All human and natural systems are affected by climate. For the most part, these systems have successfully adapted to the present climate and to its natural variability. For example, the annual cycle of the seasons represent "climate changes" far greater than the changes in average conditions currently projected due to human activities. However, these seasonal changes occur in a regular and highly predictable manner and so are variations to which humans and natural systems have readily adapted. But, there are more subtle variations and changes in Earth's climate that are considerably more challenging to predict, and to which both human and natural systems may be much more vulnerable. Instrumental records and paleoclimate data provide compelling evidence of substantial variability and change in the Earth's climate on time scales from seasons to centuries, including extreme climate events such as extended droughts and abrupt changes in global and regional climates. Thus, the notion of an unchanging, or stationary, climate is untenable. We are only now learning what aspects of natural and human-induced climate variations and change are predictable in theory, and in practice, on time scales of seasons to centuries. Credible climate predictions provide scientific guidance that is essential to increasing societal resilience and the capacity to adapt to future variability and change.
For this reason and also because decadal climate variability, in particular, is such a fascinating and complex topic of study, we are delighted to have been asked by Dr Vikram Mehta to provide a short article on decadal variability for the inaugral issue of the web-based Virtual Center for Decadal Climate Variability.

The Fereral agencies that support the U.S. Global Change Research Program (USGCRP) are in the final stage of planning its research agenda for the current decade. Following approval based on government and public review, the results will be published as the USGCRP’s long-range strategic plan. The authors of this article are the co-chairs for the Climate Variability and Change component of the plan, which has been identified by the agencies as one of six science elements that will be the Program’s focus during this decade. The others are Atmospheric Composition, the Carbon Cycle, the Water Cycle, Terrestrial and Marine Ecosystems, and Land Use/Land Cover Change. Climate Variability and Change research will be formulated, coordinated and conducted under the international and USGCRP’s Climate Variability and Predictability Program (CLIVAR) and the World Meteorological Organization (WMO) World Climate Research Program’s (WCRP) Coupled Model Intercomparison Project (CMIP), and will be closely coordinated with the international Global Energy and Water Cycle Experiment (GEWEX), as well as all other components of the USGCRP and WMO.

The research will focus on two overarching questions:

1. How are climate variables, especially temperature, precipitation, clouds, winds, and storminess, affected by changes in the EarthÕs environment that result from natural and human activities?; and
2. How will climate variability and change affect the life-sustaining services that humans draw from the environment, and how can we best communicate this information to support public and private sector decisions that will improve risk management, reduce vulnerability, and enhance resilience?

To answer these questions we will require a vigorous and aggressive research agenda, in collaboration with international partners and centered around five goals.

Goal 1 - Improve detection, attribution, and projections of climate change.
Improving understanding about the causes of climate change and reducing uncertainty about current and projected future changes is essential to provide the sound scientific underpinning for climate impacts assessments and future policy decisions.

Goal 2 - Extend and improve predictions of major modes of climate variability.
Incorporating the growing understanding of mechanisms producing different patterns of climate variability, such as ENSO, the North Atlantic Oscillation (NAO), Arctic Oscillation (AO), and the Pacific Decadal Oscillation (PDO) into climate models provides the potential to extend and improve predictions of climate variations and their regional impacts. Continuing improvements in climate predictions will enable better planning and decision-making related to climate variability and change across a wide range of sectors, including water, energy, and agriculture

Goal 3 - Assess the potential for changes in extreme events at regional to local scales.
Societies and ecosystems are often most vulnerable, and least resilient, to the environmental stresses produced by extreme weather and climate events. The need for improved information on such events, particularly at regional to local scales, is one of the highest priorities for users of climate information. Major droughts, floods, heat waves, hurricanes, and storm surges are examples of extreme events that have major economic and social impacts, and whose frequencies, intensities, and geographical distributions may change in the future.

Goal 4 - Characterize the mechanisms and estimate the likelihood of abrupt climate change and its expected global and regional manifestations.
Abrupt climate change in the past has been evident as a result of significant shifts in the baseline climate and the character and pattern of its variations. Such changes may occur over periods of years to decades and be associated with the crossing of a climatic threshold, the onset of nonlinear responses, or other unusual phenomena for which society would be unlikely to be prepared given notions of gradual changes and historic experiences with climate variations. Abrupt climate change, whether on global or regional scales, poses among the largest potential threats to society and ecosystems. Paleoclimate data show that abrupt regional-to-global climate changes have occurred often in the past, and some models suggest the possibility for abrupt changes within this century. Improved information on the probabilities and risks of abrupt climate changes, as well as the potential for climate "surprises," will support development of informed environmental policies and adaptation strategies.

Goal 5 - Improve effectiveness of interactions between producers and users of climate forecast information.
The full potential value of climate information will be realized only when it can be provided in forms that are useful for addressing fundamental societal issues, such as public health and safety, agriculture, energy and water resource management, forest, range and wetland management, and sustainable economic development. Better understanding and identification of the critical needs of users and decision-makers by the research community will result in the production of more accessible, timely, and usable climate information. Achieving these goals will require new research infrastructure, including:

1. establishment of a highly focused and adequately funded modeling and prediction facility that will develop for multiple applications a suite of the most complex climate and Earth system models;
2. a high-level international commitment to a sustained, long-term observing system of a quality adequate for climate research and assessments; and
3. a standing infrastructure, drawing broadly from USGCRP and other research activities, that supports national and international climate change assessments on a regular and continuing basis.

And, most importantly, success in acheiving these goals will depend on the continued creative and productive research and dedication of climate scientists, including their mentoring of the students and post-docs who will plan and conduct our science in future decades.

We welcome the commencement of this newsletter and look forward to the interesting, informative and useful materials that it will provide.