The Atmospheric Sciences Entering the Twenty-First Century (1998) / Chapter Skim
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5 Climate and Climate Change Research Entering the Twenty-First Century
5 Climate and Climate Change Research Entering the Twenty-First Century
Pages 272-324
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The objectives are to understand the mechanisms of natural climate variability on time scales of seasons to centuries and to assess their predictability, to predict the future response of the 1Report of the Climate Research Committee: E.J. Barron (Chair)
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Current model projections based on increases in greenhouse gases and aerosols and on land cover change indicate the potential for large, and rapid, climate change relative to the historical and paleoclimatic records, with concomitantly large influences on human activities and ecosystems. Although remarkable progress in developing these climate models has occurred over the past two decades, current climate models are characterized by a great number of uncertainties.
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· Focus on key opportunities for reducing major uncertainties in climate models, including improved observations of water vapor.
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· Focus on key opportunities for reducing major uncertainties in climate models, including greater understanding of climate-water vapor feedbacks and improved representation of atmospheric chemistry and indirect chemistry-climate interactions.
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INTRODUCTION Three general categories of climate variability and change have been adopted by the World Climate Research Programme: seasonal-to-interannual climate variability, decadal-to-centennial climate variability, and changes in global climate induced by the aggregate of human activities that change both the concentrations of greenhouse gases and aerosols in the atmosphere and the pattern of vegetative land cover. Humans, as individuals and societies, and ecosystems are affected by and respond to each of these three categories of variability and change.
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From page 277... ...
Climate variability on these time scales has produced marked shifts in human wellbeing recorded in history over the past several centuries and can be expected to result in significant economic and human dislocations in the future. Current climate model projections based on anthropogenic increases in greenhouse gases and land cover changes indicate the potential for large, and rapid, climate change relative to the historical and paleoclimatic records, with concomitantly large influences on human activities and ecosystems.
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Large gaps in our knowledge of interannual and decade-tocentury natural variability hinder our ability to provide credible predictive skill or to distinguish the role of human activities from natural variability. Narrowing these uncertainties and applying our understanding define the mission of climate and climate change research and education for the twenty-first century.
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, to enhance and analyze observations, conduct process studies, and improve climate models. The principal goal has been to develop credible methods to predict climate variability and change.
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280 so o 7 \ ~ Char ,~ ~ - ' D ~ <7~< ~, _, ~ ~ l ~ .= so _ ~ o ~ A ~ .o Cal O O ~ V: o V C~]
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in real time allows an unprecedented look at the state of the atmosphere, sea surface and subsurface tropical Pacific in real time (McPhaden et al., 1998~.
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in the eastern to central tropical Pacific as much as a year in advance (Figure II.5.3) (Latif et al., 1994, 1998~.
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Efforts to document and understand natural climate variability on time scales of decades to centuries provide important insights for climate research in the twenty-first century: 1. Analyses of historical records illustrate a number of interesting cases of longer period fluctuations for North America including (a)
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4. Concerted efforts have resulted in long records of natural variability (e.g., 200,000-year records from ice cores and a greater than 1,000-year record from tree rings)
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CLIMATE AND CLIMATE CHANGE 'SoLm art..
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7. Climate model studies suggest that the feedbacks between land surface characteristics and the atmosphere may also be significant factors in decadalscale variability (e.g., prolonged Sahel drought)
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SOURCE: After Minnis et al., 1993; updated by Minnis, 1994. models' predictive capability.
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., ,1''\ ~ ',",''1 ~ \N, - -- Model Observations 1- A
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Research in the twentieth century has elucidated much of the complexity of natural variability and has begun to document its scope. These results demonstrate the importance of additional research to reduce the uncertainties associated with detecting and projecting future climate change.
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3. Improved representation of the land surface in climate models from early parameterizations of specified albedo, emissivity, and simple "bucket" hydrology to fully coupled biosphere-atmosphere transfer schemes with multiple soil layers has served to demonstrate that changes in the land surface with land use change, and through vegetation-climate feedbacks, can be significant because of their impact on energy, moisture, and greenhouse gas fluxes.
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Observational estimates are from ERBE data for 1985-1988. Climate simulations completed by participants in AMIP were carried out with sea surface temperatures prescribed for 1979 through 1988.
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10. In addition to the improved recognition and documentation of the scope of natural variability, comparison of paleoclimatic data and model experiments suggests a range of climate sensitivity in geologic history to a variety of climatic forcing factors, including carbon dioxide, which is very similar to the range given by the Intergovernmental Panel on Climate Change (IPCC)
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293 my' I ~ ~ ID Abed o to .
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The foundation of this strategy must be based on addressing key scientific questions: · What is the nature of global and regional climate variability on seasonalto-decadal and longer time scales? What are the spatial and temporal characteristics of this variability?
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Berz, 1998. Key Drivers for Research in the Twenty-First Century The observations and the insights derived from the twentieth century can be used to describe the impetus for climate and climate change research entering the twenty-first century.
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is associated with widely distributed weather anomalies and sometimes severe conditions, which are characterized by significant economic and human dislocations. Tropical Pacific sea surface temperature (SST)
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Paleoclimatic records indicate that the magnitude of regional and global variability can exceed observed interannual variations that are known to result in significant human and economic dislocations. · Improved knowledge of the coupled Earth system will increase understanding of natural variability on all time scales and lead to a greater realization of the practical benefits of enhanced predictive capability.
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Current climate models provide the most comprehensive projections of the magnitude and timing of climate change associated with increases in greenhouse gases and aerosols. The range of model experiments and their assessment by the IPCC suggest that global mean surface temperature will increase by about 0.9 to 3.5°C by the end of the twenty-first century.
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, and improvements in climate models over the past two decades strongly suggest that enhanced predictive capability will occur as a result of increased knowledge of the coupled Earth system. Just as interannual-to-seasonal forecasts have considerable economic value, increased predictive capability on longer time scales is likely to have a positive impact on economic vitality and economic security.
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For each objective, we can articulate a list of requirements based on experience from past successes and failures, from the remaining uncertainties and areas of scientific debate, and from reasoned assessment of the opportunities to promote significant advancement in climate and climate change research. Objective 1 Stop the deterioration and improve current observational capability as a first step in building a comprehensive climate observing system.
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This challenge is multifaceted. First, the major systems developed for operational weather forecasting rarely have the continuity and consistency required for climate research.
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and observationsuch as accurate, timely, and regular reporting on the techniques and algorithms used to collect and process data; knowing the differences in observing biases between new and old observing methods prior to eliminating the old observing method; and more effective use of existing data bases would make a critical difference to climate research. The collection of U.S.
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Satellite measurements must address and minimize the biases associated with drifting orbits that alias the diurnal cycle. New satellites and sensors must overlap the measurements of existing satellites prior to the decommissioning or decay of the latter in order to eliminate inhomogeneities in the climate record (Figure II.5.15~.
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Full and open exchange of data is an important element of the challenge to a climate observing system. We must take full advantage of existing observing systems by ensuring that operational observations can be utilized for climate research.
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We must collect a global climate data base of key variables and forcings sufficient to allow a statistical classification of natural variability and the identification of its predictable modes. These observations are also required both to determine how anthropogenic changes to the environment are altering or influencing natural climate variability and its predictable modes and to improve model predictions.
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In some areas, technological developments are required to make the needed climate observations practical outside the research mode. The development of a climate observing system, by taking full advantage of current observations and adding the key variables required to describe the climate system (e.g., water vapor)
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The continued collection and analysis of these paleoclimatic data are crucial, both for understanding the past history of the Earth's climate and for providing information needed to determine the ability of general circulation models to simulate large-scale climate change. To achieve as broad a representation of natural variability as possible, a substantial global data base has to be developed for each data type and for a variety of physical variables.
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Objective 4 Understand the major processes that govern climate variability through analysis of the observed record, correlation with natural and human forcing factors, focused process studies, and construction and analysis of coupled models of the climate system. The enhanced climate observing program (Objective 2)
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In such instances, considerable efforts should be made to improve the parameterizations of unresolved pro cesses. The development of coupled climate models is integral to understanding the processes that govern climate variability.
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A second paradigm focuses on the prediction of SST variations in the tropical Pacific and rainfall associated with these variations. This second case involves initializing the upper ocean with in situ measurements taken from the TOGA observing system, assimilating these observations into an ocean model to obtain the initial ocean conditions for the prediction, and then coupling the ocean to an initialized atmosphere and allowing the coupled system to evolve to a later prediction time.
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A well-defined record of decade-to-century variability derived from historical and paleoclimatic records and the identification, through exploration with coupled climate models and analysis of observations, of the fields and geographical distributions where decade-to-century variations may have predictability, will be a significant advance in our understanding of climate variability. The following requirements are essential to achieve this objective: 1.
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Improved knowledge of the fully coupled climate system can lead to an enhanced predictive capability that could support societal efforts to adjust to, forestall, or even eliminate some of the negative impacts of projected climate change. This enhanced ability to predict future climate will have a positive impact on economic vitality and national security.
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Fifth, model-data comparison is critical to diagnose and improve climate model predictions. In many cases, the suite of satellite and in situ data sets has been underutilized in efforts to validate climate models.
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2. Focus on key opportunities for reducing major uncertainties in climate models, including improved observations of water vapor and greater understanding of climate-water vapor feedbacks and improved representation of atmospheric chemistry and indirect chemistry-climate interactions.
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Develop and construct high-resolution, regional climate models along with empirical methods for producing estimates of climate change characteristics of immediate relevance to humans.
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However, a comprehensive climate research program that serves societal needs is clearly within our grasp. In many cases, programs required to achieve the objectives outlined in this report are in place.
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Requirements with Significant Budgetary or Programmatic Impact · Maintain major research observation systems, such as the TOGA TAO array, that have demonstrated clear predictive value. · Focus on key opportunities for reducing major uncertainties in climate models, including improved observations of water vapor.
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The addition of commitments for global aerosol measurement and solar energy input to the Earth system should be priorities. Extend the Instrumented Climate Record Through Development of Integrated Historical and Proxy Data Sets Requirements with Minimal Budgetary Impact · Widely sample the alpine glaciers and ice caps before this important repository of information on natural variability is lost.
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Third, we must recognize that these efforts are strong candidates for added support. Construct and Evaluate Models That Are Increasingly Comprehensive, Incorporating All Major Components of the Climate System Requirements with Minimal Budgetary Impact · Improve opportunities and enhance efforts at model observation and model-model comparisons that give particular attention to simulating observed changes associated with solar irradiance, aerosol loadings, and greenhouse gas concentrations.
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The observation and process study research described above are key to reducing major uncertainties in climate models and improving the representation of the atmosphere, ocean, biosphere, and cryosphere interfaces. If these efforts move forward, the major requirement will be (1)
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Funding agencies must be able to provide opportunities for a broad range of projects involving single and multiple investigators. Third, some elements of climate research, in particular the development of increased predictive skill, are more efficiently accomplished with dedicated facilities.
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predictions of anthropogenic interdecadal changes in regional climate, in the context of natural variability; 8. documentation of the level of greenhouse gas-induced global warming and documentation of other climatically significant changes in the global environment; and 9.
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