23 November 2018: The US Global Change Research Programme has released the second volume of the Fourth National Climate Assessment (NCA4 2018) titled, ‘Impacts, Risks and Adaptation in the United States,’ which assesses a range of potential climate change-related impacts, with an aim of helping decision makers identify risks that can be avoided or reduced.

The report, which was released on 23 November 2018, examines the impacts, including economic impacts, US residents can expect without urgent and significant action to address climate change. It also seeks help decision makers, utility and resource managers, public health officials, emergency planners and other stakeholders better understand these impacts. Thirteen federal agencies contribute to the NCA using the best available science to help the country understand, assess, predict and respond to climate change.

The report concludes that climate change-related impacts, including high temperatures, rising sea levels, deadly wildfires, torrential rainfalls and hurricanes, will worsen. Annual losses in some sectors are projected to exceed US$100 billion by the end of the century, without urgent mitigation and adaptation actions by federal, state and local governments. The report also finds that low-income communities, communities of color and indigenous peoples are affected the most. The report notes that annual average temperatures have increased by 1°C across the US since the beginning of the 20th century, and that annual median sea level along the US coast has risen by about nine inches since the early 20th century.

Mitigation and adaptation efforts lag behind the required level to avoid damages to the economy, environment and human health.

The full report addresses all US regions and economic sectors, and includes 16 topic chapters, ten regional chapters and two chapters focusing on mitigation and adaptation response strategies. The report finds that, inter alia:

• without global mitigation and regional adaptation efforts, climate change is expected to lead to increased losses to infrastructure and property and impede economic growth;
• mitigation and adaptation efforts lag behind the required level to avoid damages to the economy, environment and human health;
• impacts on water quality and quantity are increasing risks and costs to agriculture, energy production, industry, recreation and the environment;
• climate change is increasingly threatening indigenous communities’ livelihoods, economies, health and cultural identities by disrupting interconnected social, physical and ecological systems;
• without adaptation, climate change will continue to degrade infrastructure performance, with the potential for impacts that threaten national security and essential services, among others; and
• many communities will suffer financial impacts as high-tide flooding leads to higher costs and lower property values.

The report specifically discusses impacts on: ecosystems and ecosystem services; tourism and recreation; energy supply, delivery and demand; land cover and land-use change; forests; oceans and marine resources; urban systems and cities; rural communities; transportation; air quality; and tribes and indigenous peoples. It also addresses climate impacts on US international interests, and sector interactions, multiple stressors and complex systems.

This report builds on the NCA4 first volume, the ‘Climate Science Special Report’ (CSSR), released in November 2017, which provides the scientific basis for the second volume of NCA4 and describes observed climate trends and projections for temperature, precipitation, sea level rise and Arctic sea ice. [Publication: NCA 2018 Volume II: Impacts, Risks and Adaptation in the United States] [Report-in-Brief] [Summary Findings] [NOAA Media Advisory]