Climate Variability and Change

1. Chapter 6 Climate Variability and Change Draft Strategic Plan U.S. Climate Change Science Workshop December 04, 2002 1

2. CVC Working Group Lead Authors Contributors Randall Dole (Co-Chair), NOAA Anjuli Bamzai, NOAA Jay Fein (Co-Chair), NSF Steven Meacham, NSF David Bader, DOE Tony Socci, EPA Ming Ji, NOAA James Todd, NOAA Tsengdar Lee, NASA David Legler, CLIVAR Michael Pavich, USGS 2

3. Background Results from climate science research: • It is likely that the rate and duration of global warming during the 20th century exceeds natural variability of the past 1000 years. • Model simulations that include estimates of natural and anthropogenic forcing are able to reproduce large scale aspects of the observed surface warming over this past century.

4. Background (cont.) • Model projections based on a range of possible scenarios suggest that climate changes over this century will be larger than what has been observed up until now. • Due to natural processes, rapid climate changes can occur in decades or less, yet last for centuries or longer. • Major advances in observations, understanding, and modeling of El Niño Southern Oscillation (ENSO), which have given the world an unprecedented opportunity to prepare for and reduce vulnerabilities to this major natural climate phenomenon.

5. Some major challenges • Continuing uncertainties on climate system sensitivity to various feedbacks (e.g., clouds, water vapor, snow). • Several natural modes of climate variability have been identified and described, but their predictability is uncertain. • Need to improve understanding of whether and how human impacts may alter natural climate variability. • Do not yet have confident assessments of the likelihood of abrupt climate changes. • Insufficient understanding of effects of climate variability and change on extreme events. • Limited capabilities at regional scales. • Need better means for identifying, developing, and providing climate information required for policy and resource management decisions.

6. Key references • IPCC Third Assessment Report: The Scientific Basis (WG1, 2001). NRC Reports: • Climate Change Science: An Analysis of Some Key Questions (2001). • Global Environmental Change: Research Pathways for the Next Decade (1999). • U.S. Climate Modeling Reports (1998, 2001). • Abrupt Climate Change: Inevitable Surprises (2002) • The Atmospheric Sciences: Entering the Twenty-First Century (1998). • Making Climate Forecasts Matter (1999). • A Climate Services Vision (2001). • Other planning documents, e.g., CLIVAR Science Plan.

7. Overarching questions How are the climate elements that are important to human and natural systems, especially temperature, precipitation, cloudiness, and storminess, affected by variations and changes in the Earth system that result from natural processes and human activities? How can emerging scientific findings on climate variability and change be further developed and communicated to most effectively meet the needs of policymakers and public and private sector decisionmakers, in order to enhance human well-being, strengthen the economy, and reduce risks and vulnerability of climate sensitive activities and resources?

8. Major Questions 1. What is the sensitivity of climate change projections to feedbacks in the climate system? Q1 focuses on the fundamental issue of the role of climate feedbacks in producing uncertainties in climate change assessments and projections. To what extent can predictions of near-term climate fluctuations and projections of long-term climate change be improved, and what can be done to extend knowledge of the limits of predictability? Q2 focuses on theoretical and practical limits of predictability of the coupled climate system.

9. Questions (cont.) What is the likelihood of climate-induced changes that are significantly more abrupt than expected, such as the collapse of the thermohaline circulation or rapid melting of the major ice sheets? Whether and how are the frequencies, intensities, and locations of extreme events, such as major droughts, floods, wildfires, heat waves, and hurricanes, altered by natural climate variations and human-induced climate changes? Q’s 3 and 4 emphasize issues of high practical significance to societies and ecosystems -- abrupt climate change and extreme events.

10. Questions (cont.) How can interactions between producers and users of climate variability and change information be optimally structured to ensure essential information needed for formulating adaptive management strategies is identified and provided to decisionmakers and policymakers? Q5 emphasizes the need for improved mechanisms to identify and provide climate information that will better support the needs of the public, resource managers, and policymakers.

11. Some products • Refined estimates of the role of climate feedback processes in affecting climate sensitivity, and reductions in known uncertainties. • Development and extension of critical data sets, including paleoclimate data and model-based reanalyses, to improve attribution of causes of long-term climate variations. • A new estimate of sea level rise that incorporates the most recent ice sheet and glacier change estimates. • An assessment of how climate extremes are likely to change over the United States in the next century. • A geographical information system that includes data on current extreme events, and locations of vulnerable populations and infrastructure. • Improved climate information for regional applications and risk reduction.

12. Payoffs • More certain estimates of the global and regional manifestations of future climate changes. • Increased understanding and confidence in attributing the causes of recent and historical changes in climate. • Improved ability to critically evaluate the strengths and weaknesses of climate change projections. • Improved understanding of thresholds and nonlinearities in the climate system. • An enhanced capability to evaluate potential scenarios of change in both extreme events and vulnerabilities, to develop strategies for reducing disaster-related losses. • Improved access to climate information and products for addressing regional concerns and issues.

13. Critical Research Needs • A highly focused and adequately funded modeling and prediction activity. • A research-based infrastructure to develop and provide the scientific information required by decisionmakers and resource managers, and to support national and international climate assessments. • A high-level international commitment to a sustained, long-term observing system of a quality adequate for climate research and assessments.

14. Linkages • Primary USGCRP linkages are to the Water Cycle, Atmospheric Composition, and Carbon Cycle. Significant linkages to all other elements. • Strong linkages to CCRI components of Research Focused on Key Climate Change Uncertainties, Climate Quality Observations and Monitoring, and Decision Support Resources, especially applied climate modeling. • Other critical linkages are to internationally coordinated research programs, including the World Climate Research Programme (WCRP) and its projects, CLIVAR, GEWEX, SPARC, CliC, and the IGBP PAGES paleoscience project.