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 CSSR 5OD: FINAL CLEARANCE

Front Matter

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models used in this assessment ends in that year.

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For future projections, 30-year periods are again used for consistency. Projections are centered around 2030, 2050, and 2085 with an interval of plus and minus 15 years (for example, results for 2030 cover the period 2015–2045); Most model runs used here only project out to 2100 for future scenarios, but where possible, results beyond 2100 are shown. Note that these time periods are different than those used in some of the graphics in NCA3. There are also exceptions for graphics that are based on existing publications.

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For global results that may be dependent on findings from other assessments (such as those produced by the Intergovernmental Panel on Climate Change, or IPCC), and for other graphics that depend on specific published work, the use of other time periods was also allowed, but an attempt was made to keep them as similar to the selected periods as possible. For example, in the discussion of radiative forcing, the report uses the standard analyses from IPCC for the industrial era (1750 to 2011) (following IPCC 2013a). And, of course, the paleoclimatic discussion of past climates goes back much further in time.

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Model Results: Past Trends and Projected Futures

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The NCA3 included global modeling results from both the CMIP3 (Coupled Model Intercomparison Project, 3rd phase) models used in the 2007 international assessment (IPCC 2007) and the CMIP5 (Coupled Model Intercomparison Project, Phase 5) models used in the more recent international assessment (IPCC 2013a). Here, the primary resource for this assessment is the more recent global model results and associated downscaled products from CMIP5. The CMIP5 models and the associated downscaled products are discussed in Chapter 4: Projections.

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Treatment of Uncertainties: Likelihoods, Confidence, and Risk Framing

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Throughout this report’s assessment of the scientific understanding of climate change, the authors have assessed to the fullest extent possible the state-of-the-art understanding of the science resulting from the information in the scientific literature to arrive at a series of findings referred to as Key Findings. The approach used to represent the extent of understanding represented in the Key Findings is done through two metrics:

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Confidence in the validity of a finding based on the type, amount, quality, strength, and consistency of evidence (such as mechanistic understanding, theory, data, models, and expert judgment); the skill, range, and consistency of model projections; and the degree of agreement within the body of literature.

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Likelihood, or probability of an effect or impact occurring, is based on measures of uncertainty expressed probabilistically (in other words, based on the degree of understanding or knowledge, e.g., resulting from evaluating statistical analyses of observations or model

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28 June 2017