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finding 1.6 : key-finding-1-6
Longer-term climate records over past centuries and millennia indicate that average temperatures in recent decades over much of the world have been much higher, and have risen faster during this time period, than at any time in the past 1,700 years or more, the time period for which the global distribution of surface temperatures can be reconstructed.
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. There has been an extensive increase in the understanding of past climates on our planet, including a number of new findings since NCA3.
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. There are many recent studies of the paleoclimate leading to this conclusion including those cited in the report (e.g., Mann et al. 2008;ade3fd09-603e-4fae-b252-1a4142392ea0 PAGE 2k Consortium 201389469262-7861-4aae-b33d-f8642174250e).
New information and remaining uncertainties: Despite the extensive increase in knowledge in the last few decades, there are still many uncertainties in understanding the hemispheric and global changes in climate over Earth’s history, including that of the last few millennia. Additional research efforts in this direction can help reduce those uncertainties.
Assessment of confidence based on evidence: There is high confidence for current temperatures to be higher than they have been in at least 1,700 years and perhaps much longer.
- Continental-scale temperature variability during the past two millennia (89469262)
- Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia (ade3fd09)
- Climate Change Impacts in the United States: The Third National Climate Assessment (dd5b893d)
- Climate Change 2013: The Physical Science Basis (f03117be)
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