Climate Change Impact Assessments

Preparers

Linda Joyce, Rocky Mountain Research Station, US Forest Service, Fort Collins, CO, and Maria Janowiak, Northern Institute of Applied Climate Science, US Forest Service, Houghton, MI.

Issues

Climate change impact assessments seek to characterize, diagnose, and project risks or impacts of environmental change on people, communities, economic activities, infrastructure, ecosystems, or valued natural resources (1). Impact assessments have been requested at the national scale by US Congress (2) through the Global Change Research Act of 1990 which requires the National Science and Technology Council to analyze effects of global change on the natural environment, agriculture, energy, land and water resources, transportation, human health and welfare, human social systems, and biological diversity. Assessments have also been requested at more local scales by city officials such as Aspen, Colorado (3). Non-governmental organizations have also identified the value of impact assessments (4).

Impact assessments are motivated by the users' information needs and can be developed in multiple ways. An analysis often begins by examining changes to temperature, precipitation, and other climatic variables under multiple scenarios of greenhouse gas emissions (5). The analysis then considers the potential impacts on a geographic area, economic sector, community, or resource in order to provide information to managers, decision makers or policymakers. These assessments can focus on the synthesis of scientific information and may also include extensive quantitative analysis using models to explore the effects of a number of potential future climates. The development of an assessment often will involve a dialogue between those conducting the assessment and stakeholders. The assessments can be periodic (e.g., 6) or a one-time assessment (e.g., 3). A technical review by a set of independent experts will ensure that the summary statements and conclusions are well-supported in the scientific research and well-documented in the report.

Key Features

Impact assessments are typically the work of an interdisciplinary team. Generally, objectives are identified in concert with the institution or organization requesting the assessment. The scope of impact assessments vary. For example, the United States Global Change Research Program has developed a wide variety of assessment products, including an impact assessment for the entire United States (2) as well as many topical assessments on the carbon cycle (7), impacts to ecosystems (8), and other subjects. Other examples include impact assessments for the state of Pennsylvania (4) and the area surrounding Aspen, Colorado, (3) both of which contain information on projected changes in climate as well as potential impacts to communities, ecosystems, and locally important recreational activities. The system boundaries of the assessment affect the uncertainty in the analysis. Limits (e.g., time, funding, data availability, computational capacity) may influence the boundary definition. Broadly defined system boundaries may result in higher degree of generalization of system dynamics, whereas narrowly defined boundaries, allowing more detailed analysis, may limit the number of system influences considered. The interdisciplinary team defines system boundaries that are most likely to maximize the informational and decision-making value of the assessment.

Typically, the interdisciplinary team will synthesize several types of information, including scientific information from field studies and experimental studies, modeling experiments, and the knowledge of individuals with expertise in the system. If an analysis is to be a part of the assessment, the team identifies which climate scenarios to use, and which response models (e.g., vegetation, water, wildlife) to analyze the impacts of the changes in climate. For example, the climate impact study for the State of Washington conducted an analysis of 20 global climate model projections for the Pacific Northwest area and explored the projections of two regional climate models (9). This type of analysis deepens the understanding of current climate and model capability to capture these dynamics, and provides a range of projected climates on which to base the impacts analysis. The types of models available to explore the effects of climate change on vegetation, wildlife, and water vary. They reflect the current capacity of the science to quantify such impacts. Qualitative or conceptual analyses are also useful to explore impacts. For example, interviews with stakeholders can help to identify the local effects of the changing climate and stressors interacting with those changes (10).

During the synthesis process, the authors will reach conclusions about the future climate and ensuing effects on the topics and area of interest. The authors can articulate a sense of the certainty of those conclusions as well as identify sources of irreducible uncertainty at present. The authors' confidence in the assessment conclusions are extremely valuable when included as part of the analysis The Intergovernmental Panel on Climate Change (IPCC) has consistently refined its language to describe the certainty of the conclusions presented in its assessments. The 2007 IPCC reports were explicit about the language they used in describing uncertainty and levels of confidence in climate change (6, 11). The description of the author's certainty in the conclusions is a critical component of the assessment, especially when interacting with stakeholders.

The impact assessment may engage stakeholder groups to further broaden and deepen the key issues identified by those requesting the assessment (e.g. decision makers, policy makers, or managers). The engagement with stakeholders can occur through through mail or phone surveys, small workshops or public meetings. Stakeholders could include other public and private decision makers, resource and environmental managers, and the general public. Such discussions begin to bridge the scientific information with user needs and questions. These meetings can also be used as an initial opportunity for developing options to address the effects of climate change.

An independent review process ensures the scientific rigor of the impact assessment. Depending upon the nature and depth of the review, the process can be highly publicized with governmental oversight or more similar to a refereed journal review where the journal editor requests reviews by scientific peers. In both cases, the assessment authors must respond to the reviewers' comments in a revision. The process of developing the individual documents within the Fourth IPCC report involved several steps of review including two scientific reviews. For the 2007 IPCC Working Group I report, more than 30,000 comments were submitted by more than 650 individual experts, as well as governments and international organizations (6). Review editors were required to ensure that all substantive government and expert review comments received appropriate consideration.

Impact assessments offer fundamental scientific information about the potential consequences of climate change for a subject specified by the user. This information allows managers and decision makers to begin consideration of potential responses to these consequences. Typically these climate impact assessments have not included a full exploration of the capacity of the ecosystem or institution to cope or adapt to climate change nor have they included an exploration of potential management options. Vulnerability assessments can be used to explore capacity to adapt and management options, and may be used in place of or in addition to climate change impacts assessments.