Regions

The regional chapters (Chs. 21–30) assess current and future risks posed by climate change to each of the 10 NCA5 regions (Figure 1). These chapters provide detailed discussions of region-specific challenges, opportunities, and success stories for managing risks and impacts.

The Fifth National Climate Assessment explores subnational climate change risks, impacts, and responses in each of the 10 regions shown.

Figure 1. The map shows the 10 US regions that correspond to the 10 regional chapters of the report (Chs. 21–30). The same regional boundaries are used in text and figures throughout the Assessment to provide regional-scale information where appropriate. Adapted from USGCRP 2018.²

Likelihood

Virtually Certain	Very Likely	Likely	As Likely as Not	Unlikely	Very Unikely	Exceptionally Unlikely
99%–100%	90%–100%	66%–100%	33%–66%	0%–33%	0%–10%	0%–1%

Confidence Level

Very High	High	Medium	Low
Strong evidence (established theory, multiple sources, well-documented and accepted methods, etc.) High consensus	Moderate evidence (several sources, some consistency, methods vary and/or documentation limited, etc.) Medium consensus	Suggestive evidence (a few sources, limited consistency, methods emerging, etc.) Competing schools of thought	Inconclusive evidence (limited sources, extrapolations, inconsistent findings, poor documentation and/or methods not tested, etc.) Disagreement or lack of opinions among experts

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