finding 1.2 : key-finding-1-2

The frequency and intensity of extreme heat and heavy precipitation events are increasing in most continental regions of the world (very high confidence). These trends are consistent with expected physical responses to a warming climate. Climate model studies are also consistent with these trends, although models tend to underestimate the observed trends, especially for the increase in extreme precipitation events (very high confidence for temperature, high confidence for extreme precipitation). The frequency and intensity of extreme high temperature events are virtually certain to increase in the future as global temperature increases (high confidence). Extreme precipitation events will very likely continue to increase in frequency and intensity throughout most of the world (high confidence). Observed and projected trends for some other types of extreme events, such as floods, droughts, and severe storms, have more variable regional characteristics.

This finding is from chapter 1 of Climate Science Special Report: The Fourth National Climate Assessment: Volume I.

Process for developing key messages: The Key Finding and supporting text summarizes extensive evidence documented in the climate science peer-reviewed literature. The trends for extreme events that were described in the NCA3 and IPCC assessments have continued, and our understanding of the data and ability to evaluate the many facets of the climate system have increased substantially.

Description of evidence base: The Key Finding and supporting text summarizes extensive evidence documented in the climate science literature and are similar to statements made in previous national (NCA3)dd5b893d-4462-4bb3-9205-67b532919566 and internationalf03117be-ccfe-4f88-b70a-ffd4351b8190 assessments. The analyses of past trends and future projections in extreme events and the fact that models tend to underestimate the observed trends are also well substantiated through more recent peer-reviewed literature as well.47387ef7-a738-4137-872d-329bf20a7788 fe69e36b-d8ee-4a5f-ac48-cd62eb38ad8f 9b9e779a-651a-48ef-8145-2484e0c7df35 8be3c048-4605-4823-8ad9-143537b05065 6a85cf26-c057-4c91-b60e-9d9e58bbc41a a36df8f5-949c-412c-8371-e5a5b139c757 71b48514-03df-49be-9ea6-9dad532f0a63 b91893b4-24a8-46ba-b09a-013d462caf1b

New information and remaining uncertainties: Key remaining uncertainties relate to the precise magnitude and nature of changes at global, and particularly regional, scales, and especially for extreme events and our ability to simulate and attribute such changes using climate models. Innovative new approaches to climate data analysis, continued improvements in climate modeling, and instigation and maintenance of reference quality observation networks such as the U.S. Climate Reference Network ( all have the potential to reduce uncertainties.

Assessment of confidence based on evidence: There is very high confidence for the statements about past extreme changes in temperature and precipitation and high confidence for future projections, based on the observational evidence and physical understanding, that there are major trends in extreme events and significant projected changes for the future.

This finding was derived from figure -.2: Confidence / Likelihood

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