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1.
A version of the National Center for Atmospheric Research community climate model — a global, spectral (R15) general circulation model — is coupled to a coarse-grid (5° latitude-] longitude, four-layer) ocean general circulation model to study the response of the climate system to increases of atmospheric carbon dioxide (CO2). Three simulations are run: one with an instantaneous doubling of atmospheric CO2 (from 330 to 660 ppm), another with the CO2 concentration starting at 330 ppm and increasing linearly at a rate of 1% per year, and a third with CO2 held constant at 330 pm. Results at the end of 30 years of simulation indicate a globally averaged surface air temperature increase of 1.6° C for the instantaneous doubling case and 0.7°C for the transient forcing case. Inherent characteristics of the coarse-grid ocean model flow sea-surface temperatures (SSTs) in the tropics and higher-than-observed SSTs and reduced sea-ice extent at higher latitudes] produce lower sensitivity in this model after 30 years than in earlier simulations with the same atmosphere coupled to a 50-m, slab-ocean mixed layer. Within the limitations of the simulated meridional overturning, the thermohaline circulation weakens in the coupled model with doubled CO2 as the high-latitude ocean-surface layer warms and freshens and westerly wind stress is decreased. In the transient forcing case with slowly increasing CO2 (30% increase after 30 years), the zonal mean warming of the ocean is most evident in the surface layer near 30°–50° S. Geographical plots of surface air temperature change in the transient case show patterns of regional climate anomalies that differ from those in the instantaneous CO2 doubling case, particularly in the North Atlantic and northern European regions. This suggests that differences in CO2 forcing in the climate system are important in CO2 response in regard to time-dependent climate anomaly regimes. This confirms earlier studies with simple climate models that instantaneous CO2 doubling simulations may not be analogous in all respects to simulations with slowly increasing CO2.A portion of this study is supported by the US Department of Energy as part of its Carbon Dioxide Research Program 相似文献
2.
Quantifying contributions to polar warming amplification in an idealized coupled general circulation model 总被引：2，自引：1，他引：1
An idealized coupled general circulation model is used to demonstrate that the surface warming due to the doubling of CO2 can still be stronger in high latitudes than in low latitudes even without the negative evaporation feedback in low latitudes
and positive ice-albedo feedback in high latitudes, as well as without the poleward latent heat transport. The new climate
feedback analysis method formulated in Lu and Cai (Clim Dyn 32:873–885, 2009) is used to isolate contributions from both radiative and non-radiative feedback processes to the total temperature change
obtained with the coupled GCM. These partial temperature changes are additive and their sum is convergent to the total temperature
change. The radiative energy flux perturbations due to the doubling of CO2 and water vapor feedback lead to a stronger warming in low latitudes than in high latitudes at the surface and throughout
the entire troposphere. In the vertical, the temperature changes due to the doubling of CO2 and water vapor feedback are maximum near the surface and decrease with height at all latitudes. The simultaneous warming
reduction in low latitudes and amplification in high latitudes by the enhanced poleward dry static energy transport reverses
the poleward decreasing warming pattern at the surface and in the lower troposphere, but it is not able to do so in the upper
troposphere. The enhanced vertical moist convection in the tropics acts to amplify the warming in the upper troposphere at
an expense of reducing the warming in the lower troposphere and surface warming in the tropics. As a result, the final warming
pattern shows the co-existence of a reduction of the meridional temperature gradient at the surface and in the lower troposphere
with an increase of the meridional temperature gradient in the upper troposphere. In the tropics, the total warming in the
upper troposphere is stronger than the surface warming. 相似文献
3.
To investigate the hydrologic changes of climate in response to an increase of CO2-concentration in the atmosphere, the results from numerical experiments with three climate models are analyzed and compared
with each other. All three models consist of an atmospheric general circulation model and a simple mixed layer ocean with
a horizontally uniform heat capacity. The first model has a limited computational domain and simple geography with a flat
land surface. The second model has a global computational domain with realistic geography. The third model is identical to
the second model except that it has a higher computational resolution. In each numerical experiment, the CO2-induced change of climate is evaluated based upon a comparison between the two climates of a model with normal and four times
the normal concentration of carbon dioxide in air.
It is noted that the zonal mean value of soil moisture in summer reduces significantly in two separate zones of middle and
high latitudes in response to the increase of the CO2-concentration in air. This CO2-induced summer dryness results not only from the earlier ending of the snowmelt season, but also from the earlier occurrence
of the spring to summer reduction in rainfall rate. The former effect is particularly important in high latitudes, whereas
the latter effect becomes important in middle latitudes. Other statistically significant changes include large increases in
both soil moisture and runoff rate in high latitudes of a model during most of the annual cycle with the exception of the
summer season. The penetration of moisture-rich, warm air into high latitudes is responsible for these increases. 相似文献
4.
Garth Paltridge Albert Arking Michael Pook 《Theoretical and Applied Climatology》2009,98(3-4):351-359
The National Centers for Environmental Prediction (NCEP) reanalysis data on tropospheric humidity are examined for the period 1973 to 2007. It is accepted that radiosonde-derived humidity data must be treated with great caution, particularly at altitudes above the 500 hPa pressure level. With that caveat, the face-value 35-year trend in zonal-average annual-average specific humidity q is significantly negative at all altitudes above 850 hPa (roughly the top of the convective boundary layer) in the tropics and southern midlatitudes and at altitudes above 600 hPa in the northern midlatitudes. It is significantly positive below 850 hPa in all three zones, as might be expected in a mixed layer with rising temperatures over a moist surface. The results are qualitatively consistent with trends in NCEP atmospheric temperatures (which must also be treated with great caution) that show an increase in the stability of the convective boundary layer as the global temperature has risen over the period. The upper-level negative trends in q are inconsistent with climate-model calculations and are largely (but not completely) inconsistent with satellite data. Water vapor feedback in climate models is positive mainly because of their roughly constant relative humidity (i.e., increasing q) in the mid-to-upper troposphere as the planet warms. Negative trends in q as found in the NCEP data would imply that long-term water vapor feedback is negative—that it would reduce rather than amplify the response of the climate system to external forcing such as that from increasing atmospheric CO2. In this context, it is important to establish what (if any) aspects of the observed trends survive detailed examination of the impact of past changes of radiosonde instrumentation and protocol within the various international networks. 相似文献
5.
Results from a global coupled ocean-atmosphere general circulation model (GCM) are used to perform the first in a series of studies of the various time and space scales of climate anomalies in an environment of gradually increasing carbon dioxide (CO2) (a linear transient increase of 1% per year in the coupled model). Since observed climate anomaly patterns often are computed as time-averaged differences between two periods, climate-change signals in the coupled model are defined using differences of various averaging intervals between the transient and control integrations. Annual mean surface air temperature differences for several regions show that the Northern Hemisphere warms faster than the Southern Hemisphere and that land areas warm faster than ocean. The high northern latitudes outside the North Atlantic contribute most to global warming but also exhibit great variability, while the high southern latitudes contribute the least. The equatorial tropics warm more slowly than the subtropics due to strong upwelling and mixing in the ocean. The globally averaged surface air temperature trend computed from annual mean differences for years 23–60 is 0.03 C per year. Projecting this trend to the time of CO2 doubling in year 100 produces a warming of 2.3° C. By chance, one particular northern winter five-year average geographical difference pattern in the Northern Hemisphere from the coupled model resembles the recent observed pattern of surface temperature and sea-level pressure anomalies. This pattern is not consistent from one five-year period to the next in any season in the model. However, multidecadal averages in the coupled model show that the North Atlantic warms less than the rest of the high northern latitudes, and recent observations may be a manifestation of this phenomenon. Consistent geographic patterns of climate anomalies forced by increased CO2 in the model are more evident with a longer averaging interval. There is also the possibility that the CO2 climate-change signal may itself be a function of time and space. The general pattern of zonal mean temperature anomalies for all periods in the model shows warming in the troposphere and cooling in the stratosphere. This pattern (or one similar to it taking into account the rest of the trace gases) could be looked for in observations to verify the enhanced greenhouse effect. A zonal mean pattern, however, could prove scientifically satisfactory but of little value to policymakers seeking regional climate-change forecasts. These results from the coupled model underscore the difficulty in identifying a time- and space-dependent fingerprint of greenhouse warming that has some practical use from short climatic records and point to the need to understand the mechanisms of decadal-scale variability.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
6.
The broad-scale distribution of terrestrial ecosystem complexes is determined in large part by climate and can be altered by climatic change due to natural causes or due to human activities such as those leading to increasing atmospheric CO2 concentration. Classifications that recognize the dependence of natural vegetation on climate provide one means of constructing maps to display the impact of climatic change on the geography of major vegetation zones. A world map of the Holdridge Life-Zone Classification, developed from approximately 8,000 meteorological records, is compared with a Holdridge Map with average temperature increments simulated by a. model of climate under elevated atmospheric CO2 concentration. The largest changes are indicated at high latitudes, where the simulated temperature increase is largest and the temperature intervals defining life zones are smallest. Boreal Forest Zones are replaced by either Cool Temperate Forest or Cool Temperate Steppe, depending on average precipitation. Changes in the tropics are smaller; however, in some regions, Subtropical Moist Forest is replaced by Tropical Dry Forest.Research supported by the National Science Foundation's Ecosystem Studies Program under Interagency Agreement Nos. DEB81-15316 and DEB83-15185. 相似文献
7.
《大气与海洋》2013,51(3):224-237
Abstract The University of Victoria's (UVic) Earth System Climate model is used to conduct equilibrium atmospheric CO2 sensitivity experiments over the range 200–1600 ppm in order to explore changes in northern hemisphere snow cover and feedbacks on terrestrial surface air temperature (SAT). Simulations of warmer climates predict a retreat of snow cover over northern continents, in a northeasterly direction. The decline in northern hemisphere global snow mass is estimated to reach 33% at 600 ppm and 54% at 1200 ppm. In the most northerly regions, annual mean snow depth increases for simulations with CO2 levels higher than present day. The shift in the latitude of maximum snowfall is estimated to be inversely proportional to the CO2 concentration. The northern hemisphere net shortwave radiation changes are found to be greater over land than over the ocean, suggesting a stronger albedo feedback from changes in terrestrial snow cover than from changes in sea ice. Results also reveal high sensitivity of the snow mass balance under low CO2 conditions. The amplification feedback (defined as the zonal SAT anomaly caused by doubling CO2 divided by the equatorial anomaly) is greatest for scenarios with less than 300 ppm, reaching 1.9 at the pole for 250 ppm. The stronger feedback is attributed to the significant albedo changes over land areas. The simulation with 200 ppm triggers continuous accumulation of snow ('glaciation') in regions which, according to paleo‐reconstructions, were covered by ice during the last glacial cycle (the Canadian Arctic, Scandinavia, and the Taymir Peninsula). 相似文献
8.
The multi-component “green” McGill Paleoclimate Model (MPM), which includes interactive vegetation, is used to simulate the
next glacial inception under orbital and prescribed atmospheric CO2 forcing. This intermediate complexity model is first run for short-term periods with an increasing atmospheric CO2 concentration; the model's response is in general agreement with the results of GCMs for CO2 doubling. The green MPM is then used to derive projections of the climate for the next 100 kyr. Under a constant CO2 level, the model produces three types of evolution for the ice volume: an imminent glacial inception (low CO2 levels), a glacial inception in 50 kyr (CO2 levels of 280 or 290 ppm), or no glacial inception during the next 100 kyr (CO2 levels of 300 ppm and higher). This high sensitivity to the CO2 level is due to the exceptionally weak future variations of the summer insolation at high northern latitudes. The changes
in vegetation re-inforce the buildup of ice sheets after glacial inception. Finally, if an initial global warming episode
of finite duration is included, after which the atmospheric CO2 level is assumed to stabilize at 280, 290 or 300 ppm, the impact of this warming is seen only in the first 5 kyr of the run;
after this time the response is insensitive to the early warming perturbation. 相似文献
9.
J. Syktus J. Chappell R. Oglesby J. Larson S. Marshall B. Saltzman 《Climate Dynamics》1997,13(5):293-302
Detection of an enhanced greenhouse effect on climate depends on recognition of a signal of change amidst the combined noise
of climatic variability and uncertainty in the nature of the signal (functional response to changing CO2). Using two different GCMs (one with a coupled dynamic upper ocean) and an ensemble of 20 equilibrium experiments with CO2 ranging from 100 to 3500 ppm, we find that that two measures of signal-to-noise (S/N) for the response of surface temperature
to CO2 forcing are larger over tropical and subtropical oceans than over low-latitude landmasses and larger than at higher latitudes
generally. One S/N measure has the noise based solely on inherent model variability, while the other S/N measure includes
both this variability and a measure of the uncertainty in the functional nature of the signal. Although the experiments were
not for transient forcing and sulphate aerosols and other potentially important forcings (e.g., ozone or solar variability)
were not considered, the results suggest that the effects of enhanced greenhouse climate may be detected more readily in surface
temperatures from low-latitude oceanic regions than from global or zonal temperature averages.
Received: 27 June 1995/Accepted: 28 October 1996 相似文献
10.
Ocean iron fertilization has been proposed as a method to mitigate anthropogenic climate change, and there is continued commercial interest in using iron fertilization to generate carbon credits. It has been further speculated that ocean iron fertilization could help mitigate ocean acidification. Here, using a global ocean carbon cycle model, we performed idealized ocean iron fertilization simulations to place an upper bound on the effect of iron fertilization on atmospheric CO2 and ocean acidification. Under the IPCC A2 CO2 emission scenario, at year 2100 the model simulates an atmospheric CO2 concentration of 965 ppm with the mean surface ocean pH 0.44 units less than its pre-industrial value of 8.18. A globally sustained ocean iron fertilization could not diminish CO2 concentrations below 833 ppm or reduce the mean surface ocean pH change to less than 0.38 units. This maximum of 0.06 unit mitigation in surface pH change by the end of this century is achieved at the cost of storing more anthropogenic CO2 in the ocean interior, furthering acidifying the deep-ocean. If the amount of net carbon storage in the deep ocean by iron fertilization produces an equivalent amount of emission credits, ocean iron fertilization further acidifies the deep ocean without conferring any chemical benefit to the surface ocean. 相似文献
11.
Ten wheat production sites of Pakistan were categorized into four climatic zones i.e. arid, semi-arid, sub-humid and humid to explore the vulnerability of wheat production in these zones to climate change using CSM-Cropsim-CERES-Wheat model. The analysis was based on multi-year (1971–2000) crop model simulation runs using daily weather series under scenarios of increased temperature and atmospheric carbon dioxide concentration (CO2) along with two scenarios of water management. Apart from this, sowing date as an adaptation option to offset the likely impacts of climate change was also considered. Increase in temperature resulted in yield declines in arid, semi-arid and sub-humid zone. But the humid zone followed a positive trend of gain in yield with rise in temperature up to 4°C. Within a water regime, increase in CO2 concentration from 375 to 550 and 700 ppm will exert positive effect on gain in wheat yield but this positive effect is significantly variable in different climatic zones under rainfed conditions than the full irrigation. The highest response was shown by arid zone followed by semi-arid, sub-humid and humid zones. But if the current baseline water regimes (i.e. full irrigation in arid and semi-arid zones and rainfed in sub-humid and humid zones) persist in future, the sub-humid zone will be most benefited in terms of significantly higher percent gain in yield by increasing CO2 level, mainly because of its rainfed water regime. Within a CO2 level the changes in water supply from rainfed to full irrigation shows an intense degree of responsiveness in terms of yield gain at 375 ppm CO2 level compared to 550 and 700 ppm. Arid and semi-arid zones were more responsive compared to sub-humid and humid zones. Rise in temperature reduced the length of crop life cycle in all areas, though at an accelerated rate in the humid zone. These results revealed that the climatic zones have shown a variable intensity of vulnerability to different scenarios of climate change and water management due to their inherent specific and spatial climatic features. In order to cope with the negative effects of climate change, alteration in sowing date towards cooler months will be an appropriate response by the farmers. 相似文献
12.
Summary The transient response of the Southern Hemisphere to climate change is examined using an intermediate complexity climate model. Unlike previous studies, the Southern Ocean response on the centennial to multi-centennial time-scale is assessed in some detail. It is shown that changes in atmospheric CO2-concentrations lead to an increase in the strength of the Antarctic Circumpolar Current (ACC) by ∼20 Sv by 2750 for an atmospheric CO2-concentration of 750 ppm. This increase is predominantly the result of an enhanced steric height gradient. The increase in the strength of the ACC induces changes in its steering around topographic features. This change in ACC pathway causes increased surface flow of colder waters into some regions (reducing the rate of warming) and increased surface flow of warmer waters into others (increasing the rate of warming). This meridional shifting of the ACC causes changes in atmospheric temperature in the Southern Hemisphere to be nonuniform. It is also shown that the strength and location of the Antarctic Bottom Water (AABW) overturning cell is affected by increased atmospheric CO2. For a CO2-concentration scenario increasing gradually to 750 ppm, AABW production initially decreases, then recovers and eventually increases. New production zones form, which extend AABW production all the way from the Weddell Sea eastward into the Ross Sea. These new production zones are the result of increased areas of atmosphere-ocean interactions, due to decreased sea-ice coverage, although the overturned waters are now warmer and fresher due to climate change. A new production zone of Antarctic Intermediate water is also established in the Southeast Pacific Ocean, poleward of its present-day location. 相似文献
13.
In this study, a coupled atmosphere-surface “climate feedback-response analysis method” (CFRAM) was applied to the slab ocean model version of the NCAR CCSM3.0 to understand the tropospheric warming due to a doubling of CO2 concentration through quantifying the contributions of each climate feedback process. It is shown that the tropospheric warming displays distinct meridional and vertical patterns that are in a good agreement with the multi-model mean projection from the IPCC AR4. In the tropics, the warming in the upper troposphere is stronger than in the lower troposphere, leading to a decrease in temperature lapse rate, whereas in high latitudes the opposite it true. In terms of meridional contrast, the lower tropospheric warming in the tropics is weaker than that in high latitudes, resulting in a weakened meridional temperature gradient. In the upper troposphere the meridional temperature gradient is enhanced due to much stronger warming in the tropics than in high latitudes. Using the CFRAM method, we analyzed both radiative feedbacks, which have been emphasized in previous climate feedback analysis, and non-radiative feedbacks. It is shown that non-radiative (radiative) feedbacks are the major contributors to the temperature lapse rate decrease (increase) in the tropical (polar) region. Atmospheric convection is the leading contributor to temperature lapse rate decrease in the tropics. The cloud feedback also has non-negligible contributions. In the polar region, water vapor feedback is the main contributor to the temperature lapse rate increase, followed by albedo feedback and CO2 forcing. The decrease of meridional temperature gradient in the lower troposphere is mainly due to strong cooling from convection and cloud feedback in the tropics and the strong warming from albedo feedback in the polar region. The strengthening of meridional temperature gradient in the upper troposphere can be attributed to the warming associated with convection and cloud feedback in the tropics. Since convection is the leading contributor to the warming differences between tropical lower and upper troposphere, and between the tropical and polar regions, this study indicates that tropical convection plays a critical role in determining the climate sensitivity. In addition, the CFRAM analysis shows that convective process and water vapor feedback are the two major contributors to the tropical upper troposphere temperature change, indicating that the excessive upper tropospheric warming in the IPCC AR4 models may be due to overestimated warming from convective process or underestimated cooling due to water vapor feedback. 相似文献
14.
Vegetation is a major component of the climate system because of its controls on the energy and water balance over land. This functioning changes because of the physiological response of leaves to increased CO2. A climate model is used to compare these changes with the climate changes from radiative forcing by greenhouse gases. For this purpose, we use the Community Earth System Model coupled to a slab ocean. Ensemble integrations are done for current and doubled CO2. The consequent reduction of transpiration and net increase of surface radiative heating from reduction in cloudiness increases the temperature over land by a significant fraction of that directly from the radiative warming by CO2. Large-scale atmospheric circulation adjustments result. In particular, over the tropics, a low-level westerly wind anomaly develops associated with reduced geopotential height over land, enhancing moisture transport and convergence, and precipitation increases over the western Amazon, the Congo basin, South Africa, and Indonesia, while over mid-latitudes, land precipitation decreases from reduced evapotranspiration. On average, land precipitation is enhanced by 0.03 mm day?1 (about 19 % of the CO2 radiative forcing induced increase). This increase of land precipitation with decreased ET is an apparent negative feedback, i.e., less ET makes more precipitation. Global precipitation is slightly reduced. Runoff increases associated with both the increased land precipitation and reduced evapotranspiration. Examining the consistency of the variations among ensemble members shows that vegetation feedbacks on precipitation are more robust over the tropics and in mid to high latitudes than over the subtropics where vegetation is sparse and the internal climate variability has a larger influence. 相似文献
15.
Victor Brovkin Samuel Levis Marie-France Loutre Michel Crucifix Martin Claussen Andrey Ganopolski Claudia Kubatzki Vladimir Petoukhov 《Climatic change》2003,57(1-2):119-138
The stability of the climate-vegetation system in the northern high latitudesis analysed with three climate system models of different complexity: A comprehensive 3-dimensional model of the climate system, GENESIS-IBIS, and two Earth system models of intermediate complexity (EMICs), CLIMBER-2 andMoBidiC. The biogeophysical feedback in the latitudinal belt 60–70° N, although positive, is not strong enough to support multiple steady states: A unique equilibriumin the climate-vegetation system is simulated by all the models on a zonal scale for present-day climate and doubled CO2 climate.EMIC simulations with decreased insolation also reveal a unique steady state. However, the climate sensitivity to tree cover, TF, exhibits non-linear behaviour within the models. For GENESIS-IBIS and CLIMBER-2, TF islower for doubled CO2 climate than for present-day climate due to a shorter snow season and increased relative significance ofthe hydrological effect of forest cover. For the EMICs, TF is higher for low tree fraction than for high treefraction, mainly due to a time shift in spring snow melt in response to changes in tree cover. The climate sensitivity to tree coveris reduced when thermohaline circulation feedbacks are accounted for in the EMIC simulations. Simpler parameterizations of oceanic processes have opposite effects on TF: TF is lower in simulations with fixed SSTs and higher in simulations with mixed layer oceans. Experiments with transient CO2 forcing show climate and vegetation not in equilibrium in the northern high latitudes at the end of the 20thcentury. The delayed response of vegetation and accelerated global warming lead to rather abrupt changes in northern vegetation cover in the first halfof the 21st century, when vegetation cover changes at double the present day rate. 相似文献
16.
Future vegetation changes in thawing subarctic mires and implications for greenhouse gas exchange—a regional assessment 总被引：1，自引：1，他引：0
Julia Bosi? Margareta Johansson Terry V. Callaghan Bernt Johansen Torben R. Christensen 《Climatic change》2012,115(2):379-398
One of the major concerns regarding climate change in high latitudes is the potential feedback from greenhouse gases (GHG) being released from thawing peat soils. In this paper we show how vegetational patterns and associated GHG fluxes in subarctic palsa (peat mounds with a permanently frozen core) mires can be linked to climate, based on field observations from fifteen palsa sites distributed in northern Fennoscandia. Fine resolution (100?m) land cover data are combined with projections of future climate for the 21st century in order to model the potential future distribution of palsa vegetation in northern Fennoscandia. Site scale climate-vegetational relationships for two vegetation types are described by a climate suitability index computed from the field observations. Our results indicate drastic changes in the palsa vegetational patterns over the coming decades with a 97?% reduction in dry hummock areas by 2041?C2060 compared to the 1961?C1990 areal coverage. The impact of these changes on the carbon balance is a decrease in the efflux of CO2 from 130 kilotonnes C y?1 to a net uptake of 11 kilotonnes C y?1 and a threefold increase in the efflux of CH4 from 6 to 18 kilotonnes C y?1 over the same period and over the 5,520?km2 area of palsa mires. The combined effect is equivalent to a slight decrease in CO2-C emissions, from 182 to 152 kilotonnes C y?1. Main uncertainties involve the ability of the vegetation community to adapt to new conditions, and long-term changes in hydrology due to absence of ice and frost heaving. 相似文献
17.
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
18.
A coupled general circulation model has been used to perform a set of experiments with high CO2 concentration (2, 4, 16 times the present day mean value). The experiments have been analyzed to study the response of the climate system to strong radiative forcing in terms of the processes involved in the adjustment at the ocean–atmosphere interface. The analysis of the experiments revealed a non-linear response of the mean state of the atmosphere and ocean to the increase in the carbon dioxide concentration. In the 16 × CO2 experiment the equilibrium at the ocean–atmosphere interface is characterized by an atmosphere with a shut off of the convective precipitation in the tropical Pacific sector, associated with air warmer than the ocean below. A cloud feedback mechanism is found to be involved in the increased stability of the troposphere. In this more stable condition the mean total precipitation is mainly due to large-scale moisture flux even in the tropics. In the equatorial Pacific Ocean the zonal temperature gradient of both surface and sub-surface waters is significantly smaller in the 16 × CO2 experiment than in the control experiment. The thermocline slope and the zonal wind stress decrease as well. When the CO2 concentration increases by about two and four times with respect to the control experiment there is an intensification of El Niño. On the other hand, in the experiment with 16 times the present-day value of CO2, the Tropical Pacific variability weakens, suggesting the possibility of the establishment of permanent warm conditions that look like the peak of El Niño. 相似文献
19.
Climatic changes associated with a global “2°C-stabilization” scenario simulated by the ECHAM5/MPI-OM coupled climate model 总被引：1，自引：0，他引：1
Wilhelm May 《Climate Dynamics》2008,31(2-3):283-313
In this study, concentrations of the well-mixed greenhouse gases as well as the anthropogenic sulphate aerosol load and stratospheric ozone concentrations are prescribed to the ECHAM5/MPI-OM coupled climate model so that the simulated global warming does not exceed 2°C relative to pre-industrial times. The climatic changes associated with this so-called “2°C-stabilization” scenario are assessed in further detail, considering a variety of meteorological and oceanic variables. The climatic changes associated with such a relatively weak climate forcing supplement the recently published fourth assessment report by the IPCC in that such a stabilization scenario can only be achieved by mitigation initiatives. Also, the impact of the anthropogenic sulphate aerosol load and stratospheric ozone concentrations on the simulated climatic changes is investigated. For this particular climate model, the 2°C-stabilization scenario is characterized by the following atmospheric concentrations of the well-mixed greenhouse gases: 418 ppm (CO2), 2,026 ppb (CH4), and 331 ppb (N2O), 786 ppt (CFC-11) and 486 ppt (CFC-12), respectively. These greenhouse gas concentrations correspond to those for 2020 according to the SRES A1B scenario. At the same time, the anthropogenic sulphate aerosol load and stratospheric ozone concentrations are changed to the level in 2100 (again, according to the SRES A1B scenario), with a global anthropogenic sulphur dioxide emission of 28 TgS/year leading to a global anthropogenic sulphate aerosol load of 0.23 TgS. The future changes in climate associated with the 2°C-stabilization scenario show many of the typical features of other climate change scenarios, including those associated with stronger climatic forcings. That are a pronounced warming, particularly at high latitudes accompanied by a marked reduction of the sea-ice cover, a substantial increase in precipitation in the tropics as well as at mid- and high latitudes in both hemispheres but a marked reduction in the subtropics, a significant strengthening of the meridional temperature gradient between the tropical upper troposphere and the lower stratosphere in the extratropics accompanied by a pronounced intensification of the westerly winds in the lower stratosphere, and a strengthening of the westerly winds in the Southern Hemisphere extratropics throughout the troposphere. The magnitudes of these changes, however, are somewhat weaker than for the scenarios associated with stronger global warming due to stronger climatic forcings, such as the SRES A1B scenario. Some of the climatic changes associated with the 2°C-stabilization are relatively strong with respect to the magnitude of the simulated global warming, i.e., the pronounced warming and sea-ice reduction in the Arctic region, the strengthening of the meridional temperature gradient at the northern high latitudes and the general increase in precipitation. Other climatic changes, i.e., the El Niño like warming pattern in the tropical Pacific Ocean and the corresponding changes in the distribution of precipitation in the tropics and in the Southern Oscillation, are not as markedly pronounced as for the scenarios with a stronger global warming. A higher anthropogenic sulphate aerosol load (for 2030 as compared to the level in 2100 according to the SRES A1B scenario) generally weakens the future changes in climate, particularly for precipitation. The most pronounced effects occur in the Northern Hemisphere and in the tropics, where also the main sources of anthropogenic sulphate aerosols are located. 相似文献
20.
本文利用1980—1988年30°S—30°N的风场资料,计算了逐日的平均动能,涡动动能及相互转换和波数域动能;并分析了南、北半球热带对流层中层动能的演变特征,季节调整规律,指出了热带与中高纬动能的差异。 相似文献