An analogue model to derive additional climate change scenarios from existing GCM simulations

 Changes in land surface driving variables, predicted by GCM transient climate change experiments, are confirmed to exhibit linearity in the global mean land temperature anomaly, ΔT _l . The associated constants of proportionality retain spatial and seasonal characteristics of the GCM output, whilst ΔT _l is related to radiative forcing anomalies. The resultant analogue model is shown to be robust between GCM runs and as such provides a computationally efficient technique of extending existing GCM experiments to a large range of climate change scenarios. As an example impacts study, the analogue model is used to drive a terrestrial ecosystem model, and predicted changes in terrestrial carbon are found to be similar to those when using GCM anomalies directly. Received: 4 January 1999 / Accepted: 11 December 1999     

Thinking globally and siting locally – renewable energy and biodiversity in a rapidly warming world

Increasing greenhouse gas emissions are projected to raise global average surface temperatures by 3?–4 °C within this century, dramatically increasing the extinction risk for terrestrial and freshwater species and severely disrupting ecosystems across the globe. Limiting the magnitude of warming and its devastating impacts on biodiversity will require deep emissions reductions that include the rapid, large-scale deployment of low-carbon renewable energy. Concerns about potential adverse impacts to species and ecosystems from the expansion of renewable energy development will play an important role in determining the pace and scale of emissions reductions and hence, the impact of climate change on global biodiversity. Efforts are underway to reduce uncertainty regarding wildlife impacts from renewable energy development, but such uncertainty cannot be eliminated. We argue the need to accept some and perhaps substantial risk of impacts to wildlife from renewable energy development in order to limit the far greater risks to biodiversity loss owing to climate change. We propose a path forward for better reconciling expedited renewable energy development with wildlife conservation in a warming world.     

Uncertainties in projected impacts of climate change on European agriculture and terrestrial ecosystems based on scenarios from regional climate models

The uncertainties and sources of variation in projected impacts of climate change on agriculture and terrestrial ecosystems depend not only on the emission scenarios and climate models used for projecting future climates, but also on the impact models used, and the local soil and climatic conditions of the managed or unmanaged ecosystems under study. We addressed these uncertainties by applying different impact models at site, regional and continental scales, and by separating the variation in simulated relative changes in ecosystem performance into the different sources of uncertainty and variation using analyses of variance. The crop and ecosystem models used output from a range of global and regional climate models (GCMs and RCMs) projecting climate change over Europe between 1961–1990 and 2071–2100 under the IPCC SRES scenarios. The projected impacts on productivity of crops and ecosystems included the direct effects of increased CO₂ concentration on photosynthesis. The variation in simulated results attributed to differences between the climate models were, in all cases, smaller than the variation attributed to either emission scenarios or local conditions. The methods used for applying the climate model outputs played a larger role than the choice of the GCM or RCM. The thermal suitability for grain maize cultivation in Europe was estimated to expand by 30–50% across all SRES emissions scenarios. Strong increases in net primary productivity (NPP) (35–54%) were projected in northern European ecosystems as a result of a longer growing season and higher CO₂ concentrations. Changing water balance dominated the projected responses of southern European ecosystems, with NPP declining or increasing only slightly relative to present-day conditions. Both site and continental scale models showed large increases in yield of rain-fed winter wheat for northern Europe, with smaller increases or even decreases in southern Europe. Site-based, regional and continental scale models showed large spatial variations in the response of nitrate leaching from winter wheat cultivation to projected climate change due to strong interactions with soils and climate. The variation in simulated impacts was smaller between scenarios based on RCMs nested within the same GCM than between scenarios based on different GCMs or between emission scenarios.     

Impacts of thermohaline circulation shutdown in the twenty-first century

We discuss climate impacts of a hypothetical shutdown of the thermohaline circulation (‘THC’) in the 2050s, using the climate model HadCM3. Previous studies have generally focussed on the effects on pre-industrial climate. Here we take into account increased greenhouse gas concentrations according to an IS92a emissions scenario. THC shutdown causes cooling of the Northern Hemisphere of -1.7?C, locally stronger. Over western Europe cooling is strong enough for a return to pre-industrial conditions and a significant increase in the occurrence of frost and snow cover. Global warming restricts the increase in sea ice cover after THC shutdown. This lessens the amount of cooling over NW Europe, but increases it over North America, compared to pre-industrial shutdown. This reflects a non-linearity in the local temperature response to THC shutdown. Precipitation change after THC shutdown is generally opposite to that caused by global warming, except in western and southern Europe, where summer drying is enhanced, and in Central America and southeast Asia, where precipitation is also further reduced. Local rise in sea level after THC shutdown can be large along Atlantic coasts (pm; 25,cm), which would add to the rise caused by global warming. Potentially rapid THC shutdown adds to the range of uncertainty of projected future climate change.     

Climate change scenarios for global impacts studies

We describe a set of global climate change scenarios that have been used in a series of studies investigating the global impacts of climate change on several environmental systems and resources — ecosystems, food security, water resources, malaria and coastal flooding. These scenarios derive from modelling experiments completed by the Hadley Centre over the last four years using successive versions of their coupled ocean–atmosphere global climate model. The scenarios benefit from ensemble simulations (made using HadCM2) and from an un-flux-corrected experiment (made using HadCM3), but consider only the effects of increasing greenhouse gas concentrations. The effects of associated changes in sulphate aerosol concentrations are not considered. The scenarios are presented for three future time periods — 30-year means centred on the 2020s, the 2050s and the 2080s — and are expressed with respect to the mean 1961–1990 climate. A global land observed climatology at 0.5° latitude/longitude resolution is used to describe current climate. Other scenario variables — atmospheric CO₂ concentrations, global-mean sea-level rise and non-climatic assumptions relating to population and economy — are also provided. We discuss the limitations of the created scenarios and in particular draw attention to sources of uncertainty that we have not fully sampled.     

The modification of greenhouse gas warming by the direct effect of sulphate aerosols

 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     

IPCC《全球1.5℃增暖特别报告》冰冻圈变化及其影响解读

在气候系统五大圈层中,冰冻圈对气候变化高度敏感,近几十年来气候变暖已引起全球冰川、冻土、积雪和海冰等冰冻圈要素加速退缩,进而对区域水资源、生态环境、社会经济发展和人类福祉产生了深远影响。2018年10月,IPCC在韩国仁川公布了《全球1.5℃增暖特别报告》（SR1.5）。报告较系统地呈现了关于全球1.5℃温升目标的基本科学认知,并探讨了可持续发展及消除贫困目标下加强全球响应的路径。在冰冻圈相关内容方面,报告呈现了有关全球1.5℃和2℃温升下冰冻圈（主要是海冰和多年冻土）变化及其对大气圈、水圈、生物圈、岩石圈和人类圈影响的一些亮点结论,还关注了全球1.5℃和2℃温升下冰冻圈相关的气候变化热点（区）和地球系统临界因素。报告指出,随着温度不断升高,冰冻圈及其相关要素和热点（区）面临的风险将不断增加,但将全球温升控制在1.5℃而不是2℃或更高时的风险将大大降低。     

Intensification of seasonal extremes given a 2°C global warming target

Current international efforts to reduce greenhouse gas emissions and limit human-induced global-mean near-surface temperature increases to 2°C, relative to the pre-industrial era, are intended to avoid possibly significant and dangerous impacts to physical, biological, and socio-economic systems. However, it is unknown how these various systems will respond to such a temperature increase because their relevant spatial scales are much different than those represented by numerical global climate models—the standard tool for climate change studies. This deficiency can be addressed by using higher-resolution regional climate models, but at great computational expense. The research presented here seeks to determine how a 2°C global-mean temperature increase might change the frequency of seasonal temperature extremes, both in the United States and around the globe, without necessarily resorting to these computationally-intensive model experiments. Results indicate that in many locations the regional temperature increases that accompany a 2°C increase in global mean temperatures are significantly larger than the interannual-to-decadal variations in seasonal-mean temperatures; in these locations a 2°C global mean temperature increase results in seasonal-mean temperatures that consistently exceed the most extreme values experienced during the second half of the 20th Century. Further, results indicate that many tropical regions, despite having relatively modest overall temperature increases, will have the most substantial increase in number of hot extremes. These results highlight that extremes very well could become the norm, even given the 2°C temperature increase target.     

Development of a risk-hedging CO2-emission policy, part I: Risks of unrestrained emissions

A rational global strategy with respect to greenhouse-gas emissions would seek to minimize total risk, which is the sum of the risk of negative impacts due to climatic change associated with a given level of emissions, and the risks associated with the process of achieving that emission level. Given the existence of reducible uncertainties in estimating these risks, and the possibility that an emission target thought to minimize total risk is later found to be not strict enough, a risk-hedging strategy is a more realistic policy objective. This paper is Part I of a two-part series in which these risks are reviewed and an interim risk-hedging emission level is proposed. Here, the risks associated with unrestrained greenhouse-gas emissions are reviewed. In particular, the carbon-cycle response to continuing CO₂ emissions; the heat trapping of projected greenhouse gas increases in comparison to other anthropogenic and natural heating or cooling perturbations; the climatic response to heating perturbations; and the impacts of projected climatic change on global agriculture, forests, coastal regions, coral reefs, water resources, terrestrial species, stratospheric and tropospheric ozone, and human comfort and welfare are critically examined. It is concluded that unrestrained emissions of greenhouse gases pose real and substantial risks to human societies and to ecosystems, and that these risks are likely to grow substantially if the climate warms beyond that associated with a CO₂ doubling. These risks clearly justify some action to limit emissions. The magnitude of emission restraint that is justified depends not only on the risks reviewed here, but also on the risks associated with measures to limit greenhouse-gas emissions, which are reviewed in Part II.     

The RCP greenhouse gas concentrations and their extensions from 1765 to 2300

We present the greenhouse gas concentrations for the Representative Concentration Pathways (RCPs) and their extensions beyond 2100, the Extended Concentration Pathways (ECPs). These projections include all major anthropogenic greenhouse gases and are a result of a multi-year effort to produce new scenarios for climate change research. We combine a suite of atmospheric concentration observations and emissions estimates for greenhouse gases (GHGs) through the historical period (1750?C2005) with harmonized emissions projected by four different Integrated Assessment Models for 2005?C2100. As concentrations are somewhat dependent on the future climate itself (due to climate feedbacks in the carbon and other gas cycles), we emulate median response characteristics of models assessed in the IPCC Fourth Assessment Report using the reduced-complexity carbon cycle climate model MAGICC6. Projected ??best-estimate?? global-mean surface temperature increases (using inter alia a climate sensitivity of 3°C) range from 1.5°C by 2100 for the lowest of the four RCPs, called both RCP3-PD and RCP2.6, to 4.5°C for the highest one, RCP8.5, relative to pre-industrial levels. Beyond 2100, we present the ECPs that are simple extensions of the RCPs, based on the assumption of either smoothly stabilizing concentrations or constant emissions: For example, the lower RCP2.6 pathway represents a strong mitigation scenario and is extended by assuming constant emissions after 2100 (including net negative CO₂ emissions), leading to CO₂ concentrations returning to 360 ppm by 2300. We also present the GHG concentrations for one supplementary extension, which illustrates the stringent emissions implications of attempting to go back to ECP4.5 concentration levels by 2250 after emissions during the 21^st century followed the higher RCP6 scenario. Corresponding radiative forcing values are presented for the RCP and ECPs.     

Evaluation of Haney-Type Surface ThermalBoundary Conditions Using a CoupledAtmosphere and Ocean Model

A coupled atmosphere-ocean model developed at the Institute for Space Studies at NASA Goddard Space Flight Center (Russell et al., 1995) was used to verify the validity of Haney-type surface thermal boundary condition, which linearly connects net downward surface heat flux Q to air / sea temperature difference △T by a relaxation coefficient k. The model was initiated from the National Centers for Environmental Prediction (NCEP) atmospheric observations for 1 December 1977, and from the National Ocean Data Center (NODC) global climatological mean December temperature and salinity fields at 1° ×1° resolution. The time step is 7.5 minutes. We integrated the model for 450 days and obtained a complete model-generated global data set of daily mean downward net surface flux Q, surface air temperature TA,and sea surface temperature To. Then, we calculated the cross-correlation coefficients (CCC) between Q and △T. The ensemble mean CCC fields show (a) no correlation between Q and △T in the equatorial regions, and (b) evident correlation (CCC≥ 0.7) between Q and △T in the middle and high latitudes.Additionally, we did the variance analysis and found that when k= 120 W m-2K-1, the two standard deviations, σQ and σk△T, are quite close in the middle and high latitudes. These results agree quite well with a previous research (Chu et al., 1998) on analyzing the NCEP re-analyzed surface data, except that a smaller value of k (80 W m-2K-1) was found in the previous study.     

Modelling the equilibrium and transient responses of global temperature to past and future trace gas concentrations

Recent works with energy balance climate models and oceanic general circulation models have assessed the potential role of the world ocean for climatic changes on a decadal to secular time scale. This scientific challenge is illustrated by estimating the response of the global temperature to changes in trace gas concentration from the pre-industrial epoch to the middle of the next century. A simple energetic formulation is given to estimate the effect on global equilibrium temperature of a fixed instantaneous radiative forcing and of a time-dependent radiative forcing. An atmospheric energy balance model couple to a box-advection-diffusion ocean model is then used to estimate the past and future global climalic transient response to trace-gas concentration changes. The time-dependent radiative perturbation is estimated from a revised approximate radiative parameterization, and the recent reference set of trace gas scenarios proposed by Wuebbles et al. (1984) are adopted as standard scenarios. Similar computations for the past and future have recently been undertaken by Wigley (1985), but using a purely diffusive ocean and slightly different trace gas scenarios. The skill of the socalled standard experiment is finally assessed by examining the model sensitivity of different parameters such as the equilibrium surface air temperature change for a doubled CO₂ concentration [T _ae (2×CO₂)], the heat exchange with the deeper ocean and the trace gas scenarios. For T _ae (2×CO₂) between 1 K and 5 K, the following main results are obtained: (i) for a pre-industrial CO₂, concentration of 270 ppmv, the surface air warming between 1850 and 1980 ranges between 0.4 and 1.4 K (if a pre-industrial CO₂ concentration of 290 ppmv is chosen, the range is between 0.3 and 1 K); (ii) by comparison with the instantaneous equilibrium computations, the deeper ocean inertia induces a delay which amounts to between 6 years [for lower T _ae (2×CO₂)] and 23 years [for higher Tae(2×CO₂)] in 1980; (iii) for the standard future CO₂ and other trace gas scenarios of Wuebbles et al., the surface air warming between 1980 and 2050 is calculated to range between 0.9 and 3.4 K, with a delay amounting to between 7 years and 32 years in 2050 when compared to equilibrium computations.     

Observed and projected climate change in Taiwan

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     

The impacts avoided with a 1.5 °C climate target: a global and regional assessment

The 2015 Paris Agreement commits countries to pursue efforts to limit the increase in global mean temperature to 1.5 °C above pre-industrial levels. We assess the consequences of achieving this target in 2100 for the impacts that are avoided, using several indicators of impact (exposure to drought, river flooding, heat waves and demands for heating and cooling energy). The proportion of impacts that are avoided is not simply equal to the proportional reduction in temperature. At the global scale, the median proportion of projected impacts avoided by the 1.5 °C target relative to a rise of 4 °C ranges between 62 and 95% across sectors: the greatest reduction is for heat wave impacts. The 1.5 °C target results in impacts that would be between 27 and 62% lower than with the 2 °C target. For each indicator, there are differences in the proportions of impacts avoided between regions depending on exposure and the regional changes in climate (particularly precipitation). Uncertainty in the proportion of impacts that are avoided for a specific sector depends on the range in the shape of the relationship between global temperature change and impact, and this varies between sectors.     

Assessing the strength of regional changes in near-surface climate associated with a global warming of 2°C

In this study, the strength of the regional changes in near-surface climate associated with a global warming of 2°C with respect to pre-industrial times is assessed, distinguishing between 26 different regions. Also, the strength of these regional climate changes is compared to the strength of the respective changes associated with a markedly stronger global warming of 4.5°C. The magnitude of the regional changes in climate is estimated by means of a normalized regional climate change index, which considers changes in the mean as well as changes in the interannual variability of both near-surface temperature and precipitation. The study is based on two sets of four ensemble simulations with the ECHAM5/MPI-OM coupled climate model, each starting from different initial conditions. In one set of simulations (1860–2200), the greenhouse gas concentrations and sulphate aerosol load have been prescribed according to observations until 2000 and according to the SRES A1B scenario after 2000. In the other set of simulations (2020–2200), the greenhouse gas concentrations and sulphate aerosol load have been prescribed in such a way that the simulated global warming does not exceed 2°C with respect to pre-industrial times. The study reveals the strongest changes in near-surface climate in the same regions for both scenarios, i.e., the Sahara, Northern Australia, Southern Australia and Amazonia. The regions with the weakest changes in near-surface climate, on the other hand, vary somewhat between the two scenarios except for Western North America and Southern South America, where both scenarios show rather weak changes. The comparison between the magnitude of the regional changes in near-surface climate for the two scenarios reveals relatively strong changes in the 2°C-stabilization scenario at high northern latitudes, i.e., Northeastern Europe, Alaska and Greenland, and in Amazonia. Relatively weak regional climate changes in this scenario, on the other hand, are found for Eastern Asia, Central America, Central South America and Southern South America. The ratios between the regional changes in the near-surface climate for the two scenarios vary considerably between different regions. This illustrates a limitation of obtaining regional changes in near-surface climate associated with a particular scenario by means of scaling the regional changes obtained from a widely used “standard” scenario with the ratio of the changes in the global mean temperature projected by these two scenarios.     

Impact of non-outbreak insect damage on vegetation in northern Europe will be greater than expected during a changing climate

Background insect herbivory, in addition to insect outbreaks, can have an important long term influence on the performance of tree species. Since a projected warmer climate may favour insect herbivores, we use a dynamic ecosystem model to investigate the impacts of background herbivory on vegetation growth and productivity, as well as distribution and associated changes in terrestrial ecosystems of northern Europe. We used the GUESS ecosystem modelling framework and a simple linear model for including the leaf area loss of Betula pubescens in relation to mean July temperature. We tested the sensitivity of the responses of the simulated ecosystems to different, but realistic, degrees of insect damage. Predicted temperature increases are likely to enhance the potential insect impacts on vegetation. The impacts are strongest in the eastern areas, where potential insect damage to B. pubescens can increase by 4–5%. The increase in insect damage to B. pubescens results in a reduction of total birch leaf area (LAI), total birch biomass and birch productivity (Net Primary Production). This effect is stronger than the insect damage to leaf area alone would suggest, due to its second order effect on the competition between tree species. The model's demonstration that background herbivory may cause changes in vegetation structure suggests that insect damage, generally neglected by vegetation models, can change predictions of future forest composition. Carbon fluxes and albedo are only slightly influenced by background insect herbivory, indicating that background insect damage is of minor importance for estimating the feedback of terrestrial ecosystems to climate change.     

Near-term increase in frequency of seasonal temperature extremes prior to the 2°C global warming target

Given current international efforts to reduce greenhouse gas emissions and limit human-induced global-mean near-surface temperature increases to 2°C, relative to the pre-industrial era, we seek to determine the impact such a temperature increase might have upon the frequency of seasonal-mean temperature extremes; further we seek to determine what global-mean temperature increase would prevent extreme temperature values from becoming the norm. Results indicate that given a 2°C global mean temperature increase it is expected that for 70–80% of the land surface maximum seasonal-mean temperatures will exceed historical extremes (as determined from the 95th percentile threshold value over the second half of the 20th Century) in at least half of all years, i.e. the current historical extreme values will effectively become the norm. Many regions of the globe—including much of Africa, the southeastern and central portions of Asia, Indonesia, and the Amazon—will reach this point given the “committed” future global-mean temperature increase of 0.6°C (1.4°C relative to the pre-industrial era) and 50% of the land surface will reach it given a future global-mean temperature increase of between 0.8 and 0.95°C (1.6–1.75°C relative to the pre-industrial era). These results suggest substantial fractions of the globe could experience seasonal-mean temperature extremes with high regularity, even if the global-mean temperature increase remains below the 2°C target.     

全球气候变化对中国森林生态系统的影响

人类活动所引起的温室效应及由此造成的全球气候变化和对全球生态环境的影响正引起人们越来越多的重视.作为全球陆地生态系统一个重要组分,中国的森林生态系统对未来全球气候变化的响应更是人们关注的重点.作者系统地总结了全球气候变化对中国森林生态系统分布、生态系统生产力、森林树种以及森林土壤的影响,指出了现阶段该领域研究中存在的一些问题,并对今后需要加强的一些核心问题与研究重点作了展望.     

极端天气气候事件变化对荒漠化、土地退化和粮食安全的影响

土地是人类赖以生存的重要资源,在受气候变化影响的同时其状况变化也在气候系统中起着关键作用。IPCC最新发布的气候变化与土地特别报告（SRCCL）系统反映了关于荒漠化、土地退化、可持续土地管理、粮食安全和陆地生态系统碳通量方面的最新科学认知,并探讨了如何进行更加可持续性的土地利用和管理以应对与土地相关的气候变化问题。文中从极端事件变化及其影响的角度,结合SRCCL与其他相关文献,予以分析和总结。结果表明,在全球变暖的背景下,极端天气气候事件的变化已经并将继续影响荒漠化和土地退化进程并对粮食安全造成冲击;而土地对气候系统的反馈作用,又会加剧气候变化并提高极端事件发生的概率和严重程度。面对气候变化尤其是极端事件给土地带来的巨大压力,必须坚持可持续的土地管理,通过减少包括土地和粮食系统在内的所有行业的排放,才有可能实现到21世纪末将全球平均升温控制在相对工业化前水平2℃以内的目标,以减轻气候变化对土地和粮食系统的负面影响。     

The Canadian Centre for Climate Modelling and Analysis global coupled model and its climate

 A global, three-dimensional climate model, developed by coupling the CCCma second-generation atmospheric general circulation model (GCM2) to a version of the GFDL modular ocean model (MOM1), forms the basis for extended simulations of past, current and projected future climate. The spin-up and coupling procedures are described, as is the resulting climate based on a 200 year model simulation with constant atmospheric composition and external forcing. The simulated climate is systematically compared to available observations in terms of mean climate quantities and their spatial patterns, temporal variability, and regional behavior. Such comparison demonstrates a generally successful reproduction of the broad features of mean climate quantities, albeit with local discrepancies. Variability is generally well-simulated over land, but somewhat underestimated in the tropical ocean and the extratropical storm-track regions. The modelled climate state shows only small trends, indicating a reasonable level of balance at the surface, which is achieved in part by the use of heat and freshwater flux adjustments. The control simulation provides a basis against which to compare simulated climate change due to historical and projected greenhouse gas and aerosol forcing as described in companion publications. Received: 24 September 1998 / Accepted: 8 October 1999