摘要：The use of calibrated language in climate assessments has evolved over time and is an important tool for better characterizing climate risk. Despite improvements in communication, likelihood and confidence terms continue to be misinterpreted by nontechnical audiences. Public understanding of scientific certainty in climate impacts, particularly at the extreme tails of likelihood distribution, is inadequate. This study evaluates the use of calibrated language in the four most recent U.S. climate assessments. Across the assessments, there is inconsistent use, definition, location, and formatting designating a term as calibrated. Authors include additional, undefined certainty categories bridging qualitative confidence categories (e.g., "medium to high " ) and likelihood terms with no associated statistical value (e.g., "highly likely " ). Confidence and likelihood levels are more frequently reported for terms at the high end of certainty distributions, with at least 70% of all instances of confidence terms reporting high or very high confidence in three of the assessments. Almost all (>98%) likelihood language reported is in the likely (>66%) category or above and no likelihood terms below 50% are reported in any of the assessment's Key Messages. There is significant room for improvement in the representation of likelihood, as the word “likely” is frequently used with ambiguous intent; at least half of all instances of likelihood terms are used with noncalibrated, potentially colloquial intent in three of the assessments. The study concludes with a set of recommendations for improving the use of calibrated language and communication of risk in the development of future assessment products. Plain Language Abstract It is important for scientists to describe how certain they are about climate change science so that people can make informed decisions about how to reduce greenhouse gas emissions or prepare for climate impacts. Scientists who evaluate and summarize key findings from a broad review of climate change literature describe their certainty in these findings in scientific assessments using calibrated language. Calibrated language uses specific terminology to express varying degrees of confidence in a statement and how statistically likely an effect or impact is to occur. However, many people outside scientific fields are unfamiliar with calibrated language and often misinterpret their meaning. This study identifies three issues with how calibrated language is used in U.S. climate assessments. First, there is inconsistent use of calibrated language across reports, with authors sometimes using terms that are not defined. Second, these reports focus on findings with high confidence and high likelihood, potentially leaving out information on low probability but highly dangerous impacts. Finally, use of likelihood terms is particularly problematic because the word “likely” is commonly used as part of everyday conversation and different people assign different definitions to it based on their own language, culture, or field of work. It is therefore hard for readers to know, when they come across the word “likely,” whether that word is meant colloquially or whether it has a specific statistical definition associated with it. This paper suggests some ways in which future U.S. climate assessments can be improved to address these three issues.
关键词：climate assessments;uncertainty;calibrated language;likelihood;confidence;science communication
