The buffer capability of the ocean to increasing atmospheric CO2

The CO2-seawaler system and the method for calculating the partial pressure of CO2 (pCO3) in seawater are stu-died. The buffer capability of the ocean to increasing atmospheric CO2, is expressed in terms of the differential buffer factor and buffer index. Dissolutions of aragonite and calcite have a significant influence on the differential buffer factor. The trend of change in the buffer factor is obtained by a box model.     

Hydrological changes in the climate system from leaf responses to increasing CO2

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.     

Effect of increasing CO2 on the stratospheric level of CO and O3

Production and destruction processes of carbon monoxide (CO) and ozone (O3) are examined in the light of increasing amount of atmospheric carbon dioxide (CO2). It is found that doubling of CO2 will increase the stratospheric concentration of CO and will have positive effect on O3 concentration.     

Impact of increasing CO2 on monthly-to-annual precipitation extremes: analysis of the CMIP2 experiments

The impact of increasing atmospheric CO₂ on high and low extremes of monthly-to-annual precipitation is studied using 20 model experiments participating in the second phase of the coupled model intercomparison project (CMIP2). In marked contrast with previous research on daily precipitation extremes, the simulated changes in extremes on these longer time scales are well correlated with the changes in the long-term mean precipitation: wet extremes become more severe especially where the mean precipitation increases, and dry extremes where the mean precipitation decreases. Changes in relative variability play a smaller but discernible role. In an ensemble-mean sense, the variability increases slightly in most areas, so that the contrast between the high and low precipitation extremes grows larger with increasing CO₂. The changes in the frequency of extremes (fraction of cases with precipitation above a high or below a low predefined threshold) are much larger than the changes in their magnitude. Most of the ensemble-averaged changes in the frequency of extremes can be reconstructed by using the changes in time mean precipitation alone, provided that the variation in time mean precipitation change between different models is taken into account. The nonlinear relationship between the mean precipitation and the frequency of extremes complicates the interpretation of the frequency changes, especially when averaging frequencies over different models.     

An assessment of measures of storminess: simulated changes in northern hemisphere winter due to increasing CO2

Two methods for identifying mid-latitude synoptic time scale variability have been applied to data from the first United Kingdom Meteorological Office (UKMO) coupled ocean-atmosphere model experiments with present day and gradually increasing CO₂ concentrations. In the first the standard deviation of the time filtered mean sea level pressure field is taken to identify the location of the storm track and in the second individual cyclones are identified using synoptic criteria. The results have been compared with data from a 10 year archive of UKMO analysis. In the enhanced CO₂ experiment the changes in storminess identified by the two methods have been compared with changes in mean and maximum winds with special emphasis on the North Atlantic. The relative utility of the different measures for predicting potentially damaging synoptic events is discussed. Received: 3 May 1995 / Accepted: 7 November 1995     

An assessment of measures of storminess: Simulated changes in northern hemisphere winter due to increasing CO2

Two methods for identifying mid-latitude synoptic time scale variability have been applied to data from the first United Kingdom Meteorological Office (UKMO) coupled ocean-atmosphere model experiments with present day and gradually increasing CO₂ concentrations. In the first the standard deviation of the time filtered mean sea level pressure field is taken to identify the location of the storm track and in the second individual cyclones are identified using synoptic criteria. The results have been compared with data from a 10 year archive of UKMO analysis. In the enhanced CO₂ experiment the changes in storminess identified by the two methods have been compared with changes in mean and maximum winds with special emphasis on the North Atlantic. The relative utility of the different measures for predicting potentially damaging synoptic events is discussed.     

Climate change in the Paraná state,Brazil: responses to increasing atmospheric CO 2 in reference evapotranspiration

The hydrological variable evapotranspiration (ET) is challenging to estimate because it cannot be measured directly in natural environments (except in small plots). The uncertainties associated with the models used for its prediction have increased under climate change conditions. We studied the influence of stomatal resistance on ET estimates using the Penman-Monteith method as projected by three general circulation models in two emission scenarios (RCP4.5 and RCP8.5) for future climates throughout the twenty-first century (2010–2039, 2040–2069, and 2070–2099). We also investigated the probable ET rate changes in relation to the current (30 years average, 1980–2009) climate conditions for the Paraná state in the southern region of Brazil. The results were regionalized to help policymakers assess climate change impacts and design adaptation measures. ET increases of up to 15% were found in future climate conditions, which may lead to a significant increase in the water demand for agricultural crops. However, we believe that plant morphophysiological changes may occur under atmospheric CO2 enrichment conditions and that a possible reduction in stomatal conductance will result in lower ET increases than those obtained with the traditional Penman-Monteith method. When considering future climate scenarios, we propose the equation be adjusted to consider stomatal resistance as a function of CO2 concentrations.     

Fast and slow timescales in the tropical low-cloud response to increasing CO2 in two climate models

To obtain physical insights into the response and feedback of low clouds (C _l ) to global warming, ensemble 4?×?CO₂ experiments were carried out with two climate models, the Model for Interdisciplinary Research on Climate (MIROC) versions 3.2 and 5. For quadrupling CO₂, tropical-mean C _l decreases, and hence, acts as positive feedback in MIROC3, whereas it increases and serves as negative feedback in MIROC5. Three time scales of tropical-mean C _l change were identified—an initial adjustment without change in the global-mean surface air temperature, a slow response emerging after 10–20?years, and a fast response in between. The two models share common features for the former two changes in which C _l decreases. The slow response reflects the variability of C _l associated with the El Ni?o-Southern Oscillation in the control integration, and may therefore be constrained by observations. However, the fast response is opposite in the two models and dominates the total response of C _l . Its sign is determined by a subtle residual of the C _l increase and decrease over the ascending and subsidence regions, respectively. The regional C _l increase is consistent with a more frequent occurrence of a stable condition, and vice versa, as measured by lower-tropospheric stability (LTS). The above frequency change in LTS is similarly found in six other climate models despite a large difference in both the mean and the changes in the low-cloud fraction for a given LTS. This suggests that the response of the thermodynamic constraint for C _l to increasing CO₂ concentrations is a robust part of the climate change.     

Feedbacks affecting the response of the thermohaline circulation to increasing CO2: a study with a model of intermediate complexity

A three-dimensional ocean model with an idealized geometry and coarse resolution coupled to a two-dimensional (zonally averaged) statistical-dynamical atmospheric model is used to simulate the response of the thermohaline circulation to increasing CO ₂ concentration in the atmosphere. The relative roles of different factors in the slowing down and recovery of the thermohaline circulation were studied by performing simulations with ocean only and partially coupled models. The computational efficiency of the model allows an extensive and thorough study of the causes of changes in the strength of the thermohaline circulation, through a large number of extended runs. The evolution of the atmosphere-to-ocean surface heat fluxes is shown to be the dominant factor in causing the weakening of the circulation in response to an increasing external forcing as well as in controlling the subsequent recovery. The feedback between heat flux and the sea surface temperature is necessary for the ocean circulation to recover. The rate of the recovery, however, is not sensitive to the magnitude of the feedback, and changes in the atmosphere, while contributing to the recovery, play a secondary role. In the case of very strong feedback, substantial changes in the SST structure are shown not to be a necessary condition for the recovery of the circulation. Subsurface changes in the density structure accompany recovery despite nearly fixed SST in one of the uncoupled experiments. Changes in the zonal distribution of heat fluxes serve as a positive feedback for both decrease and recovery of the meridional overturning, and are as important as changes in the zonal-mean values of heat fluxes. The secondary role of the moisture fluxes is explained by a smaller magnitude of their contribution to the surface buoyancy flux. Imposing amplified changes in the moisture fluxes leads to a significant slow down of the circulation, accompanied, however, by changes in the heat flux. The changed heat flux, in its turn, makes a significant contribution to the future slow down. This feedback complicates the evaluation of the relative roles of the different fluxes.     

Changes in Heat Index Associated with CO2-Induced Global Warming

Changes in Heat Index (a combined measure of temperature and humidity) associated with global warming are evaluated based on the output from four extended integrations of the GFDL coupled ocean-atmosphere climate model. The four integrations are: a control with constant levels of atmospheric carbon dioxide (CO₂), a second integration in which an estimate of the combined radiative forcing of greenhouse gases and sulfate aerosols over the period 1765–2065 is used to force the model, and a third (fourth) integration in which atmospheric CO₂$ increases at the rate of 1% per year to double (quadruple) its initial value, and is held constant thereafter. While the spatial patterns of the changes in Heat Index are largely determined by the changes in surface air temperature, increases in atmospheric moisture can substantially amplify the changes in Heat Index over regions which are warm and humid in the Control integration. The regions most prone to this effect include humid regions of the Tropics and summer hemisphere extra-tropics, including the southeastern United States, India, southeast Asia and northern Australia.     

CO2浓度增加背景下季风区大气辐射加热响应的差异

大气CO2浓度增加,大气辐射平衡调整,将影响到大气的辐射加热,对季风环流的产生影响.CMIP6结果显示,大气CO2浓度增加,可减弱季风区主雨季对流层高,低层的辐射加热,加强对流层中层的辐射加热.各季风区加热响应的峰值层次不同:亚洲季风区平均层次最高(500-775 hPa),北非,南美,澳洲季风区次之(550-600 ...     

Influence of natural variability and the cold start problem on the simulated transient response to increasing CO2

 The Hadley Centre coupled ocean-atmosphere general circulation model (AOGCM) has been used to study the effect of including the historical increase in greenhouse gases from 1860 to 1990 on the response to a subsequent 1% per year increase in CO₂. Results from an ensemble of four experiments which include the historical increase, warm start (WS) experiments, are compared with an ensemble of four experiments which do not include the historical increase, cold start (CS) experiments. In the WS experiments, oceanic thermal inertia prevents the model from reaching equilibrium with the historical change in forcing from 1860 to 1990. This implies an unrealised warming at 1990, defined here as the ‘warming commitment’, increasing the subsequent warming in WS relative to that in CS. The difference in response between a WS experiment and a CS experiment is defined as the cold start error. For surface temperature the ensemble-mean cold start error is 20% of the WS response after year 30 and 10% at the time of doubling CO₂ (year 70). For sea level the reduction in the CS response is more pronounced, amounting to 60% at year 30 and 40% at the time of doubling. The vertical transfer of heat in the ocean is found to correspond to an equivalent diffusion process. This result supports the use of simple ocean models with constant diffusivity to produce time-dependent scenarios of globally averaged climate change, subject to the caveat that the changes in ocean circulation simulated by the present AOGCM were smaller than in some previous cases. In the WS integrations the vertical temperature gradient is larger than in CS due to the historical forcing influence, leading to more efficient heat loss from the base of the mixed layer and hence a larger effective heat capacity. This explains why the cold start error for surface temperature is smaller than for sea level. By year 50 the global patterns of temperature change in individual integrations are highly correlated in both the WS and CS ensembles, indicating that natural variability is too small to conceal the climate change signal. The simulated regional changes are statistically significant almost everywhere after 30 y. Before year 30, when the signal-to-noise ratio is smaller, ensemble averaging the changes leads to a substantial increase in significance. In contrast to a previous study also based on an ensemble of integrations, significant changes in precipitation and soil moisture are found. For these quantities the area of significant change grows more slowly with time, however ensemble averaging increases the significant area throughout. The characteristic patterns of change in WS and CS are similar, and evident in the simulation of the past record. This suggests that the component of the historical patterns of change, driven by greenhouse gas forcing, is likely to bear significant similarities to the patterns expected in the future. However, significant regional differences do develop between the WS and CS ensembles. The cold start error has a non-uniform pattern which becomes established in the second half of the experiment, and is not a simple amplification or modulation of the CS or WS response pattern. In northern summer the warming and drying over parts of the Northern Hemisphere continents is larger in CS than in WS, due to a smaller net moisture flux from sea to land. The conclusions are: (1) climate predictions should be based on warm start experiments in order to obtain the best estimates of future changes; (2) ensemble means give predictions of regional changes which are statistically more robust than predictions from individual integrations. Note, however, that neither the removal of the cold start error nor the use of ensemble averaging can reduce uncertainties in the regional changes arising from model deficiencies, which remain considerable at the present stage of development. Received: 28 March 1997 / Accepted: 16 June 1997     

The increasing CO2 concentration in the atmosphere and its implication on agricultural productivity

The increasing concentration of CO₂ in the atmosphere should result in a general increase in the net primary productivity of most cultivated species and forest species, assuming no counterproductive climatic changes occur. The photosynthetic rate of C₃ plants is most responsive to increasing concentration of CO₂ in the ambient air. C₄ plants demonstrate a stomatal closure that causes reduced transpiration. In the case of both types of plants, the water use efficiency (photosynthesis/transpiration) is likely to be improved.It has been suggested that photosynthetic production may be limited today more by shortages of water and nutrients than by shortages of carbon dioxide. The author speculates that the inadvertant CO₂-fertilization now occurring could, in itself, cause a moderate release from these constraints.Physiological responses to an increased atmospheric CO₂ concentration are easily demonstrated in controlled environment studies. Because of the difficulty in maintaining artifically enriched air near the crop against the forces of turbulent transfer, studies in the open field have been inconclusive. The observation of decreased photosynthetic rate in a perennial crop during that part of the growing season when CO₂ concentration is naturally low suggests a technique by which it may be possible to infer what will happen in the real world of agricultural fields if a CO₂-rich environment, such as is predicted in the coming decades, materializes. Inferences from the very limited set of data available support the view that net photosynthetic production will be increased.Published as Paper No. 6123, Journal Series, Nebraska Agricultural Experiment Station. The work reported was conducted under Regional Research Project 11–33 and Nebraska Agricultural Experiment Station Project 1149.George Holmes Professor of Agricultural Meteorology, Center for Agricultural Meteorology and Climatology, Institute of Agriculture and Natural Sources, University of Nebraska-Lincoln, Lincoln, NE 68583, U.S.A.     

Effect of ocean thermal diffusivity on global warming induced by increasing atmospheric CO2

A global mean ocean model including atmospheric heating, heat capacity of the mixed layer ocean, and vertical thermal diffusivity in the lower ocean, proposed by Cess and Goldenberg (1981), is used in this paper to study the sen-sitivity of global warming to the vertical diffusivity. The results suggest that the behaviour of upper ocean tempera-ture is mainly determined by the magnitude of upper layer diffusivity and an ocean with a larger diffusivity leads to a less increase of sea surface temperature and a longer time delay for the global warming induced by increasing CO2 than that with smaller one. The global warming relative to four scenarios of CO2 emission assumed by Intergovernmental Panel of Climate Change (IPCC) is also estimated by using the model with two kinds of thermal diffusivities. The result shows that for various combinations of the CO2 emission scenarios and the diffusivities, the oceanic time delay to the global warming varies from 15 years to 70 years.     

The increasing CO2 concentration in the atmosphere and its implication on agricultural productivity II. Effects through CO2-induced climatic change

In a prior paper (Part I), the point was made that, assuming an unchanged climate, water use efficiency in agricultural crop production will likely be favored by the increase in CO₂ concentration projected to occur within the next half century. Since climatic changeis likely to result from the CO₂ concentration increase, its possible impacts on agricultural productivity must also be considered. An attempt to do so, using the Great Plains region of North America as a case study, is reported in this paper (Part II). A number of climatic models predict significant increases in surface temperature. Manabe and Wetherald's (1980) model provides the most specific projections for a hypothetical Northern hemisphere continent. That model also predicts an intensification of the hydrologic cycle with rainfall distribution altered so that some zones will receive more and some less as a result of a doubling in the atmospheric CO₂ concentration. The zone between 37 and 47° N latitude will suffer a reduction in availability of soil moisture. A number of regression models of grain yield as a function of temperature and precipitation have been used to anticipate the impacts of the projected climatic changes. The value of this approach is questioned. An alternative approach - the study of the migration of major agricultural crops across strong climatic gradients - is proposed. Changes in the geographical distribution of the hard red winter wheat zone in North America provide an example. The point is also made that factorscurrently limiting food production must be considered in order to predict the possible impacts of any given climatic change. In the central Great Plains today, the energy consumed by evapotranspiration often exceeds that supplied by net radiation since sensible heat advection from dryer regions to the south and west provides a major additional input of energy. If, as models project, the excess of precipitation over evaporation increases south of 37° N, the advection of sensible heat and, hence, the rates of evapotranspiration and degree of water stress on growing plants could be reduced in the adjacent regions to the north. Published as Paper No. 6123, Journal Series, Nebraska Agricultural Experiment Station. The work reported was conducted under Regional Research Project 11-033 and Nebraska Agricultural Station Project 11-049. George Holmes Professor of Agricultural Meteorology, Center for Agricultural Meteorology and Climatology, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, Nebraska, 68583-0728.     

The Present, Past, and Future Contributions to Global Warming of CO2 Emissions from Fuels

The objective of this paper is to emphasize theresponsibility of developed countries to implement the Climate Convention, as well as the role ofdeveloping countries in CO₂ emissions controlwhile sustaining their rights to increase energyconsumption per capita during the development process. Itis shown that the growth in CO₂$ emissions fromfossil fuel consumption in North America, excludingMexico, from 1990 to 1996 was 3.7 times higherthan that of Latin America in absolute terms. Thecumulative contribution to global warming, expressedas the mass of the gas multiplied by time (GtCy), can becalculated as the integration of the atmosphericconcentration of the emitted gas along time, witha weight function in the integrand to simulate theclimate response. To simulate climate response,we used the superposition of exponential decay functions with different decay constants. Thehistorical contributions of the OECD countries,the Eastern European countries and theex-Soviet Union, and from all developingcountries are considered. The future contributionsare computed in three scenarios. All of them showthat emissions from Non-Annex I countrieswill become higher than those of Annex I countriessoon after 2010, while the curves of atmosphericconcentration will cross one another later, not muchbefore 2050, and the respective contributions toglobal temperature increase will cross about 2090.     

The Relative Impact of Regional Scale Land Cover Change and Increasing CO2 over China

A series of 17-yr equilibrium simulations using the NCAR CCM3 (T42 resolution) were performed to investigate the regional scale impacts of land cover change and increasing CO2 over China. Simulations with natural and current land cover at CO2 levels of 280,355, 430, and 505 ppmv were conducted. Results show statistically significant changes in major climate fields (e.g. temperature and surface wind speed) on a 15-yr average following land cover change. We also found increases in the maximum temperature and in the diurnal temperature range due to land cover change. Increases in CO2 affect both the maximum and minimum temperature so that changes in the diurnal range are small. Both land cover change and CO2 change also impact the frequency distribution of precipitation with increasing CO2 tending to lead to more intense precipitation and land cover change leading to less intense precipitation-indeed, the impact of land cover change typically had the opposite effect versus the impacts of CO2. Our results provide support for the inclusion of future land cover change scenarios in long-term transitory climate inodelling experiments of the 21st Century. Our results also support the inclusion of land surface models that can represent future land cover changes resulting from an ecological response to natural climate variability or increasing CO2. Overall, we show that land cover change can have a significant impact on the regional scale climate of China, and that regionally, this impact is of a similar magnitude to increases in CO2 of up to about 430 ppmv. This means that that the impact of land cover change must be accounted for in detection and attribution studies over China.     

Global CO2 emissions trading: Early lessons from the U.S. acid rain program

The U.S. Environmental Protection Agency is implementing a program of SO₂ emission allowance trading as part of the Acid Rain Program authorized by the Clean Air Act Amendments of 1990. Electric utilities may use allowance trading as part of their compliance strategy to meet SO₂ emission reduction requirements, which begin in 1995. In the interest of a free market in emission credits, some utilities began trading in 1992. A strict but essential requirement for continuous-emissions monitoring was developed to support the trading program. This program is being widely watched and will be evaluated as part of an effort to determine if market concepts can be successfully extended to other environmental issues. One such issue is greenhouse gas emissions and their link with global warming and climate change. This paper focuses on the early lessons learned, issues, and challenges involved in going from a domestic electric utility SO₂ emissions trading program to inter-industry, inter-gas and international as well as national emissions trading and offsets programs. Prominent among these issues are CO₂ allowance allocations, equity, emissions monitoring, enforcement, and cost-effectiveness.Paper presented at the90th Annual Meeting of the Association of American Geographers, San Francisco, April 2, 1994, at the Air & Waste Management Association International Specialty Conference onGlobal Climate Change, Tempe, Arizona, April 8, 1994, and at a Cornell University Center for the Environment seminar on global climate change, April 25, 1994. I thank Michael Grubb, Joe Kruger, Elliot Lieberman, Brian McLean, Renee Rico, Richard Schuler and two anonymous referees for helpful comments on previous drafts of this paper. The views and opinions expressed herein are those of the author alone, and do not necessarily represent the policies of the U.S. Environmental Protection Agency.