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Initiative Overview


Climate and Weather create hazards and opportunities for society at multiple scales. Assessment science seeks to improve the processes and methods for generating and communicating scientific knowledge to improve decision-making. The NCAR Climate and Weather Impact Assessment Science Initiative focuses on critical scientific gaps in the weather and climate arenas that have proved particularly challenging for decision-makers and scientists alike:

    1. characterizing uncertainty;
    2. extreme weather and climate events; and
    3. the role of climate in human health.

The Initiative addresses the following specific scientific objectives under these themes:

  • To quantify uncertainties in climate model simulations related to multiple forcings (i.e., greenhouse gases plus land cover change, and natural forcings--solar variability, aerosols from volcanic eruptions) in climate models;

  • To characterize uncertainty on regional scales in climate projections that support decision-making;

  • To determine new robust measures of changes in weather and climate extreme events and their uncertainties (using extreme value theory), for extremes relevant to societal impacts;

  • To nurture an interdisciplinary research community to address the interactions between climate and human health; and

  • To work towards end-to-end integrated projects in extreme events and uncertainty that encompass physical science, impacts, and decision-making.

Research in the NCAR Weather and Climate Impact Assessment Science Initiative is grouped into three main themes, plus one overarching integrating theme:


Theme 1: Characterizing Uncertainty

Characterizing UncertaintyA major function of the Intergovernmental Panel on Climate Change (IPCC) is to "assess the state of our understanding and to judge the confidence with which we can make projections of climate change and its impacts." As stated by Moss and Schneider (2000) understanding how to consistently assign probabilities to outcomes or processes that encompass various types of uncertainties is very difficult even in the research realm. Communicating uncertainty to decision-makers in a form that makes it useful for policy-making is yet another difficult challenge. Uncertainty itself has various meanings and levels—it can refer to lack of knowledge, lack of certainty, disagreement among experts, or the fundamental nature of the scientific process which experiences uncertainties as part and parcel of the experimental method.

There is therefore a strong need for studying aspects of the uncertainty of climate projections, in order for scientists to be explicit about where estimates of uncertainties come from. The projects grouped under this theme tackle some of the key uncertainties that have been identified by previous assessment processes. The major objectives of this theme include developing new techniques for quantifying uncertainty in climate model projections and applying these techniques to recent transient runs of atmosphere-ocean general circulation models (AOGCMs). Recent emphasis is given to quantifying regional uncertainty. In order for scientific information to inform decision-making, we must understand how decision-makers use information and make decisions under uncertainty. A critical project under development in the Initiative is creating an integrated assessment of uncertainty embracing the physical system impacts and decision-making.


Theme 2: Methods and Assessment of Extreme Weather and Climate Events

Methods and Assessment of Extreme Weather and Climate EventsLoss of life and economic damage from extreme weather and climate events have been steadily increasing since the 1930's in the United States (Changnon and Easterling 2000) and can be attributed to the increased vulnerability as population shifts to coastal areas (Kunkel et al. 1999). There is also considerable evidence that shifts in the frequency of extremes will occur with changes in climate, thus exposing additional segments of the population and infrastructure in harm's way (Easterling et al. 2000). Projects under this theme fill several of the gaps in knowledge needed to assess the frequency, intensity and impacts of extreme events, including downscaling and characterization of extreme events in climate models, decision-making and extreme events, and application of extreme value theory to improve the characterization of extreme events from meteorological data sets.


Theme 3: The Role of Climate in Human Health

The Role of Climate in Human HealthThe area of the human health impacts of climate is complex, requiring the interdisciplinary efforts of health professionals, climatologists, biologists, and social scientists to analyze the myriad relationships among physical, biological, ecological, and social systems relevant to health impacts. This is an impact area where an integrated assessment framework is obviously most needed Burke et al., 2001, Smolinski et al., 2003, McMichael et al., 2003). The goal of this theme is to develop a unique interdisciplinary research and educational program that will bring together leading institutions in health and climate science (i.e., NCAR, Johns Hopkins U, CDC). The theme has important connections to the other themes, including extreme events and characterizing uncertainty in the relationship between climate and health (McMichael, 2003).


Integrating Activities

The themes of uncertainty, extremes and climate and health contain key research gaps in advancing climate impact assessment science. However, in order for any scientific information to be useful in decision-making it must be credible, legitimate, and salient in the decision context at hand (Clark and Dickson 1999). This seemingly straightforward requirement contains a myriad of difficulties for bridging the science-society interface and effectively informing societal decisions. To address this challenging goal, the initiative will initiate a fourth component that will focus on decision-making specifically, examining the problem of uncertainty from the perspective of the decision-maker, as a complement to the scientific perspective in the themes listed above. The objectives of this component are to develop a systematic approach to determining where the decision-making environment is particularly sensitive to uncertainty in the information provided—i.e. when does uncertainty matter? This approach can be visualized as working backward from a given impact or decision-making problem to trace the information pathways relevant to the decision—jumping up backward through the "cascade of uncertainties" as it were. This initiative will examine the usefulness of an "end-to-end" characterization of uncertainty and alternate approaches in climate change research relevant to climate impacts and decision-making on various spatial scales (i.e. national/international policy through to regional and local resource management).



Burke, D. et al. 2001. Under the Weather: Climate, Ecosystems and Infectious Disease. National Academy Press: Washington DC. 146 pp.

Changnon SA, Easterling DR. 2000. U.S. Policies pertaining to weather and climate extremes. Science 289: 2053.

Clark W, Dickson N. 1999. The Global Environmental Assessment Project: Learning from efforts to link science and policy in an interdependent world. Acclimations 8:6-7.

Easterling DR, Meehl GA, Parmesan C, Changnon SA, Karl TR, Mearns LO. 2000. Climate Extremes: Observations, Modeling, and Impacts. Science 289: 2068-2074.

Kunkel K, Pielke Jr. R, Changnon S. 1999. Temporal fluctuations in weather and climate extremes that cause economic and human health impacts. Bull. Am. Meteorol. Soc. 80:1077.

McMichael, A. J. (ed.) 2003. Climate Change and Human Health: Risks and Responses. WHO:Geneva.

Moss RH, Schneider SH. 2000. Uncertainties in the IPCC TAR: Recommendations to lead authors for more consistent assessment reporting. In: Pachauri R, Taniguchi T and Tanaka, K. (eds.). Guidance papers on the cross cutting issues of the third assessment report, World Meteorological Organization, Geneva, pp.33-51.

Smolinski, M., Hamberg M, Lederberg J. (eds.), 2003: Microbial Threats to Health: Emergence, Detection, and Response. Inst. of Medicine, National Academy of Sciences. NAS Press: Washington 367 pp.

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NCAR Weather and Climate Impact Assessment Science Initiative