finding 16.4 : key-message-16-4

Shared resources along U.S. land and maritime borders provide direct benefits to Americans and are vulnerable to impacts from a changing climate, variability, and extremes (very likely, high confidence). Multinational frameworks that manage shared resources are increasingly incorporating climate risk in their transboundary decision-making processes.

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:

In the U.S.–Mexico drylands region, large areas are projected to become drier,37d85f6f-8d91-45e8-bf65-0ae8aee523a6 which will present increasing demands for water resources on top of existing stresses related to population growth.c9075dbc-f7c8-4d85-b534-e97282562b3e,143f2380-6a22-4149-a682-c10c62615d69 There is high confidence that resources critical to livelihoods at borders between the United States and neighboring nations are becoming increasingly vulnerable to impacts of climate change and that the multinational frameworks that manage these resources are increasingly incorporating research-based understanding of the climate risks that these resources face. The literature supporting the Key Message is substantial, increasing in quantity and robustness.5be5a1f9-7144-41ba-a80d-e3c77a49986f,212b019e-f046-40a4-bc19-5e752527fb1c,e1e1f3a0-9fea-4ad2-a3af-575716f9849e,9def246f-d97d-4cda-8794-78ceefe6b8da,49117baa-d1a6-475b-b5d5-7391a7c272b1,65b54f14-ed24-4e9f-a6f3-7589ba9b5160 The current impacts are well documented, and the projections of future impacts are aligned with the robust projections of future climate variability.69fe7cf7-52d4-4bc1-ba55-f6d994a47687,41c82d77-51be-4101-bd50-e773afc1ce1b The literature also provides examples of bilateral agreements and management frameworks in place to manage these resources. Examples of the impacts include the migration northward into Canadian waters of Pacific hake, a migratory species sensitive to water temperature, during periods of warmer water temperature.49117baa-d1a6-475b-b5d5-7391a7c272b1 One example of a bilateral management framework is the inclusion in 2012 of a climate change impacts annex to the U.S.–Canada Great Lakes Water Quality Agreement to identify, quantify, understand, and predict climate change impacts on the water quality of the Great Lakes.c3722455-6da6-40ca-aca3-6568594c80fe

New information and remaining uncertainties:

Impacts on shared resources along U.S. international borders are already being experienced. Uncertainties about the impacts are aligned with the uncertainties associated with projections of future climate variability. As elaborated upon in multiple regional chapters of this report (Ch. 18: Northeast; Ch. 20: U.S. Caribbean; Ch. 21: Midwest; Ch. 24: Northwest; Ch. 25: Southwest; Ch. 26: Alaska; Ch. 27: Hawai‘i & Pacific Islands), weather patterns in these border regions are projected to continue to change with varying degrees of likelihood and confidence.

Assessment of confidence based on evidence:

There is high confidence in the main message. There is sufficient empirical analysis on the relationships between past climate variations along U.S. international borders. The statement about the likelihood that impacts on shared resources will affect the bilateral frameworks established to manage these resources is based on expert understanding of the integration of climate risk into existing and future frameworks.

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