Abstract: The Coupled Model Intercomparison Project (CMIP) collects output from global coupled ocean–atmosphere general circulation models (coupled GCMs) Among other uses, such models are employed both to detect anthropogenic effects in the climate record of the past century and to project future climatic changes due to human production of greenhouse gases and aerosols CMIP has archived output from both constant forcing (“control run”) and perturbed (1% per year increasing atmospheric carbon dioxide) simulations This report summarizes results form 18 CMIP models A third of the models refrain from employing ad hoc flux adjustments at the ocean–atmosphere interface The new generation of non-flux-adjusted control runs are nearly as stable as—and agree with observations nearly as well as—the flux-adjusted models Both flux-adjusted and non-flux-adjusted models simulate an overall level of natural internal climate variability that is within the bounds set by observations These developments represent significant progress in the state of the art of climate modeling since the Second (1995) Scientific Assessment Report of the Intergovernmental Panel on Climate Change (IPCC; see Gates et al [Gates, WL, et al, 1996 Climate models—Evaluation Climate Climate 1995: The Science of Climate Change, Houghton, JT, et al (Eds), Cambridge Univ Press, pp 229–284]) In the increasing-CO2 runs, differences between different models, while substantial, are not as great as one might expect from earlier assessments that relied on equilibrium climate sensitivity

Abstract: We report results from the highest-resolution simulations of global warming yet performed with an atmospheric general circulation model. We compare the climatic response to increased greenhouse gases of the National Center for Atmospheric Research (NCAR) climate model, CCM3, at T42 and T170 resolutions (horizontal grid spacing of 300 and 75 km respectively). All simulations use prescribed sea surface temperatures (SST). Simulations of the climate of 2100 ad use SSTs based on those from NCAR coupled model, Climate System Model (CSM). We find that the global climate sensitivity and large-scale patterns of climate change are similar at T42 and T170. However, there are important regional scale differences that arise due to better representation of topography and other factors at high resolution. Caution should be exercised in interpreting specific features in our results both because we have performed climate simulations using a single atmospheric general circulation model and because we used with prescribed sea surface temperatures rather than interactive ocean and sea-ice models.

Abstract: Consideration of abrupt climate change has generally been incorporated neither in analyses of climate–change impacts nor in the design of climate adaptation strategies. Yet the possibility of abrupt climate change triggered by human perturbation of the climate system is used to support the position of both those who urge stronger and earlier mitigative action than is currently being contemplated and those who argue that the unknowns in the Earth system are too large to justify such early action. This paper explores the question of abrupt climate change in terms of its potential implications for society, focusing on the UK and northwest Europe in particular. The nature of abrupt climate change and the different ways in which it has been defined and perceived are examined. Using the example of the collapse of the thermohaline circulation (THC), the suggested implications for society of abrupt climate change are reviewed; previous work has been largely speculative and has generally considered the implications only from economic and ecological perspectives. Some observations about the implications from a more social and behavioural science perspective are made. If abrupt climate change simply implies changes in the occurrence or intensity of extreme weather events, or an accelerated unidirectional change in climate, the design of adaptation to climate change can proceed within the existing paradigm, with appropriate adjustments. Limits to adaptation in some sectors or regions may be reached, and the costs of appropriate adaptive behaviour may be large, but strategy can develop on the basis of a predicted long–term unidirectional change in climate. It would be more challenging, however, if abrupt climate change implied a directional change in climate, as, for example, may well occur in northwest Europe following a collapse of the THC. There are two fundamental problems for society associated with such an outcome: first, the future changes in climate currently being anticipated and prepared for may reverse and, second, the probability of such a scenario occurring remains fundamentally unknown. The implications of both problems for climate policy and for decision making have not been researched. It is premature to argue therefore that abrupt climate change – in the sense referred to here – imposes unacceptable costs on society or the world economy, represents a catastrophic impact of climate change or constitutes a dangerous change in climate that should be avoided at all reasonable cost. We conclude by examining the implications of this contention for future research and policy formation.

Abstract: Weak sustainability is typically defined as non-declining utility, or perhaps non-declining production capacity. Weak sustainability places human welfare at the core, and substituting one source of welfare for another is not an issue (e.g., Pearce and Turner, 1990; Perman et al., 1999). As climate change is unlikely to reverse economic growth (Fankhauser and Tol, 2001; Tol, 1998), it is compatible with weak sustainability. However, climate change does pose an efficiency problem, as greenhouse gas emissions are externalities, and perhaps large ones (Pearce et al., 1996; Smith et al., 2001). Therefore, our first approach to measuring climate change is to estimate the marginal external costs of carbon dioxide emissions.

Abstract: International negotiations under the UN Framework Convention on Climate Change could take several different approaches to advance future mitigation commitments. Options range from trying to reach consensus on specific long-term atmospheric concentration targets (e.g. 550 ppmv) to simply ignoring this contentious issue and focusing instead on what can be done in the nearer term. This paper argues for a strategy that lies between these two extremes. Internationally agreed threshold levels for certain categories of impacts or of risks posed by climate change could be translated into acceptable levels of atmospheric concentrations. This could help to establish a range of upper limits for global emissions in the medium term that could set the ambition level for negotiations on expanded GHG mitigation commitments. The paper thus considers how physical and socio-economic indicators of climate change impacts might be used to guide the setting of such targets. In an effort to explore the feasibility and implications of low levels of stabilisation, it also quantifies an intermediate global emission target for 2020 that keeps open the option to stabilise at 450 ppmv CO2 If new efforts to reduce emissions are not forthcoming (e.g. the Kyoto Protocol or similar mitigation efforts fail), there is a significant chance that the option of 450 ppmv CO2 is out of reach as of 2020. Regardless of the preferred approach to shaping new international commitments on climate change, progress will require improved information on the avoided impacts climate change at different levels of mitigation and careful assessment of mitigation costs.

Abstract: Anthropogenic, or human-induced, climate change is a critical issue in science and in the affairs of humankind. Though the target of substantial research, the conclusions of climate change studies remain subject to numerous uncertainties. This article presents a very brief review of the basic arguments regarding anthropogenic climate change with particular emphasis on uncertainty.

Abstract: General circulation models (GCMs) that can simulate global climate are used to predict climate changes caused by an increase in atmospheric CO2 concentration. However, the spatial resolutions of currently running models are rough with a resolution of about 3° to 6° in latitude/longitude. Thus, reducing the relatively large-scale climatic states that the GCM provides to smaller-scale ones is required to evaluate impacts of climate changes on agriculture and natural ecosystems at local and regional scales. We constructed a dataset, namely the mesh climate change data of Japan, using the inverse distance weighted interpolation against coupled atmosphere-ocean GCMs’ (A-O GCMs) experiment results under gradually increasing atmospheric CO2 concentration. The A-O GCMs used in this article are ECHAM4/OPYC3 (Germany), CGCM1 (Canada), CSIRO-Mk2 (Australia), and CCSR/NIES (Japan). The dataset gives tha average climate change scenarios in Japan for every 10-year period over the next 100 years with a resolution of 7.5′ in longitude and 5′ in latitude (approximately 10 by 10 km). This article describes the construction method and contents of the dataset. In order to demonstrate the characteristics of the dataset, we examined the transient changes in spatial distribution of accumulated surface air temperature, accumulated precipitation, and mean short wave radiation during the months of May through September, corresponding with the major crop cultivation period in Japan.

Abstract: Palaeoclimatic data document a sensitive climate system subject to large and perhaps difficult-to-predict abrupt changes. These data suggest that neither the sensitivity nor the variability of the climate are fully captured in some climate-change projections, such as the Intergovernmental Panel on Climate Change (IPCC) Summary for Policymakers. Because larger, faster and less-expected climate changes can cause more problems for economies and ecosystems, the palaeoclimatic data suggest the hypothesis that the future may be more challenging than anticipated in ongoing policy making. Large changes have occurred repeatedly with little net forcing. Increasing carbon dioxide concentration appears to have globalized deglacial warming, with climate sensitivity near the upper end of values from general circulation models (GCMs) used to project human-enhanced greenhouse warming; data from the warm Cretaceous period suggest a similarly high climate sensitivity to CO(2). Abrupt climate changes of the most recent glacial-interglacial cycle occurred during warm as well as cold times, linked especially to changing North Atlantic freshwater fluxes. GCMs typically project greenhouse-gas-induced North Atlantic freshening and circulation changes with notable but not extreme consequences; however, such models often underestimate the magnitude, speed or extent of past changes. Targeted research to assess model uncertainties would help to test these hypotheses.

Abstract: The aim of this paper is to present a modeling framework for deriving emissions corridors that preserve the Atlantic thermohaline circulation (THC). The framework consists of a multi-gas reduced-form climate model coupled to a four-box THC model and allows for the main physical uncertainties (i.e., climate and North Atlantic hydrological sensitivity) to be taken into account. The emissions corridors are calculated along the conceptual and methodological lines of the tolerable windows approach (TWA). The corridor boundaries demarcate emissions limits for the 21 st century beyond which either the THC collapses or the mitigation burden becomes intolerable. Accordingly, the corridors represent the maneuvering space for climate policies committed to preserve the THC without endangering future economic growth. Results indicate a large dependence of the width of the emissions corridors on climate and North Atlantic hydrological sensitivity: for low values of climate and=or hydrological sensitivity the upper corridor boundary is far from being transgressed by any of the SRES emissions scenario for the 21 st century, while for high values of both quantities even low non-intervention scenarios leave the corridor.

Abstract: The first part of this thesis describes the further development of a dynamic global vegetation model, LPJ, and its application to selected scientific questions. LPJ has been extended to include isotopic fractionation of 13C at the leaf level during assimilation and includes a full isotopic terrestrial carbon cycle. Hence, it simulates the isotopic signature of the heterotrophic respiration fluxes. The model thus allows a quantitative analysis of the net biosphere exchange of CO2 and CO2 with the atmosphere as a function of changes in climate, land cover, atmospheric CO2, and the isotope ratio of CO2. The extended version of LPJ has been used to study the response of the global vegetation distribution to an abrupt climate change event (Younger Dryas) and the thereby incurred changes in the terrestrial carbon pools and fluxes and their isotopic 13C/12C ratio. Climate data from a 850-year-long coupled ocean-atmosphere general circulation model (ECHAM3/LSG) is used for these simulations. The comparison of the modelled vegetation distribution and shifts during this idealized Younger Dryas event with reconstructed vegetation maps for North America and Europe based on pollen records shows a reasonable agreement. The impact of the terrestrial carbon release during the Younger Dryas on the atmospheric CO2 and δ13C is analyzed using a simplified ocean model and compared to ice core measurements. In the standard case the simulation exhibits a significant change in global total terrestrial carbon stocks of about 180 Pg C leading to an atmospheric CO2 increase of ≈28 ppmv as a consequence of the climate change event. The robustness of the terrestrial signal during the Younger Dryas is studied by several sensitivity experiments concerning the initial values of the carbon pool sizes as well as the CO2 fertilization effect and the temperature dependency of the carbon decomposition rates. The resulting increase of atmospheric CO2 concentrations for the cold event varies between 16 to 33 ppmv among the different experiments. The simulated atmospheric δ13C values which are about 0.4 lower during the cold phase reflect major findings from ice core measurements and are fairly robust against the sensitivity experiments. The isotope version of LPJ has also been used to study the effects of climate variability, fire, and changes in land use on the exchange fluxes of CO2 and CO2 between the terrestrial biosphere and atmosphere for the last 100 years in greater detail. A transient, spatially explicit dataset of C4 crops and tropical C4 pastures has been compiled which, in combination with a land use scheme, allows the analysis of the impact of land use and C4 cultivation on the terrestrial stable isotope composition. LPJ simulates a global mean isotopic fractionation of 17.7 at the leaf level with interannual variations of ca. 0.3 in the case without land use for the years 1950 to 1998. In this case, interannual variability in the net CO2 flux between atmosphere and terrestrial biosphere is of the order of 15 Pg C yr−1. It is reduced to 4 Pg C yr−1 if the leaf-level fractionation factor is held constant at the long term mean. Depending on the chosen

Abstract: Climate change has become one of the most prominent global issues that affects the way in which large multinational fi rms (can) do business. The adoption of the Kyoto Protocol in the late 1990s marked a critical change in this respect. Before that date, most fi rms denied the effects of climate change and lobbied against government intervention and regulation. Currently though, the vast majority of multinationals no longer questions the reality of global climate change nor the risks that accompany it, but instead acknowledge the issue’s importance.

Abstract: A new version of the PAGE model, PAGE2002, has been developed and used to calculate the marginal impacts of CO2, CH4 and SF6 emissions. The main structural changes in PAGE2002 are the introduction of a third greenhouse gas and the incorporation of possible future large-scale discontinuities. The PAGE2002 model uses relatively simple equations to capture complex climatic and economic phenomena. This is justified because the results approximate those of the most complex climate simulations, and because all aspects of climate change are subject to profound uncertainty. To express the model results in terms of a single 'best guess' could be dangerously misleading. Instead, a range of possible outcomes should inform policy. PAGE2002 builds up probability distributions of results by representing 31 key inputs to the marginal impact calculations by probability distributions. In this investigation, PAGE2002 is run with global emissions of greenhouse gases from Scenario A2 of the IPCC. This scenario represents a heterogeneous world, with an underlying theme of self-reliance and preservation of local identities. As with all the IPCC illustrative scenarios, it assumes no active intervention to control emissions. The PAGE2002 mean results track the IPCC climate results very well. The range of results from the PAGE2002 model is larger than the range reported in the IPCC TAR. This is to be expected, as the IPCC results are simply the highest and lowest best guess results from the seven General Circulation Models considered by the IPCC, and not a true probability distribution. PAGE2002 gives the mean climate change impacts of scenario A2 over the next two centuries from 2000 to 2200 as US$26.3 trillion in year 2000 dollars, discounted back to 2000 at a pure time preference rate of 3% per year. The 5% and 95% points on the distribution are US$6.3 trillion and US$66.9 trillion. The marginal impact of each of the three gases, CO2, CH4 and SF6 is calculated by reducing the emissions of the gas by a small amount in the first analysis year, 2001, and finding the difference in impacts that this creates. The structure of the PAGE2002 model allows a probability distribution for the difference in impacts to be calculated. Market prices are about US$160 per tonne for methane and about US$25 000 per tonne for SF6. The climate change impacts of methane are a significant proportion of its market price. So a pipeline replacement to decrease losses could be justified if the Net Present Cost were less than about US$265 per tonne saved in 2000 US dollars - made up of not just US$160 from having the gas available to sell, but also US$105 from the reduction in climate change impacts. For SF6 the climate change impacts are much larger than the market price. The economics of schemes to reduce the leakage of SF6 are transformed once the climate change impacts are properly counted.

Abstract: : Most debates and studies addressing potential climate change have focused on the buildup of industrial greenhouse gases in the atmosphere and a gradual increase in global temperatures. But this "slow ramp" climate change scenario ignores recent and rapidly advancing evidence that Earth's climate repeatedly has become much colder, warmer, wetter, or drier-in time spans as short as three to 10 years. Earth's climate system appears to have sensitive thresholds, the crossing of which shifts the system into different modes of operation and triggers rapid, non-linear, and not necessarily global changes. This new paradigm of abrupt climate change does not appear to be on the radar screens of military planners, who treat climate change as a long term, low-level threat, with mostly sociological, not national security, implications. But intense and abrupt climate changes could escalate environmental issues into unanticipated security threats, and could compromise an unprepared military. The global ocean circulation system, often called the Ocean Conveyor, can change rapidly and shift the distribution patterns of heat and rainfall over large areas of the globe. The North Atlantic region is particularly vulnerable to abrupt regional coolings linked to ocean circulation changes. Global warming and ocean circulation changes also threaten the Arctic Ocean's sea ice cover. Beyond the abrupt climatic impacts, fundamental changes in ocean circulation also have immediate naval implications. Recent evidence suggests that the oceans already may be experiencing large-scale changes that could affect Earth's climate. Military planners should begin to consider potential abrupt climate change scenarios and their impacts on national defense.

Abstract: A major part of the international effort to understand climate change relates to predicting the distribution and magnitude of climate change impacts. Estimating long-term impacts has the dual source of uncertainty of, firstly, the prediction of the levels and types of emissions, and. secondly, the response of the global climate to these emissions. This chapter gives an overview of the causes and mechanisms of climate change, details the relationship between climate change and energy use in general and transport operations in particular, provides a background to international activity addressing climate change, and offers conclusions about the role of transport in the response to climate change.

Abstract: In this overview two definitions of climate are presented, from the meteorological point of view and from the climate system’s point of view. The origin of climate change is discussed, i.e., externally forced variability and free, or internal variability that is caused without external trigger by internal instabilities of the system. Both, forced and free variability can appear as periodic, randomly quasi-periodic, and abrupt climate change. Finally, various possibilities of climate forecast are considered.

Abstract: This paper presents an economy and climate model of 60 overlapping generations of finite lived agents and competitive firms interacting with a physical environment. Use of energy in production results in the release of carbon to the atmosphere which can affect global climate, and thus productivity. The model is calibrated to global economic activity over the 30 years ended in 1995. The model is solved using an Euler equation approach, and simulated for three climate change scenarios, capturing optimistic, median, and pessimistic predictions on the rate and severity of climate change in response to CO2 emissions. JEL classification: Q21; H23; L51

Abstract: Regional climate models can provide useful insights for research on water-sector adaptation to climate change. Results are presented from a RegCM2 study that investigates the effect of a doubling of atmospheric carbon dioxide upon climate for a domain centred over California. By the expected time of doubling, 2060, results show generally increasing surface temperatures, altered precipitation patterns, and reduced average annual snow accumulation. Two rankings of institutional scale – hierarchies of control and longevity before revision – are then presented to help identify appropriate directions for policy research. The goals are to: 1) tightly link possible adaptations with climate change impacts, and 2) match time-scales of climate change impacts with timescales of institutional change. Two examples of possible research programmes are identified: re-engineering north-coast river systems and securing southcoast water imports. Each research programme responds to the results of the RegCM2 study in terms of both the nature and the time-frame of the impacts.

Abstract: … what we are concerned with here is the fundamental interconnectedness of all things. Douglas Adams ( Dirk Gently's Holistic Detective Agency ) The wide range of data that can be exploited in the search for weather cycles must now be put in context. This database provides a considerable amount of information about the scale and time-span of a variety of meteorological variables. But to understand what insight, if any, these observed fluctuations provide about the overall cyclic behaviour of the weather, we need to look more closely at how the global climate functions. For only when the variability of the weather is analysed in terms of the processes that govern the global and regional energy balance of the Earth's climate is it possible to make a sensible assessment of the evidence of cycles. In particular, the possibility that all the ups and downs in the weather are nothing more than the natural variability of the complex non-linear connections between various components of the climate must be explored in detail. Once this issue has been examined it will be possible to focus on the more precise question of cyclic behaviour. This approach cannot go over all the standard climatological ground covered by text books (see the bibliography). Instead, it will concentrate on those features of the global climate that are apparently most closely linked with the fluctuations identified in Chapters 3 and 4.