People across the United States are dealing with the impacts of climate change: Farmers and ranchers across the Great Plains battle drought, transportation planners consider how floods might affect roads and bridges, and utility managers try to keep the electricity flowing during heat waves.
The Third National Climate Assessment  (NCA), released May 6, 2014, is a compendium of the ways climate change affects our lives, livelihoods, and the economy in general. It describes how the climate has changed over the past century and provides a glimpse of future climate change and its impacts. The report also looks at how society is responding to a changing climate, and identifies actions we can take to prepare.
The NCA is a congressionally mandated report to the president and Congress that “analyzes the effects of global change on the natural environment, agriculture, energy production and use, land and water resources, transportation, human health and welfare, human social systems, and biological diversity.”
It’s a comprehensive synthesis describing how the climate has changed in different regions of the country, and the impacts to these regions and various sectors that scientists expect in the 21st century.
The report advances the concept of climate change as a “risk management” challenge, laying out the critical services, like access to water and energy, and natural resources likely to be disrupted or harmed by climate impacts.
The NCA can be a useful tool for public and private sector decision-makers trying to address climate challenges.
The report tells us that:
The report identifies opportunities for adaptation, advocating that actions taken now are likely to return greater benefits than actions taken in the future. In addition, the NCA notes that efforts to reduce greenhouse gas emissions are critical for limiting the amount and rate of future climate change, giving adaptation investments a better chance of success.
The report is divided into several large sections. We provide links to these portions of the report and a short description of each.
Overview and Report Findings : Summarizes the assessment and the 12 top-line messages of the report.
Our Changing Climate : Explores observed and projected climate change at the global and national scale. Discussion focuses on physical changes, such as temperature, precipitation, and sea level. Observations tend to cover the last 50 to 100 years, while projections extend through the 21st century. Many maps and graphs in this section are referenced throughout the report.
Regions : Discusses in depth the observed and projected impacts for specific U.S. regions.
Sectors : Explores how climate affects economic, social, or ecological resources, typically cutting across geographic boundaries.
Cross-cutting sectors : Investigates how some types of communities are affected by climate impacts, the interrelationships among many resource decisions, and the large-scale changes in biogeochemistry that accompany climate change. Many of these chapters were not in previous assessments.
Responses : Looks at solutions, as well as the research, data, and tools that will facilitate the implementation of solutions.
The NCA was written by 240 authors with diverse expertise and experience. They include academic researchers; local, state, and federal government officials; private sector leaders; and non-profit experts. Their efforts are coordinated by the U.S. Global Change Research Program (USGCRP), a collaboration of 13 federal science agencies. A 60-member federal advisory committee, the National Climate Assessment Development Advisory Committee (NCADAC), oversees the development of the NCA report and makes recommendations about the ongoing assessment process.
Previous assessments were released in 2000 and 2009. The latest update is expected to be the start of an ongoing process in collecting and disseminating data and information through various digital media and user networks.
The NCA is independent of reports issued by the Intergovernmental Panel on Climate Change (IPCC). Although both are based on the latest science, and reach similar conclusions, they differ significantly their scope and focus. Here are some key differences: