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1.
The modification of greenhouse gas warming by the direct effect of sulphate aerosols 总被引:1,自引:0,他引:1
The Canadian Centre for Climate Modelling and Analysis (CCCma) second generation climate model (GCMII) consists of an atmospheric
GCM coupled to mixed layer ocean. It is used to investigate the climate response to a doubling of the CO2 concentration together with the direct effect of scattering by sulphate aerosols. As expected, the aerosols offset some of
the greenhouse gas (GHG) warming; the global annual mean screen temperature change due to doubled CO2 is 3.4 °C in this model and this is reduced to 2.7 °C when an estimate of the direct effect of anthropogenic sulphate aerosols
is included. The pattern of climate response to the comparatively localized aerosol forcing is not itself localized, and it
bears a striking resemblance to the response pattern that arises from the globally distributed change in GHG forcing. This
“non-local” response to “localized” forcing indicates that the pattern of climate response is determined, to first order,
by the overall magnitude of the change in forcing rather than its detailed nature or structure. Feedback processes operating
in the system apparently determine this pattern by locally amplifying and suppressing the response to the magnitude of the
change in forcing. The influence of the location of the change in forcing is relatively small. These “non-local” and “local”
effects of aerosol forcing are characterized and displayed and some of their consequences discussed. Effects on the moisture
budget and on the energetics of the global climate are also examined.
Received: 10 June 1997 / Accepted: 8 January 1998 相似文献
2.
Climate is simulated for reference and mitigation emissions scenarios from Integrated Assessment Models using the Bern2.5CC
carbon cycle–climate model. Mitigation options encompass all major radiative forcing agents. Temperature change is attributed
to forcings using an impulse–response substitute of Bern2.5CC. The contribution of CO2 to global warming increases over the century in all scenarios. Non-CO2 mitigation measures add to the abatement of global warming. The share of mitigation carried by CO2, however, increases when radiative forcing targets are lowered, and increases after 2000 in all mitigation scenarios. Thus,
non-CO2 mitigation is limited and net CO2 emissions must eventually subside. Mitigation rapidly reduces the sulfate aerosol loading and associated cooling, partly
masking Greenhouse Gas mitigation over the coming decades. A profound effect of mitigation on CO2 concentration, radiative forcing, temperatures and the rate of climate change emerges in the second half of the century. 相似文献
3.
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
4.
We assess two parametrisations of sea-ice in a coupled atmosphere–mixed layer ocean–sea-ice model. One parametrisation represents
the thermodynamic properties of sea-ice formation alone (THERM), while the other also includes advection of the ice (DYN).
The inclusion of some sea-ice dynamics improves the model's simulation of the present day sea-ice cover when compared to observations.
Two climate change scenarios are used to investigate the effect of these different parametrisations on the model's climate
sensitivity. The scenarios are the equilibrium response to a doubling of atmospheric CO2 and the response to imposed glacial boundary conditions. DYN produces a smaller temperature response to a doubling of CO2 than THERM. The temperature response of THERM is more similar to DYN in the glacial case than in the 2×CO2 case which implies that the climate sensitivity of THERM and DYN varies with the nature of the forcing. The different responses
can largely be explained by the different distribution of Southern Hemisphere sea-ice cover in the control simulations, with
the inclusion of ice dynamics playing an important part in producing the differences. This emphasises the importance of realistically
simulating the reference climatic state when attempting to simulate a climate change to a prescribed forcing. The simulated
glacial sea-ice cover is consistent with the limited palaeodata in both THERM and DYN, but DYN simulates a more realistic
present day sea-ice cover. We conclude that the inclusion of simple ice dynamics in our model increases our confidence in
the simulation of the anomaly climate.
Received: 24 May 2000 / Accepted: 25 October 2000 相似文献
5.
A transient climate change simulation with greenhouse gas and aerosol forcing: projected climate to the twenty-first century 总被引:3,自引:0,他引:3
The potential climatic consequences of increasing atmospheric greenhouse gas (GHG) concentration and sulfate aerosol loading
are investigated for the years 1900 to 2100 based on five simulations with the CCCma coupled climate model. The five simulations
comprise a control experiment without change in GHG or aerosol amount, three independent simulations with increasing GHG and
aerosol forcing, and a simulation with increasing GHG forcing only. Climate warming accelerates from the present with global
mean temperatures simulated to increase by 1.7 °C to the year 2050 and by a further 2.7 °C by the year 2100. The warming is
non-uniform as to hemisphere, season, and underlying surface. Changes in interannual variability of temperature show considerable
structure and seasonal dependence. The effect of the comparatively localized negative radiative forcing associated with the
aerosol is to retard and reduce the warming by about 0.9 °C at 2050 and 1.2 °C at 2100. Its primary effect on temperature
is to counteract the global pattern of GHG-induced warming and only secondarily to affect local temperatures suggesting that
the first order transient climate response of the system is determined by feedback processes and only secondarily by the local
pattern of radiative forcing. The warming is accompanied by a more active hydrological cycle with increases in precipitation
and evaporation rates that are delayed by comparison with temperature increases. There is an “El Nino-like” shift in precipitation
and an overall increase in the interannual variability of precipitation. The effect of the aerosol forcing is again primarily
to delay and counteract the GHG-induced increase. Decreases in soil moisture are common but regionally dependent and interannual
variability changes show considerable structure. Snow cover and sea-ice retreat. A PNA-like anomaly in mean sea-level pressure
with an enhanced Aleutian low in northern winter is associated with the tropical shift in precipitation regime. The interannual
variability of mean sea-level pressure generally decreases with largest decreases in the tropical Indian ocean region. Changes
to the ocean thermal structure are associated with a spin-down of the Atlantic thermohaline circulation together with a decrease
in its variability. The effect of aerosol forcing, although modest, differs from that for most other quantities in that it
does not act primarily to counteract the GHG forcing effect. The barotropic stream function in the ocean exhibits modest change
in the north Pacific but accelerating changes in much of the Southern Ocean and particularly in the north Atlantic where the
gyre spins down in conjunction with the decrease in the thermohaline circulation. The results differ in non-trivial ways from
earlier equilibrium 2 × CO2 results with the CCCma model as a consequence of the coupling to a fully three-dimensional ocean model and the evolving nature
of the forcing.
Received: 24 September 1998 / Accepted: 8 October 1999 相似文献
6.
Impulse-response-function (IRF) models are designed for applications requiring a large number of climate change simulations,
such as multi-scenario climate impact studies or cost-benefit integrated-assessment studies. The models apply linear response
theory to reproduce the characteristics of the climate response to external forcing computed with sophisticated state-of-the-art
climate models like general circulation models of the physical ocean-atmosphere system and three-dimensional oceanic-plus-terrestrial
carbon cycle models. Although highly computer efficient, IRF models are nonetheless capable of reproducing the full set of
climate-change information generated by the complex models against which they are calibrated. While limited in principle to
the linear response regime (less than about 3 ∘C global-mean temperature change), the applicability of the IRF model presented has been extended into the nonlinear domain
through explicit treatment of the climate system's dominant nonlinearities: CO2 chemistry in ocean water, CO2 fertilization of land biota, and sublinear radiative forcing. The resultant nonlinear impulse-response model of the coupled
carbon cycle-climate system (NICCS) computes the temporal evolution of spatial patterns of climate change for four climate
variables of particular relevance for climate impact studies: near-surface temperature, cloud cover, precipitation, and sea
level. The space-time response characteristics of the model are derived from an EOF analysis of a transient 850-year greenhouse
warming simulation with the Hamburg atmosphere-ocean general circulation model ECHAM3-LSG and a similar response experiment
with the Hamburg carbon cycle model HAMOCC. The model is applied to two long-term CO2 emission scenarios, demonstrating that the use of all currently estimated fossil fuel resources would carry the Earth's climate
far beyond the range of climate change for which reliable quantitative predictions are possible today, and that even a freezing
of emissions to present-day levels would cause a major global warming in the long term.
Received: 28 January 2000 / Accepted: 9 March 2001 相似文献
7.
Jonghan Ko Lajpat R. Ahuja S. A. Saseendran Timothy R. Green Liwang Ma David C. Nielsen Charles L. Walthall 《Climatic change》2012,111(2):445-472
Agricultural systems models are essential tools to assess potential climate change (CC) impacts on crop production and help
guide policy decisions. In this study, impacts of projected CC on dryland crop rotations of wheat-fallow (WF), wheat-corn-fallow
(WCF), and wheat-corn-millet (WCM) in the U.S. Central Great Plains (Akron, Colorado) were simulated using the CERES V4.0
crop modules in RZWQM2. The CC scenarios for CO2, temperature and precipitation were based on a synthesis of Intergovernmental Panel on Climate Change (IPCC 2007) projections for Colorado. The CC for years 2025, 2050, 2075, and 2100 (CC projection years) were super-imposed on measured
baseline climate data for 15–17 years collected during the long-term WF and WCF (1992–2008), and WCM (1994–2008) experiments
at the location to provide inter-annual variability. For all the CC projection years, a decline in simulated wheat yield and
an increase in actual transpiration were observed, but compared to the baseline these changes were not significant (p > 0.05) in all cases but one. However, corn and proso millet yields in all rotations and projection years declined significantly
(p < 0.05), which resulted in decreased transpiration. Overall, the projected negative effects of rising temperatures on crop
production dominated over any positive impacts of atmospheric CO2 increases in these dryland cropping systems. Simulated adaptation via changes in planting dates did not mitigate the yield
losses of the crops significantly. However, the no-tillage maintained higher wheat yields than the conventional tillage in
the WF rotation to year 2075. Possible effects of historical CO2 increases during the past century (from 300 to 380 ppm) on crop yields were also simulated using 96 years of measured climate
data (1912–2008) at the location. On average the CO2 increase enhanced wheat yields by about 30%, and millet yields by about 17%, with no significant changes in corn yields. 相似文献
8.
S. Gonzi O. Dubovik D. Baumgartner E. Putz 《Meteorology and Atmospheric Physics》2007,96(3-4):277-291
Summary One of the great unknowns in climate research is the contribution of aerosols to climate forcing and climate perturbation.
In this study, retrievals from AERONET are used to estimate the direct clear-sky aerosol top-of-atmosphere and surface radiative
forcing effects for 12 multi-site observing stations in Europe. The radiative transfer code sdisort in the libRadtran environment is applied to accomplish these estimations. Most of the calculations in this study rely on observations which
have been made for the years 1999, 2000, and 2001. Some stations do have observations dating back to the year of 1995. The
calculations rely on a pre-compiled aerosol optical properties database for Europe. Aerosol radiative forcing effects are
calculated with monthly mean aerosol optical properties retrievals and calculations are presented for three different surface
albedo scenarios. Two of the surface albedo scenarios are generic by nature bare soil and green vegetation and the third relies on the ISCCP (International Satellite Cloud Climatology Project) data product. The ISCCP database has
also been used to obtain clear-sky weighting fractions over AERONET stations. The AERONET stations cover the area 0° to 30° E
and 42° to 52° N. AERONET retrievals are column integrated and this study does not make any seperation between the contribution
of natural and anthropogenic components. For the 12 AERONET stations, median clear-sky top-of-atmosphere aerosol radiative
forcing effect values for different surface albedo scenarios are calculated to be in the range of −4 to −2 W/m2. High median radiative forcing effect values of about −6 W/m2 were found to occur mainly in the summer months while lower values of about −1 W/m2 occur in the winter months. The aerosol surface forcing also increases in summer months and can reach values of −8 W/m2. Individual stations often have much higher values by a factor of 2. The median top-of-atmosphere aerosol radiative forcing
effect efficiency is estimated to be about −25 W/m2 and their respective surface efficiency is around −35 W/m2. The fractional absorption coefficient is estimated to be 1.7, but deviates significantly from station to station. In addition,
it is found that the well known peak of the aerosol radiative forcing effect at a solar zenith angle of about 75° is in fact
the average of the peaks occurring at shorter and longer wavelengths. According to estimations for Central Europe, based on
mean aerosol optical properties retrievals from 12 stations, the critical threshold of the aerosol single scattering albedo,
between cooling and heating in the presence of an aerosol layer, is close between 0.6 and 0.76. 相似文献
9.
The radiative flux perturbations and subsequent temperature responses in relation to the eruption of Mount Pinatubo in 1991
are studied in the ten general circulation models incorporated in the Coupled Model Intercomparison Project, phase 3 (CMIP3),
that include a parameterization of volcanic aerosol. Models and observations show decreases in global mean temperature of
up to 0.5 K, in response to radiative perturbations of up to 10 W m−2, averaged over the tropics. The time scale representing the delay between radiative perturbation and temperature response
is determined by the slow ocean response, and is estimated to be centered around 4 months in the models. Although the magniude
of the temperature response to a volcanic eruption has previously been used as an indicator of equilibrium climate sensitivity
in models, we find these two quantities to be only weakly correlated. This may partly be due to the fact that the size of
the volcano-induced radiative perturbation varies among the models. It is found that the magnitude of the modelled radiative
perturbation increases with decreasing climate sensitivity, with the exception of one outlying model. Therefore, we scale
the temperature perturbation by the radiative perturbation in each model, and use the ratio between the integrated temperature
perturbation and the integrated radiative perturbation as a measure of sensitivity to volcanic forcing. This ratio is found
to be well correlated with the model climate sensitivity, more sensitive models having a larger ratio. Further, if this correspondence
between “volcanic sensitivity” and sensitivity to CO2 forcing is a feature not only among the models, but also of the real climate system, the alleged linear relation can be used
to estimate the real climate sensitivity. The observational value of the ratio signifying volcanic sensitivity is hereby estimated
to correspond to an equilibrium climate sensitivity, i.e. equilibrium temperature increase due to a doubling of the CO2 concentration, between 1.7 and 4.1 K. Several sources of uncertainty reside in the method applied, and it is pointed out
that additional model output, related to ocean heat storage and radiative forcing, could refine the analysis, as could reduced
uncertainty in the observational record, of temperature as well as forcing. 相似文献
10.
Jeffery R. Scott Andrei P. Sokolov Peter H. Stone Mort D. Webster 《Climate Dynamics》2008,30(5):441-454
The response of the ocean’s meridional overturning circulation (MOC) to increased greenhouse gas forcing is examined using
a coupled model of intermediate complexity, including a dynamic 3-D ocean subcomponent. Parameters are the increase in CO2 forcing (with stabilization after a specified time interval) and the model’s climate sensitivity. In this model, the cessation
of deep sinking in the north “Atlantic” (hereinafter, a “collapse”), as indicated by changes in the MOC, behaves like a simple
bifurcation. The final surface air temperature (SAT) change, which is closely predicted by the product of the radiative forcing
and the climate sensitivity, determines whether a collapse occurs. The initial transient response in SAT is largely a function
of the forcing increase, with higher sensitivity runs exhibiting delayed behavior; accordingly, high CO2-low sensitivity scenarios can be assessed as a recovering or collapsing circulation shortly after stabilization, whereas
low CO2-high sensitivity scenarios require several hundred additional years to make such a determination. We also systemically examine
how the rate of forcing, for a given CO2 stabilization, affects the ocean response. In contrast with previous studies based on results using simpler ocean models,
we find that except for a narrow range of marginally stable to marginally unstable scenarios, the forcing rate has little
impact on whether the run collapses or recovers. In this narrow range, however, forcing increases on a time scale of slow
ocean advective processes results in weaker declines in overturning strength and can permit a run to recover that would otherwise
collapse. 相似文献
11.
Benjamin D. Santer Karl E. Taylor Tom M. L. Wigley Joyce E. Penner Philip D. Jones Ulrich Cubasch 《Climate Dynamics》1995,12(2):77-100
It has been hypothesized recently that regional-scale cooling caused by anthropogenic sulfate aerosols may be partially obscuring
a warming signal associated with changes in greenhouse gas concentrations. Here we use results from model experiments in which
sulfate and carbon dioxide have been varied individually and in combination in order to test this hypothesis. We use centered
[R (t)] and uncentered [C (t)] pattern similarity statistics to compare observed time-evolving surface temperature change patterns with the model-predicted
equilibrium signal patterns. We show that in most cases, the C (t) statistic reduces to a measure of observed global-mean temperature changes, and is of limited use in attributing observed
climate changes to a specific causal mechanism. We therefore focus on R (t), which is a more useful statistic for discriminating between forcing mechanisms with different pattern signatures but similar
rates of global mean change. Our results indicate that over the last 50 years, the summer (JJA) and fall (SON) observed patterns
of near-surface temperature change show increasing similarity to the model-simulated response to combined sulfate aerosol/CO2 forcing. At least some of this increasing spatial congruence occurs in areas where the real world has cooled. To assess the
significance of the most recent trends in R (t) and C (t), we use data from multi-century control integrations performed with two different coupled atmosphere-ocean models, which
provide information on the statistical behavior of 'unforced' trends in the pattern correlation statistics. For the combined
sulfate aerosol/CO2 experiment, the 50-year R (t) trends for the JJA and SON signals are highly significant. Results are robust in that they do not depend on the choice of
control run used to estimate natural variability noise properties. The R (t) trends for the CO2-only signal are not significant in any season. C (t) trends for signals from both the CO2-only and combined forcing experiments are highly significant in all seasons and for all trend lengths (except for trends
over the last 10 years), indicating large global-mean changes relative to the two natural variability estimates used here.
The caveats regarding the signals and natural variability noise which form the basis of this study are numerous. Nevertheless,
we have provided first evidence that both the largest-scale (global-mean) and smaller-scale (spatial anomalies about the global
mean) components of a combined CO2/anthropogenic sulfate aerosol signal are identifiable in the observed near-surface air temperature data. If the coupled-model
noise estimates used here are realistic, we can be highly confident that the anthropogenic signal that we have identified
is distinctly different from internally generated natural variability noise. The fact that we have been able to detect the
detailed spatial signature in response to combined CO2 and sulfate aerosol forcing, but not in response to CO2 forcing alone, suggests that some of the regional-scale background noise (against which we were trying to detect a CO2-only signal) is in fact part of the signal of a sulfate aerosol effect on climate. The large effect of sulfate aerosols found
in this study demonstrates the importance of their inclusion in experiments designed to simulate past and future climate change.
Received: 10 November 1994 / Accepted: 19 July 1995 相似文献
12.
L. D. Danny Harvey 《Climatic change》2007,82(1-2):1-25
Article 2 of the United Nations Framework Convention on Climate Change (UNFCCC) calls for stabilization of greenhouse gas
(GHG) concentrations at levels that prevent dangerous anthropogenic interference (DAI) in the climate system. However, some
of the recent policy literature has focused on dangerous climatic change (DCC) rather than on DAI. DAI is a set of increases
in GHGs concentrations that has a non-negligible possibility of provoking changes in climate that in turn have a non-negligible
possibility of causing unacceptable harm, including harm to one or more of ecosystems, food production systems, and sustainable
socio-economic systems, whereas DCC is a change of climate that has actually occurred or is assumed to occur and that has
a non-negligible possibility of causing unacceptable harm. If the goal of climate policy is to prevent DAI, then the determination
of allowable GHG concentrations requires three inputs: the probability distribution function (pdf) for climate sensitivity,
the pdf for the temperature change at which significant harm occurs, and the allowed probability (“risk”) of incurring harm
previously deemed to be unacceptable. If the goal of climate policy is to prevent DCC, then one must know what the correct
climate sensitivity is (along with the harm pdf and risk tolerance) in order to determine allowable GHG concentrations. DAI
from elevated atmospheric CO2 also arises through its impact on ocean chemistry as the ocean absorbs CO2. The primary chemical impact is a reduction in the degree of supersaturation of ocean water with respect to calcium carbonate,
the structural building material for coral and for calcareous phytoplankton at the base of the marine food chain. Here, the
probability of significant harm (in particular, impacts violating the subsidiary conditions in Article 2 of the UNFCCC) is
computed as a function of the ratio of total GHG radiative forcing to the radiative forcing for a CO2 doubling, using two alternative pdfs for climate sensitivity and three alternative pdfs for the harm temperature threshold.
The allowable radiative forcing ratio depends on the probability of significant harm that is tolerated, and can be translated
into allowable CO2 concentrations given some assumption concerning the future change in total non-CO2 GHG radiative forcing. If future non-CO2 GHG forcing is reduced to half of the present non-CO2 GHG forcing, then the allowable CO2 concentration is 290–430 ppmv for a 10% risk tolerance (depending on the chosen pdfs) and 300–500 ppmv for a 25% risk tolerance
(assuming a pre-industrial CO2 concentration of 280 ppmv). For future non-CO2 GHG forcing frozen at the present value, and for a 10% risk threshold, the allowable CO2 concentration is 257–384 ppmv. The implications of these results are that (1) emissions of GHGs need to be reduced as quickly
as possible, not in order to comply with the UNFCCC, but in order to minimize the extent and duration of non-compliance; (2)
we do not have the luxury of trading off reductions in emissions of non-CO2 GHGs against smaller reductions in CO2 emissions, and (3) preparations should begin soon for the creation of negative CO2 emissions through the sequestration of biomass carbon. 相似文献
13.
J. Räisänen 《Climate Dynamics》1997,13(3):197-211
Four transient GCM experiments simulating the climatic response to gradually increasing CO2, and two equilibrium doubled CO2 experiments are compared. The zonally symmetric and asymmetric features of climate are both examined. Surface air temperature,
sea level pressure, the 500 mb height and the relative topography between 500 and 1000 mb are analyzed. In the control simulations,
the broad aspects of the present climate are in most cases well reproduced, although the stationary eddies tend to be less
reliably simulated than the zonal means. However, the agreement between the four transient experiments on the geographical
patterns of climate change is less impressive. While some zonally symmetric features, in particular the meridional distribution
of surface air warming in the boreal winter, are rather similar in all models, the intermodel cross correlations for the zonally
asymmetric changes are low. The agreement is largely restricted to some very general features such as more warming over the
continents than over the oceans. The largest discrepancies between the two equilibrium-doubled CO2 experiments and the transient experiments are found at the high southern latitudes, in particular in the austral winter.
To identify the most robust geographical patterns of change in the transient experiments, the standard t test is used to determine if the four-model mean change is significantly above or below the global mean.
Received: 18 January 1996 / Accepted: 5 July 1996 相似文献
14.
With the continuing warming due to greenhouse gases concentration, it is important to examine the potential impacts on regional
crop production spatially and temporally. We assessed China’s potential maize production at 50 × 50 km grid scale under climate
change scenarios using modelling approach. Two climate changes scenarios (A2 and B2) and three time slices (2011–2040, 2041–2070,
2071–2100) produced by the PRECIS Regional Climate Model were used. Rain-fed and irrigated maize yields were simulated with
the CERES-Maize model, with present optimum management practices. The model was run for 30 years of baseline climate and three
time slices for the two climate change scenarios, without and with simulation of direct CO2 fertilization effects. Crop simulation results under climate change scenarios varied considerably between regions and years.
Without the CO2 fertilization effect, China’s maize production was predicted to suffer a negative effect under both A2 and B2 scenarios for
all time slices, with greatest production decreases in today’s major maize planting areas. When the CO2 fertilization effect is taken into account, production was predicted to increase for rain-fed maize but decrease for irrigated
maize, under both A2 and B2 scenarios for most time periods. 相似文献
15.
A general circulation model is used to examine the effects of reduced atmospheric CO2, insolation changes and an updated reconstruction of the continental ice sheets at the Last Glacial Maximum (LGM). A set
of experiments is performed to estimate the radiative forcing from each of the boundary conditions. These calculations are
used to estimate a total radiative forcing for the climate of the LGM. The response of the general circulation model to the
forcing from each of the changed boundary conditions is then investigated. About two-thirds of the simulated glacial cooling
is due to the presence of the continental ice sheets. The effect of the cloud feedback is substantially modified where there
are large changes to surface albedo. Finally, the climate sensitivity is estimated based on the global mean LGM radiative
forcing and temperature response, and is compared to the climate sensitivity calculated from equilibrium experiments with
atmospheric CO2 doubled from present day concentration. The calculations here using the model and palaeodata support a climate sensitivity
of about 1 Wm-2 K-1 which is within the conventional range.
Received: 8 February 1997 / Accepted: 4 June 1997 相似文献
16.
We compared regional biases and transient doubled CO2 sensitivities of nine coupled atmosphere-ocean general circulation models (GCMs) from six international climate modeling
groups. We evaluated biases and responses in winter and summer surface air temperatures and precipitation for seven subcontinental
regions, including those in the 1990 Intergovernmental Panel on Climate Change (IPCC) Scientific Assessment. Regional biases
were large and exceeded the variance among four climatological datasets, indicating that model biases were not primarily due
to uncertainty in observations. Model responses to altered greenhouse forcing were substantial (average temperature change=2.7±0.9 °C, range of precipitation change =−35 to +120% of control). While coupled models include more climate system feedbacks than
earlier GCMs implemented with mixed-layer ocean models, inclusion of a dynamic ocean alone did not improve simulation of long-term
mean climatology nor increase convergence among model responses to altered greenhouse gas forcing. On the other hand, features
of some of the coupled models including flux adjustment (which may have simply masked simulation errors), high horizontal
resolution, and estimation of screen height temperature contributed to improved simulation of long-term surface climate. The
large range of model responses was partly accounted for by inconsistencies in forcing scenarios and transient-simulation averaging
periods. Nonetheless, the models generally had greater agreement in their sensitivities than their controls did with observations.
This suggests that consistent, large-scale response features from an ensemble of model sensitivity experiments may not depend
on details of their representation of present-day climate.
Received: 9 September 1996 / Revised: 31 July 1997 相似文献
17.
Modelling climate change impacts on maize growth and development in the Czech Republic 总被引:5,自引:0,他引:5
Summary The crop growth model CERES-Maize is used to estimate the direct (through enhanced fertilisation effect of ambient CO2) and indirect (through changed climate conditions) effects of increased concentration of atmospheric CO2 on maize yields. The analysis is based on multi-year crop model simulations run with daily weather series obtained alternatively
by a direct modification of observed weather series and by a stochastic weather generator. The crop model is run in two settings:
stressed yields are simulated in water and nutrient limited conditions, potential yields in water and nutrient unlimited conditions.
The climate change scenario was constructed using the output from the ECHAM3/T42 model (temperature), regression relationships
between temperature and solar radiation, and an expert judgement (precipitation).
Results: (i) After omitting the two most extreme misfits, the standard error between the observed and modelled yields is 11%.
(ii) The direct effect of doubled CO2: The stressed yields would increase by 36–41% in the present climate and by 61–66% in the 2 × CO2 climate. The potential yields would increase only by 9–10% as the improved water use efficiency does not apply. (iii) The
indirect effect of doubled CO2: The stressed yields would decrease by 27–29% (14–16%) at present (doubled) ambient CO2 concentration. The increased temperature shortens the phenological phases and does not allow for the optimal development
of the crop. The simultaneous decrease of precipitation and increase of temperature and solar radiation deepen the water stress,
thereby reducing the yields. The reduction of the potential yields is significantly smaller as the effect of the increased
water stress does not apply. (iv) If both direct and indirect effects of doubled CO2 are considered, the stressed yields should increase by 17–18%, and the potential yields by 5–14%. (v) The decrease of the
stressed yields due to the indirect effect may be reduced by applying earlier planting dates.
Received March 9, 2001 Revised September 25, 2001 相似文献
18.
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
19.
Observed and projected climate change in Taiwan 总被引:1,自引:0,他引:1
Summary
This study examined the secular climate change characteristics in Taiwan over the past 100 years and the relationship with
the global climate change. Estimates for the likelihood of future climate changes in Taiwan were made based on the projection
from the IPCC climate models.
In the past 100 years, Taiwan experienced an island-wide warming trend (1.0–1.4 °C/100 years). Both the annual and daily temperature
ranges have also increased. The warming in Taiwan is closely connected to a large-scale circulation and SAT fluctuations,
such as the “cool ocean warm land” phenomenon. The water vapor pressure has increased significantly and could have resulted
in a larger temperature increase in summer. The probability for the occurrence of high temperatures has increased and the
result suggests that both the mean and variance in the SAT in Taiwan have changed significantly since the beginning of the
20th century. Although, as a whole, the precipitation in Taiwan has shown a tendency to increase in northern Taiwan and to
decrease in southern Taiwan in the past 100 years, it exhibits a more complicated spatial pattern. The changes occur mainly
in either the dry or rainy season and result in an enhanced seasonal cycle. The changes in temperature and precipitation are
consistent with the weakening of the East Asian monsoon.
Under consideration of both the warming effect from greenhouse gases and the cooling effect from aerosols, all projections
from climate models indicated a warmer climate near Taiwan in the future. The projected increase in the area-mean temperature
near Taiwan ranged from 0.9–2.7 °C relative to the 1961–1990 averaged temperature, when the CO2 concentration increased to 1.9 times the 1961–1990 level. These simulated temperature increases were statistically significant
and can be attributed to the radiative forcing associated with the increased concentration of greenhouse gases and aerosols.
The projected changes in precipitation were within the range of natural variability for all five models. There is no evidence
supporting the possibility of precipitation changes near Taiwan based on the simulations from five IPCC climate models.
Received February 5, 2001 Revised July 30, 2001 相似文献
20.
K. D. Williams A. Jones D. L. Roberts C. A. Senior M. J. Woodage 《Climate Dynamics》2001,17(11):845-856
The indirect effects of anthropogenic sulfate aerosols on the albedo and lifetime of clouds may produce a significant impact
on the climate system. A `state of the art' general circulation model (GCM) which includes an interactive sulfur cycle and
a physically based cloud microphysics scheme is coupled to a mixed-layer ocean model in order to study the impact of the indirect
effects on the coupled climate system. The linearity of the two indirect effects on the model response is also investigated
by including each effect separately in the model. The response of the sea surface temperatures (SSTs) and sea ice is found
to provide an important feedback on the cooling at high latitudes and the change in meridional SST gradient results in a southward
shift of the inter-tropical convergence zone (ITCZ). The sensitivity of the model to the forcing from the indirect effects
of sulfate aerosol is found to be similar to, but slightly weaker than that obtained from a doubling of CO2.
Received: 30 August 2000 / Accepted: 3 January 2001 相似文献