Abstract: To prevent major global climate change all countries must begin to act now. However, there is no agreement on how rapidly greenhouse gases will be emitted over the next century, how rapidly they will accumulate in the atmosphere, what will be the cost of abatement, how large the climate change will be, or even whether the change will be predominantly beneficial or harmful. Beyond agreeing that greenhouse gases are likely to result in atmospheric warming, other factors held constant, there is no consensus on any of these questions.

Abstract: It is widely known that the concentration of greenhouse gases, particularly CO2, has increased steadily over the past quarter-century. Despite the fact that the radiative properties of such gases are rather well-understood, a clear consensus has yet to emerge among scientists as to the overall direction that global climate is evolving toward. Over the past decade, our understanding of the global climate system has advanced considerably with the development and application of increasingly sophisticated general circulation models (GCMs). In these models the dynamics, thermodynamics, radiative processes, and chemistry of the global climate system are represented to the maximum extent possible, given limitations in our understanding and computational capability.

Abstract: There is large public and political interest in the predictability of weather and climate, in particular in the influence of human activities on the likely climate change during the next century. Numerical models are the main tools which enable the nonlinear processes involved in the dynamics and physics of the atmosphere and other components of the climate system to be integrated in an effective way. The performance of such models used for weather forecasting has continued to improve as more accurate data with better coverage has become available, as improved descriptions of the physics and dynamics have been incorporated and as computing capacity and speed have increased. Studies of the predictability with models suggest that with further improvements in data and models deterministic forecasting of detailed weather may ultimately have useful skill up to 2-3 weeks ahead. Beyond the limit of deterministic forecasting, some skill remains for the forecasting of general weather patterns which can be pursued by studying ensembles of model forecasts from slightly varying initial conditions. The largest difficulty with further improvements of numerical models lies in their inadequate treatment of the motions too small to be explicitly resolved. Interactions between the atmosphere and the ocean are responsible for substantial variations on seasonal, interannual and longer timescales. Forecasts are being provided of seasonal precipitation in the Sahel region of Africa based on a knowledge of global sea surface temperature (SST) anomalies together with the assumption that such anomalies tend to persist from one season to the next. Attempts to forecast SST anomalies have centred on tropical regions in particular on the El Nino. Simple models show some skill in forecasting El Nino events 3-9 months in advance. Studies with more elaborate models which as yet only show partial success in simulating these events demonstrate the complex nature of the interactions involved. Turning to the likely changes in climate next century: if no changes occur in the atmosphere other than the increase in CO$\_{2}$ and other greenhouse gases due to human activities, the increase in radiative forcing due to a doubling of atmospheric CO$\_{2}$ concentration would lead to an increase of about 1.2 degrees C in global average temperature. Water vapour and ice-albedo feedbacks raise this to a figure of about 2.5 degrees C (with an uncertainty range of 1.5-4.5 degrees C) as estimated by the Inter-governmental Panel for Climate Change. Such a change would dominate over forcing likely to arise from other factors, and this estimated rate of change next century is probably greater than any which has occurred on earth during the past 10 000 years. The main uncertainties in climate change predictions arise from the inadequacies of the models in their descriptions of cloud-radiation and ocean circulation feedbacks. Until there is more confidence in the treatment of these feedbacks there are bound to be large uncertainties associated with any predictions of regional climate change. To reduce the uncertainties there need to be improvements in computer power, in model formulation and in our understanding of climate processes together with a large programme of observations of climate parameters to provide early detection of climate change and to provide validation of climate models and to provide data for initialization of model integrations. An important question is whether changes in climate due to changes in radiative forcing are predictable. It is pointed out that the response to climate over the past half million years to changes in forcing due to the variations in the Earth's orbit (Milankovitch cycles) is a regular one; some 60% of variations in the global temperature as established from the palaeontological record occur near frequencies of the Milankovitch cycles. We can, therefore, expect the changes in climate due to increasing greenhouse gases to be a largely predictable response. Large, but probably predictable, changes in the circulation of the deep ocean have modified climate change during past epochs and could have significant influence on future climate change.

Abstract: The greenhouse effect is accepted as an undisputed fact from both theoretical and observational considerations. In Earth's atmosphere, the primary greenhouse gas is water vapor. The specific concern today is that increasing concentrations of anthropogenically introduced greenhouse gases will, sooner or later, irreversibly alter the climate of Earth. Detecting climate change has been complicated by uncertainties in historical observations and measurements. Thus, the primary concern for the GEDEX project is how can climate change and enhanced greenhouse effects be unambiguously detected and quantified. Specifically examined are the areas of: Earth surface temperature; the free atmosphere (850 millibars and above); space-based measurements; measurement uncertainties; and modeling the observed temperature record.

Abstract: risks of global warming regardless of uncertainties about the response of the climate system . Scenario analyses conducted by EPA for a Report to Congress on Policy Options for Stabilizing Global Climate indicate that if no policies to limit greenhouse gas emissions are undertaken , the equivalent of a doubling of carbon dioxide would occur between 2030 and 2040 , and the Earth might be committed to a global warming of 2-4°C(3-7°F)by 2025 and 3-6°C(4-10°F) by 2050. Early application of existing and emergingtechnologies designed among other things, to increase the efficiency of energy use, expand the use of non-fossil energy sources , reverse deforestation, and phase out chlorofluorocarbons , could reduce the globalwarming commitment in 2025 by about one-fourth, and the rate of climatic change during the next century by at least 60%. A global commitment to rapidly reducing greenhouse gas emissions could stabilize the concentrations of these gases by the middle of the next century, perhaps limiting global warming to less than 2 °C (3 °F).

Abstract: This paper provides a concise evaluation of Dutch defense strategies against the threats of the sea-level rise as a consequence of global climate change. A set off external) event scenarios for the rise are described ranging from modest to dramatic. Four different policy response scenarios are presented, while their related costs are confronted with the threats of the event scenarios. It is concluded that, seen from a cost-effectiveness approach to various defense strategies, the traditional Dutch defense strategy is, for the time being, the most proper response to the sea-level rise.

Abstract: The oceans have a major influence on climate through the ocean-atmosphere exchange processes. However, limits to our present understanding of some of these processes is an important factor in our inability to model climate change precisely. Present knowledge of ocean structure and circulation is reviewed, with a particular emphasis on the Southern Hemisphere oceans, and the major ocean-atmosphere exchanges are examined. The influence of interhemispheric asymmetries in global warming scenarios is discussed. An improved understanding of the oceans and therefore better climate models will result from planned international ocean research experiments in the 1990s.

Abstract: The ocean plays a key role in the climate system of the earth. Its characteristics are so very different from those of the land that without it the earth’ s climate would be quite unlike the one we know. Because of the ocean, temperature ranges are very much reduced, particularly in regions not too remote from the coast. The large effective thermal capacity of the ocean causes the seasons to be delayed with respect to solar heating cycle. Because of ocean currents, some regions are warmer and others colder than they would otherwise be.

Abstract: Chapter 1.1 A Target-based, Least-cost Approach to Climate Stabilization A. Introduction B. Growing Awareness of the Climate Threat C. Driving Forces of Climate Change D. Greenhouse Risks and Consequences: Just Warmer Weather? E. Analytic Framework for the Prevention Paradigm Chapter 1.2 Is Climate Stabilization still Feasible? A. Overview B. Climate Modeling Approach C. How Much Warming is Already Locked in from the Past? D. What Further Warming will Future Emissions Bring? E. From Concentration Ceilings to Policy Targets Chapter 1.3 Control Requirements for Non-fossil Greenhouse Gases A. Overview B. CFC Releases and Other Urban-Industrial Emissions C. Greenhouse Gases and Agriculture D. Carbon Releases from Deforestation and Soil Destruction: How Significant Are they in Climate Warming? E. Restoring Biospheric Carbon Pools in Forests and Soils Chapter 1.4 How much Fossil Fuel can still be Burned? A. Overview B. Concentration Limit for Carbon Dioxide C. Fossil Reserves, Energy Content, Carbon Content, and Airborne Fraction D. Global Fossil Carbon Budget Chapter 1.5 How could the Global Carbon Budget be Shared? A. Climate Change and Global Equity B. How Could Equity Goals Be Quantified? C. Fossil Carbon Emissions and Interregional Equity: The Record to Date D. Equity-based Allocation of the Global Carbon Budget E. Person-year Equity and Compensatory International Assistance Chapter 1.6 How Quickly must Fossil Fuels be Phased Out? Global and Regional Milestones A. Introduction B. What Rates of Fossil Phase-out Could Be Viable? C. Milestones for the Global Fossil Phase-out D. Are There Any Other Options? E. C/GDP Ratios: Historic versus Required Future Changes F. Summary and Conclusions Chapter 1.7 A Global Compact on Climate Stabilization and Sustainable Development A. Climate Stabilization and Sustainable Development B. International Protocols versus Leadership by Example C. The Climate Convention D. Fossil Fuel Protocol E. Protocol on Reforestation and Agricultural Land-Use F. Protocol on Chlorofluorocarbons G. Protocol on Other Trace Gases H. Conclusion APPENDIX 1.1 APPENDIX 1.2