Summary Findings of the Fourth National Climate Assessment


On November 23, the latest National Climate Assessment, Fourth National Climate Assessment (NCA4), was released by the U.S. Global Research Program, as required by the Clean Air Act. The Assessment, comprising three volumes and 1600 pages, contains some rather bleak findings which the Report usefully summarizes. Here’s a description of these findings.

1.     Communities. The report states that “climate change creates new risks and exacerbates existing vulnerabilities in communities across the United States.” In particular, “more frequent and intense extreme weather and climate-related events” will continue to damage infrastructure , ecosystems and social systems. However, “global action” to significantly cut greenhouse gas emissions can substantially reduce these risks.

2.     Economy. Without substantial and sustained global mitigation, climate change is expected to cause growing losses to infrastructure and property and impede economic growth. While some aspects of the economy will prosper through a modestly warmer world, on the whole there will be a net damage to the American economy which could reach “hundreds of billions of dollars” by the end of this century.

3.     Interconnected Impacts. Climate change “presents risks to interconnected systems”—the natural, built, and social systems such as water resources, food production, energy and transportation and public health systems which often span regional and national boundaries.

4.     Actions to Reduce Risks. The ongoing efforts to mitigate the effects of climate change “do not approach the scale considered necessary to avoid substantial damages to the economy, environment and human health over the coming decades.”

5.     Water. Climate change is adversely affecting “the quality and quantity of water available for use by people and ecosystems across the country.” Changes in snowfalls and rainfall are leading to “mismatches” between water availability and needs in some regions. New water management strategies are welcome, but the report concludes that the implementation of such practices remains limited.

6.     Health. Impacts from climate change, in particular changes in temperature and precipitation increase air quality and health risks among the vulnerable segments of our population. In response, the report states that adaptation and mitigation policies and programs can reduce the number of injuries, illnesses and deaths from climate-related health outcomes.

7.     Indigenous Peoples. Climate change “increasingly threatens indigenous communities’ livelihoods that depend on natural resources for their economic, cultural and physical well-being.” The report notes that some tribes are taking mitigation actions on their lands such as the development of renewable energy.

8.     Ecosystems and Ecosystem Services. Ecosystems and the benefits they provide to society are being altered by climate change, and the report notes the damage inflicted on some coral reef and sea ecosystems. Many of these observed impacts “can only be avoided by significantly reducing global emissions of carbon dioxide and other greenhouse gases.”

9.     Agriculture. Rising temperatures, heat, drought wildfire and heavy downpours threaten agricultural productivity in the United States. The impact of these changes “put rural livelihoods at risk.”

10.     Infrastructure. The nation’s “aging and deteriorating infrastructure” is being further stressed by these climate change events. To combat this, “forward-looking infrastructure design, planning and operational measures can reduce the risks of these impacts.

11.     Oceans & Coasts. Such climate change consequences as rising water temperatures, ocean acidification, retreating artic sea levels, coastal erosion, and higher storm surges threaten the oceans, the coasts and their ecosystems, with the Atlantic and Gulf Coasts facing above-average risks. Corrective actions include well-timed adaptation measures and substantial and sustained reductions in global greenhouse gas emissions.

12.     Tourism and Recreation. Climate change threatens seasonal and outdoor economies that rely on tourism for their economic wellbeing. One hopeful “proactive measure” would be the use of projected stream temperatures to set priorities for fish conservation and thus reduce disruption to tourist economies and recreation.