finding 16.1 : key-message-16-1

The impacts of climate change, variability, and extreme events outside the United States are affecting and are virtually certain to increasingly affect U.S. trade and economy, including import and export prices and businesses with overseas operations and supply chains (very likely, medium confidence).

This finding is from chapter 16 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

The Fourth National Climate Assessment (NCA4) is the first U.S. National Climate Assessment (NCA) to include a chapter that addresses the impacts of climate change beyond the borders of the United States. This chapter was included in NCA4 in response to comments received during public review of the Third National Climate Assessment (NCA3) that proposed that future NCAs include an analysis of international impacts of climate change as they relate to U.S. interests.

This chapter focuses on the implications of international impacts of climate change on U.S. interests. It does not address or summarize all international impacts of climate change; that very broad topic is covered by Working Group II of the Intergovernmental Panel on Climate Change (IPCC; e.g., IPCC 2014c390e13f-8517-40a9-a236-ac4dede3a7a0). The U.S. government supports and participates in the IPCC process. The more focused topic of how U.S. interests can be affected by climate impacts outside of the United States is not specifically addressed by the IPCC.

The topics in the chapter—economics and trade, international development and humanitarian assistance, national security, and transboundary resources—were selected because they illustrate ways in which U.S. interests can be affected by international climate impacts. These topics cut across the world, so the chapter does not focus on impacts in specific regions.

The transboundary section was added to address climate-related impacts across U.S. borders. While the regional chapters address local and regional transboundary impacts, they do not address impacts that exist in multiple regions or agreements between the United States and its neighbors that create mechanisms for addressing such impacts.

The science section is part of the chapter because of the importance of international scientific cooperation to our understanding of climate science. That topic is not treated as a separate section because it is not a risk-based issue and therefore not an appropriate candidate to have as a Key Message.

The U.S. Global Change Research Program (USGCRP) put out a call for authors for the International chapter both inside and outside the Federal Government. The USGCRP asked for nominations of and by individuals with experience and knowledge on international climate change impacts and implications for the United States as well as experience in assessments such as the NCA.

All of the authors selected for the chapter have extensive experience in international climate change, and several had been authors on past NCAs. Section lead assignments were made based on the expertise of the individuals and, for those authors who are current federal employees, based on the expertise of the agencies. The author team of ten individuals is evenly divided between federal and non-federal personnel.

The coordinating lead author (CLA) and USGCRP organized two public outreach meetings. The first meeting was held at the Wilson Center in Washington, DC, on September 15, 2016, as part of the U.S. Agency for International Development’s (USAID) Adaptation Community Meetings and solicited input on the outline of the chapter and asked for volunteers to become chapter authors or otherwise contribute to the chapter. A public review meeting regarding the International chapter was held on April 6, 2017, at Chemonics in Washington, DC, also as part of USAID’s Adaptation Community Meetings series. The USGCRP and chapter authors shared information about the progress to date of the International chapter and sought input from stakeholders to help inform further development of the chapter, as well as to raise general awareness of the process and timeline for NCA4.

The chapter was revised in response to comments from the public and from the National Academy of Sciences. The comments were reviewed and discussed by the entire author team and the review editor, Dr. Diana Liverman of the University of Arizona. Individual authors drafted responses to comments on their sections, while the CLA and the chapter lead (CL) drafted responses to comments that pertained to the entire chapter. All comments were reviewed by the CLA and CL. The review editor reviewed responses to comments and revisions to the chapter to ensure that all comments had been considered by the authors.

Description of evidence base:

Major U.S. firms are concerned about potential climate change impacts to their business (e.g., Peace et al. 2013, Peace and Maher 2015274b75cc-ce53-436a-b971-99fe1d9b371f,6293e798-6b97-452e-b9e2-25022e0af38a and illustrative examples of SEC filings describing climate risks to U.S. companies operating abroad715696f5-157d-41b3-8a32-03f41449f883,2fb02cef-b95f-4d8d-b6a7-e1e69c7706e1,24e784d9-009b-4d88-b96f-768e99d1c4fb,3f250149-4f9e-49e9-9b93-47b16c9201f5). Examples include the 2011 food price spike076458a1-018a-4056-b943-e178110f0726,8a806e30-5627-4d0e-a6ba-2d58ef221f1b and the 2011 Bangkok flooding; corresponding prolonged and cascading impacts to transportation and supply chains are documented in the citations related to those issues.b9024cb0-0df4-45a9-8cfa-f22f55a2bd40,197d3eac-636e-4579-ba44-915778bf24a9,059a31f7-7dd5-4088-b1c1-0c353f18cf3b Future changes in precipitation, temperature, and sea level (among other factors) are very likely, as described in USGCRP,75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1 and are very likely to exacerbate impacts on the U.S. economy and trade, relative to past impacts.

New information and remaining uncertainties:

The literature base on the impacts of climate change outside U.S. borders to the U.S. economy and trade is significantly smaller than that on climate change impacts within U.S. borders. In particular, few studies have attempted to quantify the magnitude of the past impacts of climate variability and change that occur outside the United States on U.S. economics and trade. Since there is limited literature, it is unclear how climate-driven regional shifts in economic activity will affect U.S. economics and trade. Nonetheless, the general nature of the main types of impacts described in this section are relatively well known.

Assessment of confidence based on evidence:

The portion of the main message pertaining to the future is very likely due to the likelihood of future climate change75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1 and persistence of the sensitivity of the U.S. economy and its trade to climate conditions. There is medium confidence that climate change and extremes outside the United States are impacting and will increasingly impact our trade and economy because there is insufficient empirical analysis on the causal relationships between past international climate variations outside the United States and U.S. economics and trade to provide higher confidence at this time. No attempt was made in this chapter to define the net impact of international climate change on the U.S. economy and trade; such a statement would have had very low confidence due to the current paucity of quantitative analyses.

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