National Climate Assessment Strengthens Prevailing Climate Science and Identifies Impacts Across the U.S.

May 7, 2014

This week the Obama Administration released the third National Climate Assessment, a comprehensive report on climate change projections and impacts in the United States.  The report, which updates the second assessment from 2009, strengthens previous conclusions that climate change is occurring, primarily as a result of human activities. 

The report confirms that the trends already observed in temperature and precipitation changes have continued since the last assessment and will continue as a result of past greenhouse gas emissions.  Average temperatures are projected to increase 2 to 4 degrees over the next few decades as a result of past emissions, with temperature increases beyond that period dependent upon the level of emissions reductions in the coming decades.  Heavy precipitation and extreme heat events are increasing in a manner consistent with model projections. Impacts such as extreme weather events continue to vary in incidence and intensity regionally; for example, western states have experienced the most prevalent increases in intense heat waves, while eastern states have experienced more intense flood events.  Arctic ice is expected to continue melting as a result of rising temperatures, and sea levels are projected to rise an additional 1 to 4 feet by 2100.

The report provides an overview of the impacts of climate change on different sectors and regions within the United States.  It emphasizes that sectors are interconnected, and decision-making about climate change responses can affect vulnerabilities and resilience across multiple sectors.  In addition to chapters analyzing climate change impacts within single sectors such as water resources and transportation, the third assessment adds new chapters that focus on climate change interactions with multiple sectors, including: Energy, Water, and Land Use; Urban Systems, Infrastructure, and Vulnerability; Indigenous Peoples, Land and Resources; Land Use and Land Cover Change; Rural Communities; and Biogeochemical Cycles. 

The assessment also emphasizes that climate change is an overlay on natural climate variability. As a result, states are and will continue to experience differing types and magnitudes of impacts. The report contains separate chapters detailing current and future projected impacts for eight regions across the United States, as well as for Oceans and Marine Resources and Coastal Zone Development and Ecosystems generally.

The assessment includes three new chapters focused on processes and strategies for responding to climate change. The new Decision Support chapter discusses approaches for bridging the gap between scientists and decision-makers. The Mitigation chapter describes emissions trajectories, summarizes current efforts in the public and private sectors, and assesses the adequacy of ongoing activities to meet a low future emissions scenario. The Adaptation chapter summarizes current adaptation efforts in the public and private sectors, and describes adaptation processes and potential barriers, providing examples of local and regional efforts. Overall, the assessment indicates a general need for more aggressive implementation of mitigation and adaptation strategies to meet lower emissions scenarios and to adequately address climate-related risks. The report also identifies research needs for improving adaptation and mitigation activities, and decision-making generally.

In response to the accelerating pace of observed climate change impacts and a recognized need for ongoing efforts, the third assessment also envisions a new sustained process for assessing and communicating information on impacts, risks, and vulnerabilities associated with climate change.  This would supplement the existing quadrennial assessment process by providing more timely information on vulnerabilities and impacts to support decision-making, and by improving communication of this information to a broader audience through the network NCAnet.

Utilizing information contained in the third National Climate Assessment, the White House also developed and released fact sheets for all fifty states providing an overview of climate change impacts and projections and highlighting adaptation and mitigation efforts within each state.

The National Climate Assessment is conducted under the auspices of the Global Change Research Act of 1990 and is administered by the Global Change Research Program. The National Climate Assessment Draft Advisory Committee (NCADAC), a sixty-person Federal Advisory Committee supported by the National Oceanic and Atmospheric Administration (NOAA), produced a first draft of the report in January 2013 that was available for public comment until April 2013.

In preparing the draft, the NCADAC requested many technical input reports from teams of experts on all facets of climate impacts.  Georgetown Climate Center staff served as contributing authors for the technical input reports, including the 2012 technical input report on Coastal Impacts, Adaptation, and Vulnerabilities.  The Coastal Technical Input Report provides a detailed discussion of the vulnerabilities of coastal resources and development to climate change, and the report provides case studies of the adaptation efforts, tools and policies of that have been developed by many coastal states and localities.