by Antonio J. Busalacchi1 and Ghassem R. Asrar2
In the wake of World War II, owing to advances in our observing and understanding of the dynamics of the atmospheric circulation, together with nascent digital computing and telecommunication technologies, the new field of numerical weather prediction was ushered in. The societal benefit of these scientific discoveries and technological innovations is manifest in present- day routine daily and weekly weather predictions.
Today, as a result of advances in climate science during the past 30 years, we are now seeing major advances in our ability to predict seasonal-to-interannual variability in Earth’s climate and project climate change on centennial timescales for major regions of the world. Looking to the future, we find ourselves at the beginning of a new era of predicting Earth System behaviour with tremendous potential to serve global society’s need for climate and environmental information from days to seasons, years to decades and longer. Coordination and collaboration among the nations around the world have been and will continue to be a hallmark of such progress.
The World Climate Research Programme (WCRP) was established in 1980 under the joint sponsorship of WMO and the International Council for Science (ICSU) and, since 1993, the Intergovernmental Oceanographic Commission (IOC) of UNESCO. The main objectives for WCRP since its inception are, to determine the predictability of climate and to determine the effect of human activities on climate. These fundamental objectives have laid the groundwork for present society’s adaptation and mitigation response strategies to changes in climate. Thanks to WCRP efforts, it is now possible for climate scientists to monitor, simulate and project global climate so that climate information can be used for governance, in decision-making and in support of a wide range of practical applications.
Over these 30 years, new disciplines of climate science have arisen that transcend traditional fields of atmosphere, ocean and land sciences and have led to routine seasonal-to-interannual climate predictions and longer-term climate projections. In parallel with such studies of natural fluctuations of the coupled climate system, the WCRP development of coupled climate models, driven by changes in the radiative forcing of greenhouse-gas emissions, has provided the climate change projections that have underpinned the assessments of the Intergovernmental Panel on Climate Change (IPCC) and the United Nations programme on assessment of atmospheric ozone depletion/recovery.
Modern climate science began with the creation of physically based numerical models of atmospheric and oceanic circulations in the 1950s and 1960s. In the 1960s and 1970s, observations from new Earth-orbiting satellites, ostensibly in support of weather prediction, began providing an unprecedented perspective of the Earth as an interconnected system of atmosphere, oceans, continents and life and temporal changes in this system much longer than that of day-to-day weather phenomena.
This first global perspective of the Earth’s atmospheric circulation and climate system enabled global climate studies and identified the important physical climate system processes. The idea of an international research programme on climate change came into being at Eighth World Meteorological Congress in May 1979, which formally established WCRP, inclusive of a climate research component (to be jointly managed by WMO and ICSU), as well as activities in gathering, managing and applying climate data and assessment of the potential impacts of climate change (to be managed by the United Nations Environment Programme (UNEP)). WCRP from the outset had two major foci: climate predictability and human influence.
WCRP identified the scientific complexity and breadth of the climate system: the Scientific Plan for the programme, prepared in 1984, recognized clearly the role of radiation, cloudiness, the ocean, the hydrological cycle and the biosphere. Oceans, land surfaces, the cryosphere and biosphere all needed to be represented realistically in global climate models. The extensive model development and numerical experimentation required the exploration of the sensitivity of the climate to changes in atmospheric carbon dioxide concentration (as well as other gases and aerosols). Early work on the assessment of research into carbon dioxide effects on climate anticipated IPCC needs. In view of the critical role of oceans in the climate system, close cooperation was established with the oceanographic community, with IOC joining as co-sponsor of the WCRP in 1993.
The first WCRP coupled atmosphere-ocean initiative, the Tropical Ocean and Global Atmosphere (TOGA) project, began in 1984. TOGA studied the influence of the slowly varying thermal inertia of tropical oceans on the large-scale atmospheric circulation. Recognition of the longer timescale or memory inherent to the oceans enabled short-term climate forecasts beyond the lead time of daily weather prediction. The requirement for ocean observations to initialize coupled forecasts established the prototype of the ocean observing system now in place.
During the TOGA decade, routine observations of the air-sea interface and upper-ocean thermal structure in the tropical Pacific Ocean were provided in real-time by the Tropical Atmosphere Ocean (TAO) array. These mooring observations have since been sustained in the Pacific and extended to the Atlantic and Indian Oceans, thus building a solid foundation for today’s ocean observing system.
Ocean data assimilation proved to be a key element to the initialization of seasonal-to-interannual climate forecasts. Coupled ocean-atmosphere prediction models were implemented at many of the world’s major weather prediction centres (Figure 1). This led to key breakthroughs in seasonal climate forecasts based on observations, understanding and modelling of worldwide anomalies in the global atmospheric circulation, temperature and precipitation patterns linked via teleconnections to El Niño. This was the beginning of the concept of climate products and services.
Figure 1 — Demonstration of successful ENSO forecasts such as displayed here for the 1997/1998 event have been possible through intensive research efforts in the field of seasonal prediction. The physical basis for understanding and predicting El Niño temperature signals and associated changes in the global atmospheric circulation from a season to a year in advance was laid during the WCRP project on Tropical Ocean and Global Atmosphere (TOGA, 1985-1994).
In addition, the overall approach to climate science evolved during TOGA. Prior to TOGA, in the early to mid-1980s, oceanographers and meteorologists were often in separate and distinct communities. As part of TOGA, these communities came together to form a new discipline of climate science realizing that there are modes of variability that occur in the coupled ocean-atmosphere system that do not exist in the uncoupled ocean or atmosphere.
Just as TOGA left behind a legacy upon which the subsequent Climate Variability and Predictability (CLIVAR) programme was established, so too did the WCRP World Ocean Circulation Experiment (WOCE) establish a solid foundation to study the ocean’s role in climate. WOCE was the largest and most successful global ocean research programme ever undertaken. Between 1990 and 1997, WOCE collected oceanographic data of unprecedented quality and coverage. These data, contributed by more than 30 nations, were fundamental in the development of basin-scale ocean models and have shaped our current understanding of mixing processes for energy and nutrients in the oceans. WOCE left a significant imprint on our knowledge of the global oceans, changes in the technology used by oceanographers and overall changes to the scientific methods for ocean research. During WOCE, a global perspective for the time-varying nature of the world’s oceans, from top to bottom, was realized.
The notion of a steady general ocean circulation or “snapshot” approach to observing the ocean was refuted by the repeat sections of the WOCE global hydrographic survey. This survey established a baseline to assess changes in time and evaluate anthropogenic effects on the global ocean circulation. In partnership with the US Joint Global Ocean Flux Study, a carbon dioxide and trace chemistry survey was enabled. Regional process studies and focused observational campaigns improved our knowledge of the Southern Ocean, deepwater formation in the Greenland-Iceland-Norwegian and Labrador Seas, and refinements to our understanding of the global thermohaline circulation and the meridional transport of heat from Equator to pole.
Advances in ocean technology played a major role in permitting a global ocean perspective. Continuous observations of global sea-surface height were provided by the TOPEX/Poseidon and European remote-sensing satellite radar altimeters. Active and passive microwave satellite sensors provided all-weather retrievals of the ocean surface wind velocity. Improved instrumentation and calibration led to refinements in air-sea flux measurement capabilities from both ship-and mooring-based platforms. Within the ocean, the WOCE float programme led to the ARGO programme and the concept of a global deployment of profiling floats. Experimental devices such as gliders demonstrated the potential for performing repeat sections in historically difficult-to-observe regions of the ocean such as western boundary currents.
Initiated by the WOCE Community Modelling Effort and fuelled by advances in computer technology, global ocean models now exist which can resolve energetic boundary currents and associated instability processes and provide a dynamically consistent description of many observed aspects of the ocean circulation that contribute to understanding the role of oceans in the Earth’s climate system. WOCE also changed the way the scientific community studies the ocean’s role in climate. The idea of an ocean synthesis in which in situ observations and/or remotely sensed observations are brought together with data-assimilation methodologies revolutionized the approach to global oceanography. Real-time global ocean observations have ushered in the possibility of operational oceanography on a global scale; an important theme of the upcoming Ocean Observations ’09 Conference (Venice, Italy, September 2009). We are now at the point that the oceanographic equivalent of a World Weather Watch is not a folly limited by logistics, but is in fact on the verge of reality.
Other important initiatives of WCRP were the International Satellite Cloud Climatology Project in 1982, the compilation of a Surface Radiation Budget dataset from 1985, and the Global Precipitation Climatology Project in 1985. These were based on exciting new techniques, developed to blend optimally remotely-sensed and in situ observations, providing for the first time new insights into the role of clouds in the climate system and the interaction of clouds with both radiation and the hydrological cycle. These activities formed the starting point for the comprehensive Global Energy and Water Cycle EXperiment (GEWEX) established in 1988, which is still one of the largest worldwide energy and water cycle experiments. As such, GEWEX leads the WCRP studies of the dynamics and thermodynamics of the atmosphere, the atmosphere’s interactions with the Earth’s surface (especially over land) and the global water cycle. The goal of GEWEX is to reproduce and predict by means of observations and suitable models the variations of the global hydrological regime, its impact on atmospheric and surface dynamics, and variations in regional hydrological processes and water resources and their response to changes in the environment, such as the increase in greenhouse gases.
GEWEX strives to provide an order-of-magnitude improvement in the ability to model global precipitation and evaporation, as well as accurately assess the feedback between atmospheric radiation, clouds, land use and climate change. To date, GEWEX has developed high-resolution, next-generation hydrologic land surface and regional climate models by improving parameterizations and applying them for experimental predictions. GEWEX has developed global datasets on clouds, radiation, precipitation and other parameters that are invaluable in understanding and predicting global energy and water cycles processes, and for their proper representation in the climate system models (Figure 2). Modelling studies and coordinated field experiments have identified key land-surface processes and conditions that contribute most significantly to the predictability of precipitation. GEWEX is developing land-data assimilation systems that will resolve land-surface features at resolutions as small as 1 km that will prove invaluable in studies and assessments of regional climate variability and change.
Figure 2 — Satellite-gauge combined precipitation product of the GEWEX Global Precipitation Climatology Project averaged for the 30 years 1979-2008, in mm per day. Data courtesy of GEWEX/GPCP; image by David Bolvin (SSAI), 5 June 2009, NASA/Goddard Space Flight Center, Greenbelt, MD.
Climate Variability and Predictability (CLIVAR), founded in the year 1995, is the main focus in WCRP for studies of climate variability. Monsoons, El Niño/Southern Oscillation and other global coupled atmosphere-ocean phenomena are investigated by CLIVAR on seasonal, interannual, decadal and centennial timescales. CLIVAR builds on—and is advancing—the findings of WCRP’s successfully completed TOGA and WOCE projects. CLIVAR further examines the detection and attribution of anthropogenic climate change based on high-quality climatic records.
Its mission is to observe, simulate and predict the Earth’s climate system, with a focus on ocean-atmosphere interactions enabling better understanding of climate variability, predictability and change for the benefit of society and the environment in which we live. CLIVAR seeks to encourage analysis of observations of climate variations and change on seasonal-to-centennial and longer timescales. It collaborates closely with GEWEX in studying and ultimately predicting the monsoon systems worldwide. It also encourages and helps to coordinate observational studies of climate processes, particularly for the ocean, but also over the monsoon land areas, encouraging their feed through into improvements in models.
CLIVAR promotes the development of a sustained ocean observing system both regional and globally. In collaboration with other WCRP projects, it is attempting particularly to understand and predict the coupled behaviour of the rapidly changing atmosphere and more slowly varying land surface, oceans and ice masses as they respond to natural processes, human influences and changes in the Earth’s chemistry and biota, while refining the estimates of anthropogenic climate change and our understanding of climate variability.
CLIVAR provides scientific input to the WCRP crosscutting topics on seasonal and decadal prediction and (with GEWEX) on monsoons and climate extremes. It also contributes to those on anthropogenic climate change and atmospheric chemistry (with Stratospheric Processes and their Role in Climate (SPARC)) and sea-level variability and change (with the Climate and Cryosphere (CliC) project, and cross-cutting scientific climate themes. CLIVAR achievements include the development of improved understanding and prediction of climate variability and change.
CLIVAR has provided coordination of climate model scenario experiments for IPCC, as well as key inputs on changes in climate extremes to the IPCC Fourth Assessment Report. Model intercomparison activities aimed at improving seasonal predictions and ocean model performance have been led by CLIVAR. Study of the ocean’s role in climate has been a major focus for coordination of field studies to help improve parameterization schemes for atmosphere and ocean climate models, synthesis of ocean data and advocacy for real-time ocean observations and high-quality delayed mode observations for ocean operations and research.
CLIVAR has organized major training workshops on seasonal prediction in Africa, climate impacts on ocean ecosystems, climate data and extremes and El Niño/Southern Oscillation. One specific example is the development of an electronic African Climate Atlas, as a tool for research on African climate.
Since 1993, the role of the stratosphere in the Earth’s climate system has been the focus of the WCRP project on SPARC. SPARC concentrates on the interaction of the atmosphere’s dynamical, radiative and chemical processes. Activities organized by SPARC include the construction of a stratospheric reference climatology and the improvement of understanding of trends in temperature, ozone and water vapour in the stratosphere. Gravity-wave processes, their role in stratospheric dynamics and how these may be parameterized in models are other current topics.
Research on stratospheric-tropospheric interactions have led to new understanding of tropospheric temperature changes initiated from the stratosphere. SPARC has organized model simulations and analyses that were a central element of the WMO/UNEP Scientific Assessments of Ozone Depletion and now recovery (Figure 3). SPARC-affiliated scientists have served on the WMO/UNEP Assessment Steering Committee, as lead and contributing authors and reviewers. In addition, SPARC comprehensive peer-reviewed reports include: “Trends in the vertical distribution of ozone”; “Upper tropospheric and stratospheric water vapour”; “Intercomparison of middle atmosphere climatologies”; and “Stratospheric aerosol properties”. WCRP researchers have also provided much of the scientific basis for the ozone protocols and carbon-dioxide- and aerosol-emission scenarios used by the United Nations Framework Convention on Climate Change (UNFCCC).
|Figure 3 — Through its project on Stratospheric Processes and their Role in Climate (SPARC), WCRP-related scientists have served on the WMO/UNEP Scientific Assessment Panel for Ozone Depletion as lead and contributing authors and reviewers. The schematic diagram shows the temporal evolution of observed and expected global ozone amounts. Image source: WMO/UNEP Scientific Assessment of Ozone Depletion 2006|
In 1993, the Arctic Climate System Study (ACSYS) opened up a polar perspective with the examination of key processes in the Arctic that have an important role in global climate. The scope of this study was broadened to the whole of the global cryosphere with the establishment of the Climate and Cryosphere (CliC) project in 2000. CliC was established to stimulate, support and coordinate research into the processes by which the cryosphere interacts with the rest of the climate system. The cryosphere consists of the frozen portions of the globe and includes ice sheets, glaciers, ice caps, icebergs, sea ice, snow cover and snowfall, permafrost and seasonally frozen ground, as well as lake-and river-ice. As a sensitive component of the climate system, the cryosphere provides key indicators of climate change (e.g. sea level rise, Figure 4), and CliC focuses on identifying patterns and rates of change in cryospheric parameters. CliC encompasses four themes, covering the following areas of climate and cryosphere science: The terrestrial cryosphere and hydrometeorology of cold regions; Ice masses and sea level; The marine cryosphere and climate; and Global prediction of the cryosphere.
Figure 4 — The climate knowledge and understanding we gain from research has to be made available to decision-makers in an open and timely manner in order to become beneficial to human society and the environment. For example, vulnerability assessments of coastal settlements and low-lying areas such as Pacific Islands and other island States prone to a rising sea level are based on the reconstructed and projected sea-level rise for the 21st century (m). A new WCRP activity within the Climate and Cryosphere (CliC) project now focuses on assessing the contribution of ice caps and glaciers on global sea level. Image source: modified and updated by J. Church, based on Church et al. 2001 in IPCC Fourth Assessment Report.
CliC generated strong input from the climate research community to the scientific programme of the International Polar Year 2007-2008. This included the concept of a polar satellite snapshot aimed at obtaining unprecedented coverage of both polar regions. CliC was one of the key scientific programmes that drew the attention of the world’s scientific community to the cryosphere. For the first time, a chapter on snow, ice and frozen ground was prepared in the IPCC Fourth Assessment Report. As detailed there, the contribution of melted water to recent sea-level change is now known with considerably increased accuracy.
The development and evaluation of global climate models is an important unifying component of WCRP, building on scientific and technical advances in the more discipline-oriented activities. These models are the fundamental tool for understanding and predicting natural climate variations and providing reliable predictions of natural and anthropogenic climate change. Models also provide an essential means of exploiting and synthesizing, in a synergistic manner, all relevant atmospheric, oceanographic, cryospheric and land-surface data collected in WCRP and other programmes. The Working Group on Numerical Experimentation (WGNE), jointly sponsored by WCRP and the WMO Commission for Atmospheric Sciences (CAS), leads the development of atmospheric models for both climate studies and numerical weather prediction.
The WCRP modelling programme has provided essential input to the four published assessments of the IPCC and is once again providing input to the next round of IPCC assessments. The WCRP Working Group on Coupled Modelling (WGCM) leads the development of coupled ocean/atmosphere/land models used for climate studies on longer timescales. WGCM is also WCRP’s link to the International Geosphere-Biosphere Programme’s (IGBP) Analysis, Integration and Modelling of the Earth System and to the IPCC. Activities in this area concentrate on the identification of errors in model climate simulations and exploring the means for their reduction by organizing coordinated model experiments under standard conditions. Under the purview of WCRP, the Atmospheric Model Intercomparison Project has facilitated controlled simulations by 30 different atmospheric models under specified conditions. The comparison of the results with observations has shown the capability of many models to represent adequately mean seasonal states and large-scale interannual variability.
Moreover, WGCM has initiated a series of Coupled Model Intercomparison Projects (CMIP). In 2005, WCRP facilitated the collection, archival and access to all the global climate model simulations undertaken for the IPCC Fourth Assessment Report. This third phase of CMIP (CMIP3) involved an unprecedented set of 20th-and 21st-century coordinated climate change experiments from 16 groups in 11 countries with 23 global coupled climate models. About 31 terabytes of model data were collected at the Program for Climate Model Diagnosis and Intercomparison. The model data are freely available and have been accessed by more than 1 200 scientists who have produced over 200 peer-reviewed papers, to date.
The first WCRP Seasonal Prediction Workshop was held in June 2007 in Barcelona, Spain, bringing together climate researchers, forecast providers and application experts to address the current status of seasonal forecasting and the application of seasonal forecasts by decision-makers. Workshop participants outlined recommendations and identified best practices in the science of seasonal prediction. During the workshop, the WCRP Climate-system Historical Forecast Project was launched. That project is a multi-model, multi-institutional experimental framework for assessing state-of-the-science seasonal forecast systems and for evaluating the potential for untapped predictability due to interactions of components of the climate system that are currently not fully accounted for in seasonal forecasts.
The World Modelling Summit for Climate Prediction, jointly sponsored by WCRP, IGBP and the WMO World Weather Research Programme (6-9 May 2008, Reading, United Kingdom) was organized to develop a strategy to revolutionize prediction of the climate through the 21st century to help address the threat of climate change. A key outcome of the Summit was the indisputable identification that our ability as a research community to make the transition from studies of global climate variability and change to application at the regional level has tremendous ramifications for present and future climate models, observations and needed infrastructure, such as high-performance computing.
Throughout its history, WCRP has had extensive interactions with many groups concerned with climate and climate research and has collaborated widely with other international scientific organizations on aspects of climate research that involve biogeochemistry, as well as physics. Multiple examples of active collaboration between WCRP and IGBP can be found in the GEWEX, SPARC and CLIVAR projects. Furthermore, WCRP strongly supported WMO’s establishment of the Global Climate Observing System (GCOS) in 1992 in cooperation with ICSU, UNEP and IOC. WCRP is also a co-sponsor of the international global change SysTem for Analysis, Research and Training (START) that promotes environmental research capacities in developing countries. In 2001, projections of possible future climate change and of increasing variations in climate stimulated the establishment of the Earth System Science Partnership between WCRP, IGBP, the International Human Dimensions Programme and the international programme of biodiversity science, DIVERSITAS. This partnership is promoting a coordinated focus on important global issues of common concern, namely the carbon budget, food systems, water systems and human health and similar important themes to human activities that could be affected by possible future climate change and increasing climate variability.
Looking to the future, the WCRP Strategic Framework for 2005-2015 period aims to facilitate analysis and prediction of Earth system variability and change for use in an increasing range of practical applications of direct relevance, benefit and value to society. A key focus of this Strategic Framework is towards seamless prediction of weather, climate and, ultimately, the whole Earth system. There are many theoretical and practical reasons for this approach to be pursued by the weather and climate community in adopting a seamless or unified approach to environmental prediction.
Extension of climate prediction to more encompassing environmental prediction requires recognition that the climate system is inextricably linked to the Earth’s biogeochemistry and to human activities. For WCRP to achieve its goals of understanding and predicting climate variability and change and their effect on society at large, it must, and will, contribute to studies of the fully integrated Earth system.
Developing a unified approach to weather, climate, water and environmental prediction requires a broadened Earth system perspective beyond the traditional atmospheric science disciplines. The development of climate prediction and ultimately environmental prediction is not a rote extension of numerical weather prediction. For example, the scientific disciplines required to support weather, climate and environmental prediction across these timescales span meteorology, atmospheric chemistry, hydrology, oceanography and marine and terrestrial ecosystems.
While atmospheric nowcasting and very short-range weather forecasting are primarily initial value problems, extension to short-, medium-and extended-range weather forecasting begins to bring in the coupling of land-surface processes and the role of soil moisture feedback and other surface-atmosphere processes. Long-range forecasting through seasonal climate forecasting involves atmosphere-ocean coupling with the initial conditions of the memory inherent in the upper ocean leading to longer lead-time predictive skill.
Decadal climate prediction is determined by both initial values and boundary-value forcing. On these timescales, deeper oceanic information and changes to radiative forcing from greenhouse gases and aerosols play determinant roles. When considering interdecadal to centennial climate projections, not only do future concentrations of greenhouse gases need to be taken into account, but also changes in land cover/dynamic vegetation and carbon sequestration governed by both marine and terrestrial ecosystems. In addition, regionally specific predictive information will be required across these timescales for environmental parameters such as air and water quality.
|Figure 5 — Global average of annual-mean Earth surface temperature anomaly (1979-2001) forecast by the UK Met Office Decadal Prediction System (DePreSys) beginning in June 2005. The confidence interval (red shading) is diagnosed from the standard deviation of the DePreSys ensemble mean (white curve). The blue curve is an equivalent forecast with no initialization with observations. The black curve is the hindcasts beginning from June 1985 together with observations. Source: Smith et al. (2008, Science 317)|
One of WCRP’s major challenges is to determine the limits to predictability on the decadal timescale. Within the concept of a unified suite of forecasts, decadal prediction bridges the gap between predicting seasonal-to-interannual climate variability and change and the externally forced climate change projections over very long periods, i.e. a century. The climate-change community is typically focused on the problem of estimating anthropogenically induced climate change on centennial timescales. For this community, the provision of accurate initial conditions is not a major concern, since the level of predictability of the first kind is believed to be small on century timescales.
By contrast, although the numerical weather prediction and seasonal forecast community have well-developed data-assimilation schemes to determine initial conditions, the models do not incorporate many of the cryospheric and biogeochemical processes believed to be important on timescales of centuries. A focus on decadal prediction by the two groups may help expedite the development of data-assimilation schemes in Earth system models and the use of Earth system models for shorter-range prediction, e.g. seasonal. For example, seasonal predictions can be used to calibrate probabilistic climate-change projections in a seamless prediction system. Hence, there is common ground over which to base a cooperation of the two communities in order to develop seamless predictions.
Over the past 20 years, the link between WCRP observational and modelling efforts has been atmospheric reanalyses that have greatly improved our ability to analyse the past climate variability. The Third WCRP International Conference on Reanalysis was held in Tokyo from 28 January to 1 February 2008 to showcase results of progress in reanalysis products and research and to discuss future goals and developments. The climate record is made up of analyses of observations taken for many other purposes, such as weather forecasting in the atmosphere or core oceanographic research. It is now recognized that global climate can be understood only by ensuring that there are climate-quality observations taken in the atmosphere, ocean and land surface, including the cryosphere.
A consequence of past practices is that the climate record often displays biases that mask long-term variations. Many climate datasets are inhomogeneous: the record length is either too short to provide decadal-scale information or the record is inconsistent, owing to operational changes and absence of adequate metadata. Hence, major efforts have been required to homogenize the observed data for them to be useful for climate purposes. Reanalysis of atmospheric observations using a constant state-of-the-art assimilation model has helped enormously in making the historical record more homogeneous and useful for many studies. Indeed, in the 20 years since reanalysis was first proposed, there have been great advances in our ability to generate high-quality, temporally homogeneous estimates of past climate. WCRP and GCOS have provided leadership in promoting the underpinning research and observational needs for reanalysis. With the ongoing development of analysis and reanalysis in the ocean, land and sea ice domains, there is huge potential for further progress and improved knowledge of the past climate record.
From the Conference, it was apparent that much future work remains to be done to address outstanding issues in reanalyses, especially those related to the changing observational data base. These issues adversely affect decadal and longer variability and limit applications of reanalyses at present. Moreover, while the origins of reanalysis have been in atmospheric climate and weather, there have been significant studies of reanalysis (or synthesis) of ocean data. Because of the limited size of the historical ocean datasets, it has been necessary to develop novel techniques for increased homogeneity of ocean reanalysis. Other promising developments are occurring in sea ice, Arctic and land surface reanalysis. There has also been initial development of coupled atmosphere-ocean data assimilation, which is laying the foundation for future coupled reanalysis studies that may lead to more consistent representations of the energy and water cycles. A challenge is to improve estimates of uncertainty in the reanalysis products.
Figure 6 — A conceptual framework for a climate information system which begins with observations, research and analysis and results in information required by the decision-makers. The decisions on priorities and coordination among component of the system are informed by the need for scientific understanding together with the type of climate information required by the decision-makers. Source: Trenberth (2008), WMO Bulletin 57 (1), January 2008, slightly modified by G. Asrar
Global atmospheric reanalysis results in high-quality and consistent estimates of the short-term or synoptic-scale variations of the atmosphere, but variability on longer timescales (especially decadal) is not so well captured by current reanalyses. The primary causes of this deficiency are the quality and homogeneity of the fundamental datasets that make up the climate record and the quality of the data-assimilation systems used to produce reanalyses. Research into bias corrections and advanced reanalysis techniques is showing promise, however, and further reanalysis efforts are needed. In the future, it will prove important that next-generation global reanalyses are coordinated and, if possible, staggered to ensure that the basic observational data record is improved before each reanalysis, so that there is time to analyse and hence learn from the output of past efforts. Further improvements to reanalyses, including expansion to encompass key trace constituents and the ocean, land and sea-ice domains, hold promise for extending their use in climate-change studies, research and applications.
Another challenge confronting the climate research community is the provision of climate information on the regional level that investors, business leaders, natural resources managers and policy-makers need to help prepare for the adverse impacts of potential climate change on industries, communities, ecosystems and entire nations (Figure 6). While global mean metrics of temperature, precipitation and sea-level rise are convenient for tracking global climate change, many sectors of society require actionable information on considerably finer spatial scales. The increased confidence in attribution of global-scale climate change to human-induced greenhouse-gas emissions, and the expectation that such changes will increase in future, has lead to an increased demand in predictions of regional climate change to guide adaptation. Although there is some confidence in the large-scale patterns of changes in some parameters, the skill in regional prediction is much more limited and indeed difficult to assess, given that we do not have data for a selection of different climates against which to test models.
Much research is being done to improve model predictions but progress is likely to be slow. In the meantime, WCRP recognizes that governments and businesses are faced with making decisions now and require the best available climate advice today. Despite their limitations, climate models provide the most promising means of providing information on climate change and WCRP has encouraged making data available from climate predictions to guide decisions, provided the limitations of such predictions are made clear. This will include assessments of the ability of the models used to predict current climate, and the range of predictions from as large a number of different models as possible.
Toward this end, WCRP has begun to develop a framework to evaluate regional climate downscaling (RCD) techniques for use in downscaling global climate projections (Giorgi et al., 2009). Such a framework would be conceptually similar to the successful coupled model intercomparisons undertaken by WGCM and would have the goal of quantifying the performance of regional climate modelling techniques and assessing their relative merits. An international coordinated effort is envisioned to develop improved downscaling techniques and to provide feedback to the global climate modelling community. A specific objective will be to produce improved multi-model RCD-based high-resolution climate information over regions worldwide for input to impact/adaptation work and to the IPCC Fifth Assessment Report (AR5). This would promote greater interactions between climate modellers, those producing downscaled information and end-users to better support impact/adaptation activities and to better communicate the scientific uncertainty inherent in climate projections and climate information. An important theme in this activity will be the greater involvement of scientists from developing countries.
Over the next few years, WCRP will continue to provide the scientific leadership for major international climate assessment activities. Currently, under the leadership of WCRP’s WGCM, the fifth phase of CMIP (CMIP5) is under development in support of IPCC AR5. The grand challenge of the new set of climate models examined in CMIP5 is to resolve regional climate changes, particularly in the next few decades, to which human societies will have to adapt, and to quantify the magnitudes of the feedbacks in the climate system, such as in the carbon cycle.
The scientific community has formulated the proposed CMIP5 coordinated experiments to address key science questions. Since these experiments will be the major activity of the international climate change modelling community over the next few years, the results will be eligible for assessment by AR5. The new suite of coupled model experiments is based on the use of two classes of model to address two time frames and two sets of science questions. For longer timescale projections (to 2100 and beyond) (Figure 7), and as an extension to previous WGCM modelling supporting IPCC, intermediate resolution (~200 km) coupled climate models will incorporate the carbon cycle, specified/simple chemistry and aerosols, forced by new mitigation scenarios (referred to as “representative concentration pathways”. The science questions to be addressed relate to the magnitude of feedbacks in the coupled climate system. Mitigation and adaptation scenarios with permissible emissions levels that allow the system to hit stabilized concentration targets are to be used (in place of the previous IPCC Special Report on Emissions Scenarios). The new scenarios will have implicit policy actions to target future levels of climate change. Since we can only mitigate part of the problem and we will have to adapt to the remaining climate change, the challenge is to use climate models to quantify time-evolving regional climate changes to which human societies will have to adapt.
|Figure 7 — Regional anomalies maps published in South America chapter from BAMS State of the Climate 2005|
A new focus area for CMIP5 is a set of near-term projections that encompass 10-and 30-year prediction studies and high-resolution time-slice experiments, as summarized in Taylor et al., 2008. WCRP research has indicated there are reasonable prospects for producing decadal forecasts of sufficient skill to be used by planners and decision-makers, as well as being of considerable scientific interest. The CMIP5 experimental design provides an opportunity for the international coordination of research and experimentation in this area.
There are two aspects to the decadal problem; the externally forced signal (greenhouse gases and aerosols, volcanoes, solar, etc.) and the predictable part of the internally generated signal from intrinsic oceanic mechanisms, coupled ocean-atmosphere processes, modulation of climate modes of variability (e.g. El Niño/Southern Oscillation) and, potentially, land and cryospheric processes. To date, climate projections have generally treated internal variability as a statistical component of uncertainty. Though there is no marked decadal peak in the spectrum of the climate system, long timescales exist and are potentially predictable. The challenge of prediction/predictability studies is to identify the mechanisms associated with regions/modes of predictability, to better understand the connection between oceanic modes and terrestrial climate variability and to investigate predictive skill by means of prognostic (including multi-model) decadal predictions.
The results of predictability studies and demonstrations of forecast skill provide the foundations for initiating a coordinated WCRP study of decadal prediction/predictability. There are abundant scientific opportunities to improve and extend models and for the analysis of variability and of modes of variability. Future challenges include the need to develop improved analysis methods, especially in the ocean, and for model initialization, verification and development, as well as in ensemble generation and the use of multi-model ensembles for prediction on decadal timescales.
In addition to its support of the IPCC assessment process, WCRP will continue to support the quadrennial WMO/UNEP Ozone Assessment. The SPARC Chemistry Climate Model Validation Activity (CCMVal) is the main model-based analysis for the connection between atmospheric chemistry and climate. CCMVal provides strategic modelling support to the ozone assessment process that is mandated by the Montreal Protocol. Ozone is a major constituent in radiative processes and is also affected by dynamics and transport. Only CCMs can simulate the feedback of chemical processes on the dynamics and transport of trace gases.
Under the direction of WCRP SPARC, CCM simulations will be conducted as a major contribution to the WMO/UNEP Scientific Assessment of Ozone Depletion: 2010. The main focus will lie on model validation against observations, as well as on assessments of the future development of stratospheric ozone. At present, ozone recovery is expected to take place until mid-century (WMO, 2007; Eyring et al., 2007), when column ozone is expected to reach 1980 values in southern polar latitudes. This development is determined on the one hand by a decrease in ozone depleting substances and on the other hand by a decrease in stratospheric temperatures due to enhanced greenhouse-gas concentrations in the atmosphere, which affects polar stratospheric cloud formation and heterogeneous ozone destruction.
An important issue is how the changes in the tropospheric abundances of ozone depleting substances translate to changes in the ozone-depleting active chemicals in the stratosphere. Dynamical processes that control transport and dynamical issues related to vortex formation and maintenance need to be carefully taken into consideration when predicting the long-term evolution of polar ozone. The influences of the changes in stratospheric ozone and composition on the Earth’s climate that need to be evaluated include those that can influence the composition of the troposphere. For studies of the future development of stratospheric ozone, it is of great importance to take into account the interactions of radiation, dynamics and chemical composition of the atmosphere.
In summary, WCRP has made great strides in advancing understanding of the coupled climate system on timescales ranging from seasonal to centennial. WCRP research efforts resulted in the reality of operational climate forecasting, products and services. WCRP has had a major role in transferring the resultant scientific information and knowledge about the Earth’s climate system for policy decisions through the IPCC, the UNFCCC Conference of Parties and its Subsidiary Body on Scientific and Technological Advice. More than one half of the scientific and technical contributions used in the IPCC assessments were provided by WCRP-affiliated scientists. WCRP made a concerted effort to provide worldwide access to its model predictions/projections and research results for use by scientists from developing and Least Developed Countries to assess the consequences of potential climate variability and change on major economic sectors (e.g. food, water, energy, health), for their country or geographic region.
WCRP’s accomplishments and progress were all made possible by the generous and sustained contributions of its sponsors: WMO, ICSU and IOC, and their network of more than 190 Member countries. The entire WCRP community is grateful for this sponsorship and support and is excited about the many opportunities that have made possible major contributions to understanding the causes and consequences of climate change and variability, assessing their impact on major sectors of the world economy and enabling the use of resulting knowledge for managing the risks associated with these changes for our generation, our children and those who will follow them in this century and beyond.
WCRP work has established, unequivocally, that the Earth System will experience real climate change over the next 50 years, exceeding the scope of natural climate variability. A question of paramount importance confronting nations is how to adapt to this certainty of climate variability and change in the next half century. The needs for coping with climate variability and adapting to climate change therefore represent a real challenge to society. In response, the upcoming World Climate Conference-3 will consider how comprehensive climate services would best inform decisions about adaptation.
The delivery of climate observations and services involves the transition across basic research, applied research, operations, applications and engagement with the user community. Yet, most of the effort to date has been focused on the physical climate system and has not been product-driven. However, climate impacts and services involve sectors such as business, finance, agriculture, engineering, public health, public policy, national security, etc. In order to satisfy the needs of society for climate services, a climate information system is called for by decision-makers to support policy, budget and investment decisions. Such a system would build upon reliable climate predictions over timescales of seasons to decades, tailored forecasts for regions and localities, integration of atmospheric, oceanic, terrestrial and social data into a comprehensive “Earth System” prediction model and decision-support interfaces that can be adjusted to provide user-specified “if-then” scenarios.
The realization of a climate information system will require the coupling of models across the physical climate system, biogeochemical cycles and socio-economic systems, synthesis of disparate datasets from in situ and space-based observations, new terrestrial and orbital sensor systems, dedicated high-performance computer infrastructure and software and unprecedented synergy between the climate research community, the operational delivery arm of climate services, and the end users. Much akin to the situation 60 years ago with the advent of numerical weather prediction, we now find ourselves on the brink of a new era of climate information and services underpinned by climate research striving to improve, expand and refine our understanding and ability to predict the coupled climate system.
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1 Director, Earth System Science Interdisciplinary Center, University of Maryland, College Park, USA
2 Director, World Climate Research Programme, WMO