiated through increasing summer insolation with CO2 providing a powerful feedback.
Received: 22 February 2000 / Accepted: 17 September 2000 相似文献
9.
The future rate of Greenland Ice Sheet (GrIS) deglaciation and the future contribution of GrIS deglaciation to sea level rise will depend critically on the magnitude of northern hemispheric polar amplification and global equilibrium climate sensitivity. Here, these relationships are analyzed using an ensemble of multi-century coupled ice-sheet/climate model simulations seeded with observationally-constrained initial conditions and then integrated forward under tripled preindustrial CO2. Polar amplifications and climate sensitivities were varied between ensemble members in order to bracket current uncertainty in polar amplification and climate sensitivity. A large inter-ensemble spread in mean GrIS air temperature, albedo and surface mass balance trends stemming from this uncertainty resulted in GrIS ice volume loss ranging from 5 to 40 % of the original ice volume after 500 years. The large dependence of GrIS deglaciation on polar amplification and climate sensitivity that we find indicates that the representation of these processes in climate models will exert a strong control on any simulated predictions of multi-century GrIS evolution. Efforts to reduce polar amplification and equilibrium climate sensitivity uncertainty will therefore play a critical role in constraining projections of GrIS deglaciation and sea level rise in a future high-CO2 world. 相似文献
10.
A continuous simulation of global ice volume over the past 1 million years with 3-D ice-sheet models
B. de Boer R. S. W. van de Wal L. J. Lourens R. Bintanja T. J. Reerink 《Climate Dynamics》2013,41(5-6):1365-1384
Sea-level records show large glacial-interglacial changes over the past million years, which on these time scales are related to changes of ice volume on land. During the Pleistocene, sea-level changes induced by ice volume are largely caused by the waxing and waning of the large ice sheets in the Northern Hemisphere. However, the individual contributions of ice in the Northern and Southern Hemisphere are poorly constrained. In this study, for the first time a fully coupled system of four 3-D ice-sheet models is used, simulating glaciations on Eurasia, North America, Greenland and Antarctica. The ice-sheet models use a combination of the shallow ice and shelf approximations to determine sheet, shelf and sliding velocities. The framework consists of an inverse forward modelling approach to derive a self-consistent record of temperature and ice volume from deep-sea benthic δ18O data over the past 1 million years, a proxy for ice volume and temperature. It is shown that for both eustatic sea level and sea water δ18O changes, the Eurasian and North American ice sheets are responsible for the largest part of the variability. The combined contribution of the Antarctic and Greenland ice sheets is about 10 % for sea level and about 20 % for sea water δ18O during glacial maxima. However, changes in interglacials are mainly caused by melt of the Greenland and Antarctic ice sheets, with an average time lag of 4 kyr between melt and temperature. Furthermore, we have tested the separate response to changes in temperature and sea level for each ice sheet, indicating that ice volume can be significantly influenced by changes in eustatic sea level alone. Hence, showing the importance of a simultaneous simulation of all four ice sheets. This paper describes the first complete simulation of global ice-volume variations over the late Pleistocene with the possibility to model changes above and below present-day ice volume, constrained by observations of benthic δ18O proxy data. 相似文献
11.
Climate modification by future ice sheet changes and consequences for ice sheet mass balance 总被引:1,自引:1,他引:0
The future evolution of global ice sheets under anthropogenic greenhouse forcing and its impact on the climate system, including the regional climate of the ice sheets, are investigated with a comprehensive earth system model consisting of a coupled Atmosphere–Ocean General Circulation Model, a dynamic vegetation model and an ice sheet model. The simulated control climate is realistic enough to permit a direct coupling of the atmosphere and ice sheet components, avoiding the use of anomaly coupling, which represents a strong improvement with respect to previous modelling studies. Glacier ablation is calculated with an energy-balance scheme, a more physical approach than the commonly used degree-day method. Modifications of glacier mask, topographic height and freshwater fluxes by the ice sheets influence the atmosphere and ocean via dynamical and thermodynamical processes. Several simulations under idealized scenarios of greenhouse forcing have been performed, where the atmospheric carbon dioxide stabilizes at two and four times pre-industrial levels. The evolution of the climate system and the ice sheets in the simulations with interactive ice sheets is compared with the simulations with passively coupled ice sheets. For a four-times CO2 scenario forcing, a faster decay rate of the Greenland ice sheet is found in the non-interactive case, where melting rates are higher. This is caused by overestimation of the increase in near-surface temperature that follows the reduction in topographic height. In areas close to retreating margins, melting rates are stronger in the interactive case, due to changes in local albedo. Our results call for careful consideration of the feedbacks operating between ice sheets and climate after substantial decay of the ice sheets. 相似文献
12.
A climate model experiment was conducted using the HadCM3 climate model and a scenario in which the atmospheric CO2 concentration was increased over 70 years from pre-industrial concentrations to 4 times this level and then stabilised for
more than a 1,000 years. During the period of stabilisation the global atmospheric surface temperatures continued to rise
as the deep oceans adjusted towards a new equilibrium. However, even after 1,000 years this new equilibrium had not been reached.
During the first 600 years, Arctic and Antarctic winter sea ice thickness and area covered declined with a significant impact
on the global radiation budget. After this period the area of the Arctic covered by sea ice entered a 150 years period during
which time it underwent a series of oscillations. Following the oscillation the centre of the Arctic basin became ice free
throughout the year. A sensitivity experiment demonstrates that although the sea ice extent can be greatly reduced through
the artificial heating of the mixed layer, prior to the onset of the oscillatory phase the ice recovers over 15 years. Understanding
the causes of this oscillatory phase may elucidate the mechanisms of variability in the Arctic in the present climate and
in future policy relevant scenarios. We have investigated the atmospheric and oceanic forcing on the ice during the oscillatory
phase, and find that the behaviour is linked to a redistribution of Arctic Ocean heat stores. 相似文献
13.
On modelling the seasonal thermodynamic cycle of sea ice in studies of climatic change 总被引:1,自引:0,他引:1
Albert J. Semtner Jr. 《Climatic change》1984,6(1):27-37
Recent work in modelling climatic changes due to increased atmospheric CO2 has shown the maximum change to occur in the polar regions as a result of seasonal reductions in sea ice coverage. Typically, sea ice thermodynamics is modelled in a very simple way, whereby the storage of both sensible and latent heat within the ice is ignored, and the effects of snow cover on conductivity and on surface albedo and of oceanic heat flux on bottom ablation may also be neglected. This paper considers whether omission of these processes is justified within the context of quantitatively determining regional climatic changes. A related question, whether omission of ice dynamics can be justified, is not considered.Relatively complete one-dimensional models of sea-ice thermodynamics have previously been developed and tested for a variety of environmental conditions by Maykut and Untersteiner (1969, 1971) and by Semtner (1976). A simpler model which neglects the storage of sensible and latent heat is described in the Appendix to Semtner (1976). In that model, the errors in annual-mean ice thickness which would arise from neglect of heat storage can be compensated by increases in albedo and in conductivity. Here we examine the seasonal cycle of ice thickness predicted by such a model and find significant errors in phase (one month lead) and in amplitude (50% overestimate). The amplitude errors are enhanced as snowfall and oceanic heat flux diminish (or are neglected). This suggests that substantial errors may occur in climate simulations which use very simple formulations of sea ice thermodynamics, whereby early and excessive melting exaggerates the seasonal disappearance of sea ice.To illustrate the above point, two models are configured to examine the local response of Arctic sea ice to a quadrupling of atmospheric CO2. The first model neglects a number of physical processes and mimics the behavior of sea ice found in Manabe and Stouffer (1980), both for present and enhanced levels of CO2. The more complete second model gives a better simulation of Arctic ice for the present level of CO2 and shows a reduced response to CO2 quadrupling relative to that in Manabe and Stouffer (1980). In particular, the change in surface temperature is cut by a factor of two. In view of this result, a more complete treatment of sea ice thermodynamics would seem warranted in further studies of climate change. Only a minor computational increase is required.A portion of this study is supported by the U.S. Department of Energy as a part of its Carbon Dioxide Research Program.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
14.
T.M.L. Wigley 《Climatic change》2018,147(1-2):31-45
The Paris Agreement states that, relative to pre-industrial times, the increase in global average temperature should be kept to well below 2 °C and efforts should be made to limit the temperature increase to 1.5 °C. Emissions scenarios consistent with these targets are derived. For an eventual 2 °C warming target, this could be achieved even if CO2 emissions remained positive. For a 1.5 °C target, CO2 emissions could remain positive, but only if a substantial and long-lasting temperature overshoot is accepted. In both cases, a warming overshoot of 0.2 to 0.4 °C appears unavoidable. If the allowable (or unavoidable) overshoot is small, then negative emissions are almost certainly required for the 1.5 °C target, peaking at negative 1.3 GtC/year. In this scenario, temperature stabilization occurs, but cumulative emissions continue to increase, contrary to a common belief regarding the relationship between temperature and cumulative emissions. Changes to the Paris Agreement to accommodate the overshoot possibility are suggested. For sea level rise, tipping points that might lead to inevitable collapse of Antarctic ice sheets or shelves might be avoided for the 2 °C target (for major ice shelves) or for the 1.5 °C target for the West Antarctic Ice Sheet. Even with the 1.5 °C target, however, sea level will continue to rise at a substantial rate for centuries. 相似文献
15.
J. Oerlemans 《Climate Dynamics》2002,19(1):85-93
The total mass budget of the Antarctic ice sheet is studied with a simple axi-symmetrical model. The ice-sheet has a parabolic profile resting on a bed that slopes linearly downwards from the centre of the ice sheet into the ocean. The mean ice velocity at the grounding line is assumed to be proportional to the water depth. The accumulation rate is a linear function of the distance to the centre. Setting the total mass budget to zero yields a quadratic equation for the steady-state ice-sheet radius R. Analysis of the equilibrium states sheds light on the sensitivity of the ice-sheet radius to changes in sea level (S) and precipitation with respect to the present state (Prel). For model parameters obtained by matching the analytical model to the present state of the Antarctic ice sheet, the sensitivity values are dR/dS = -2400 and dR/dPrel = 4000 m/%. The model can also be used to study transient behaviour of the ice sheet. The characteristic relaxation time (e-folding time scale) is about 3500 years. Forcing the model with a sea-level and accumulation history over the past few hundred thousands of years yields Antarctic ice-volume curves that are similar to those obtained by comprehensive numerical modelling. The current imbalance predicted by the model corresponds to a sea-level rise of 0.25 mm yr-1. 相似文献
16.
Simulations of the Last Glacial Maximum climates using a general circulation model: prescribed versus computed sea surface temperatures 总被引:2,自引:0,他引:2
The climate during the Last Glacial Maximum (LGM) has been simulated using the UK Universities Global Atmospheric Modelling
Programme (UGAMP) general circulation model (GCM) with both prescribed sea surface temperatures (SSTs) based on the CLIMAP
reconstruction and computed SSTs with a simple thermodynamic slab ocean. Consistent with the Paleoclimate Modelling Intercomparison
Project (PMIP), the other boundary conditions include the large changes in ice-sheet topography and geography, a lower sea
level, a lower concentration of CO2 in the atmosphere, and a slightly different insolation pattern at the top of the atmosphere. The results are analysed in
terms of changes in atmospheric circulation. Emphasis is given to the changes in surface temperatures, planetary waves, storm
tracks and the associated changes in distribution of precipitation. The model responds in a similar manner to the changes
in boundary conditions to previous studies in global mean statistics, but differs in its treatment of regional climates. Results
also suggest that both the land ice sheets and sea ice introduce significant changes in planetary waves and transient eddy
activity, which in turn affect regional climates. The computed SST simulations predict less sea ice and cooler tropical temperatures
than those based on CLIMAP SSTs. It is unclear as to whether this is a model and/or a data problem, but the resulting changes
in land temperatures and precipitation can be large. Snow mass budget analysis suggests that there is net ice loss along the
southern edges of the Laurentide and Fennoscandian ice sheets and net ice gain over other parts of the two ice sheets. The
net accumulation is mainly due to the decrease in ablation in the cold climate rather than to the changes in snowfall. The
characteristics of the Greenland ice-sheet mass balance in the LGM simulations is also quite different from those in the present-day
(PD) simulations. The ablation in the LGM simulations is negligible while it is a very important process in the ice mass budget
in the PD simulations.
Received: 10 January 1997 / Accepted: 11 December 1997 相似文献
17.
Past and future polar amplification of climate change: climate model intercomparisons and ice-core constraints 总被引:2,自引:2,他引:2
V. Masson-Delmotte M. Kageyama P. Braconnot S. Charbit G. Krinner C. Ritz E. Guilyardi J. Jouzel A. Abe-Ouchi M. Crucifix R. M. Gladstone C. D. Hewitt A. Kitoh A. N. LeGrande O. Marti U. Merkel T. Motoi R. Ohgaito B. Otto-Bliesner W. R. Peltier I. Ross P. J. Valdes G. Vettoretti S. L. Weber F. Wolk Y. YU 《Climate Dynamics》2006,26(5):513-529
Climate model simulations available from the PMIP1, PMIP2 and CMIP (IPCC-AR4) intercomparison projects for past and future
climate change simulations are examined in terms of polar temperature changes in comparison to global temperature changes
and with respect to pre-industrial reference simulations. For the mid-Holocene (MH, 6,000 years ago), the models are forced
by changes in the Earth’s orbital parameters. The MH PMIP1 atmosphere-only simulations conducted with sea surface temperatures
fixed to modern conditions show no MH consistent response for the poles, whereas the new PMIP2 coupled atmosphere–ocean climate
models systematically simulate a significant MH warming both for Greenland (but smaller than ice-core based estimates) and
Antarctica (consistent with the range of ice-core based range). In both PMIP1 and PMIP2, the MH annual mean changes in global
temperature are negligible, consistent with the MH orbital forcing. The simulated last glacial maximum (LGM, 21,000 years
ago) to pre-industrial change in global mean temperature ranges between 3 and 7°C in PMIP1 and PMIP2 model runs, similar to
the range of temperature change expected from a quadrupling of atmospheric CO2 concentrations in the CMIP simulations. Both LGM and future climate simulations are associated with a polar amplification
of climate change. The range of glacial polar amplification in Greenland is strongly dependent on the ice sheet elevation
changes prescribed to the climate models. All PMIP2 simulations systematically underestimate the reconstructed glacial–interglacial
Greenland temperature change, while some of the simulations do capture the reconstructed glacial–interglacial Antarctic temperature
change. Uncertainties in the prescribed central ice cap elevation cannot account for the temperature change underestimation
by climate models. The variety of climate model sensitivities enables the exploration of the relative changes in polar temperature
with respect to changes in global temperatures. Simulated changes of polar temperatures are strongly related to changes in
simulated global temperatures for both future and LGM climates, confirming that ice-core-based reconstructions provide quantitative
insights on global climate changes.
An erratum to this article can be found at 相似文献
18.
A simple climate model has been developed to investigate the existence of the small ice cap instability in the Southern Hemisphere.
The model consists of four coupled components: an atmospheric energy balance model, a thermodynamic snow-sea ice model, an
oceanic mixed layer model and a terrestrial ice model. Results from a series of experiments involving different degrees of
coupling in the model show that the instability appears only in those cases when an explicit representation of the Antarctic
ice sheet is not included in the model. In order to determine which physical processes in the ice sheet model lead to a stabilization
of the system we have conducted several sensitivity experiments in each of which a given ice sheet process has been removed
from the control formulation of the model. Results from these experiments suggest that the feedback between the elevation
of the ice sheet and the snow accumulation-ice ablation balance is responsible for the disappearance of the small ice cap
instability in our simulation. In the model, the mass balance of the ice sheet depends on the air temperature at sea level
corrected for altitude and it is, therefore, a function of surface elevation. This altitude-mass balance feedback effectively
decouples the location of the ice edge from any specific sea level isotherm, thus decreasing the model sensitivity to the
albedo-temperature feedback, which is responsible for the appearance of the instability. It is also shown that the elevation-radiative
cooling feedback tends to stabilize the ice sheet, although its effect does not seem to be strong enough to remove the instability.
Another interesting result is that for those simulations which include the terrestrial ice model with elevation-dependent
surface mass balance, hysteresis is exhibited, where for a given level of external forcing, two stable solutions with different,
non-zero ice-sheet volume and area and different air and ocean temperature fields occur. However, no unstable transition between
the two solutions is ever observed. Our results suggest that the small ice cap instability mechanism could be unsuitable for
explaining the inception of glaciation in Antarctica.
Received: 14 April 1997 / Accepted: 22 October 1997 相似文献
19.
Responses of ocean circulation and ocean carbon cycle in the course of a global glaciation from the present Earth conditions are investigated by using a coupled climate-biogeochemical model. We investigate steady states of the climate system under colder conditions induced by a reduction of solar constant from the present condition. A globally ice-covered solution is obtained under the solar constant of 92.2% of the present value. We found that because almost all of sea water reaches the frozen point, the ocean stratification is maintained not by temperature but by salinity just before the global glaciation (at the solar constant of 92.3%). It is demonstrated that the ocean circulation is driven not by the surface cooling but by the surface freshwater forcing associated with formation and melting of sea ice. As a result, the deep ocean is ventilated exclusively by deep water formation in southern high latitudes where sea ice production takes place much more massively than northern high latitudes. We also found that atmospheric CO2 concentration decreases through the ocean carbon cycle. This reduction is explained primarily by an increase of solubility of CO2 due to a decrease of sea surface temperature, whereas the export production weakens by 30% just before the global glaciation. In order to investigate the conditions for the atmospheric CO2 reduction to cause global glaciations, we also conduct a series of simulations in which the total amount of carbon in the atmosphere?Cocean system is reduced from the present condition. Under the present solar constant, the results show that the global glaciation takes place when the total carbon decreases to be 70% of the present-day value. Just before the glaciation, weathering rate becomes very small (almost 10% of the present value) and the organic carbon burial declines due to weakened biological productivity. Therefore, outgoing carbon flux from the atmosphere?Cocean system significantly decreases. This suggests the atmosphere?Cocean system has strong negative feedback loops against decline of the total carbon content. The results obtained here imply that some processes outside the atmosphere?Cocean feedback loops may be required to cause global glaciations. 相似文献
20.
Application of an ice sheet model developed for the Pleistocene to the extensive Carboniferous glaciation on Gondwana yields
an ice sheet which has several features consistent with observations. While complete deglaciation is not achieved without
CO2 changes, the Milankovich-induced fluctuations in ice sheet volume are comparable to Pleistocene glacial/ interglacial signals.
This result is shown to hold for a large fraction of physically reasonable parameter space. The model also exhibits multiple
equilibria and sharp bifurcations, as infinitesimal changes in the solar constant or precipitation can lead to a qualitatively
different climate. The success of the model in predicting ice location in an environment quite different from the Pleistocene
provides additional support for the robustness of the basic model physics and suggests that the model can be applied with
some confidence to other pre-Pleistocene glaciations.
Received: 30 June 1998 / Accepted: 5 January 1999 相似文献