Advances in our understanding of the climate system have been and will continue to be a critical underpinning for evaluating the risks and opportunities posed by climate change as well as evaluating and improving the effectiveness of different actions taken to respond. Hence, even as actions are taken to limit the magnitude of future climate change and adapt to its impacts, it is important that continued progress be made in observing all aspects of the climate system, in understanding climate system processes, and in projecting the future evolution of the climate system, and as well as its interactions with other environmental and human systems (which are explored in the chapters that follow). The following are some of the most critical basic research needs in these areas.
Expand and maintain comprehensive and sustained climate observations to provide real-time information about climate change. Regular and sustained observations of climate variables are needed to monitor the progress of climate change, inform climate-related decision making, and to monitor the effectiveness of actions taken to respond to climate change. Observations are also critical for developing and testing climate models, projections of future climate forcing, and other tools for understanding and projecting climate change, as well as for supporting decision-support activities. As discussed in Chapter 3, a comprehensive climate observing system is needed to provide regular monitoring of biological, chemical, geological, and physical properties in the atmosphere, oceans, land, and cryosphere, as well as related biological, ecological, and socioeconomic processes. Expanded historical and paleoclimatic records would also be valuable for understanding natural climate variations on all time scales and how these modes of variability interact with global climate change. Finally, a comprehensive data assimilation system is also needed to bring these disparate observations into a common framework, so that the state of the whole Earth system can be assessed and impending feedbacks that could alter the rate of climate change can be identified. Research is especially needed on how to better integrate physical indicators with emerging indicators of ecosystem health and human well-being, as discussed in other chapters.
Continue to improve understanding of climate variability and its relationship to climate change. Great strides have been made in improving our understanding of the natural variability in the climate system over the past several decades. These improvements have translated directly into advances in detecting and attributing human-induced climate change, simulating past and future climate in models, and understanding the links between the climate system and other environmental and human systems. For example, the ability to realistically simulate natural climate variations, such as the El Nino-Southern Oscillation, is a critical test for climate models. Improved understanding of regional variability modes is also critical for improving regional climate projections, as discussed below. Understanding the impacts associated with natural climate variations also provides insight into the possible impacts of human-induced climate change. Continued research on the mechanisms and manifestations of natural climate variability in the atmosphere and oceans on a wide range of space and time scales, including events in the distant past, can be expected to yield additional progress.
Develop more informative and comprehensive scenarios of drivers of future climate forcing and socioeconomic vulnerability and adaptive capacity. Uncertainty in projections of the future is inevitable. However, the development of scenarios allows better understanding of the dynamics of the interconnected human-environment system and in particular how the dynamics will change depending on the choices we make. Scenarios are also critical for helping decision makers establish targets for future GHG emissions and concentration levels as well as helping make plans to adapt to the future projected impacts of climate change, topics addressed in many of the chapters that follow. Developing and improving assessments of the potential influence of various policy choices on emission profiles and adaptive capacity is particularly important in the context of supporting climate-related decision making—especially "overshoot" scenarios, which have the potential to cause irreversible changes to the climate system. Influences of shorter-lived forcing agents (including short-lived GHGs and aerosols) are also of high importance in the near term and could benefit from more near-term emphasis.
Developing enhanced scenarios and linking them to a variety of Earth system and socioeconomic models is an inherently interdisciplinary and integrative activity requiring contributions from many different scientific fields as well as processes that link scientific analysis with decision making and, ideally, public deliberation about desirable futures. The new "Representative Concentration Pathways" described earlier represent a few common, transparent, thoroughly documented representative scenarios of key variables over time. A number of research needs and developments are required to develop new socioeconomic scenarios that explore both mitigation and adaptation issues. It is particularly important to explore methods for coupling scenarios across geographic scales (from global to regional to local), to further develop methods for downscaling climate scenarios and providing regional climate information, and to develop data and information systems for pairing socioeconomic and climate scenarios for use in impacts research and to support the needs of particular decision makers.
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