Strained freshwater supplies, damaged coastal infrastructure, coral reef death, and greater stresses on biodiversity and native species were among the major concerns and challenges detailed in the Hawai‘i-Pacific Islands chapter of the Fourth National Climate Assessment (NCA4). In economic terms, the impacts add up to billions of dollars. The assessment found that early action to address these impacts can lower economic, environmental, social, and cultural costs and could help to prevent displacement from lands and resources.

NCA4 Volume II, Impacts, Risks, and Adaptation in the United States is the nation’s comprehensive, authoritative report on the effects of climate change on U.S. communities and the economy. Released in November 2018, the report’s findings were covered in more than 140 front-page newspaper stories in the U.S.

In Hawai‘i, the assessment reinforced sea level rise guidance and planning already underway within the City and County of Honolulu. Some officials see its findings as further validation that they must act now to protect citizens.

National Climate Assessment’s Findings for Hawai‘i

Chapter 27 of NCA4 details the changes that Hawai‘i and U.S.-Affiliated Pacific Islands are already feeling, as well as what lies ahead. The top findings include:

• Dependable and safe water supplies are threatened by rising temperatures, changing rainfall patterns, sea level rise, and increased risk of extreme drought and flooding. Islands are already experiencing saltwater contamination due to sea level rise, which is expected to catastrophically impact food and water security, especially on low-lying atolls.
• Sea level rise has accelerated and is now damaging critical infrastructure such as transportation and housing, as well as beaches, ecosystems and cultural sites. In Hawai‘i, the value of all structures and land expected to be flooded by 2100 amounts to more than $19 billion statewide. The Pacific Islands will experience sea level rise higher than the global average, projected to accelerate strongly after mid-century. Adaptation strategies that are implemented sooner can better prepare communities and infrastructure.
• Increasing ocean temperatures and acidification threaten fisheries, coral reefs, and the livelihoods they support. Widespread coral reef bleaching and death are occurring more frequently, and by mid-century these events are projected to occur annually, especially if current trends in greenhouse gas emissions continue. Bleaching and acidification will result in loss of reefs, leading to lower fisheries yields and loss of coastal protection and habitat.
• These changes imperil Indigenous peoples’ health and well-being and their relationships with lands, territories, and cultural resources.
• Climate change reduces the ability of habitats to support protected plant and animal species. Changes promote the spread of invasive species while threatening biodiversity, which is important to island people and local economies. Some species are expected to become extinct and others to decline to the point of requiring costly protection.

Honolulu Mayor Responds, Highlighting Costs of Sea Level Rise

For Honolulu Mayor Kirk Caldwell, the coastal infrastructure impacts and potential economic loss from sea level rise that NCA4 calls attention to are sobering. Managing sea level rise is already a reality for the City and County of Honolulu, where coastal erosion and high tide flooding is worsening as a result. At the release of NCA4, Mayor Caldwell held a press conference with NCA4 authors at Honolulu Harbor to underscore the findings for Hawai‘i. “There is no more important issue” Mayor Caldwell said at the press conference, speaking about climate change and what it means for O‘ahu homes, roads, and other infrastructure.

As the City and County of Honolulu’s adaptation responses to sea level rise take shape, the National Climate Assessment has reinforced new guidance. The mayor, on the advice of the Honolulu Climate Change Commission, recently directed all city departments and agencies to take action to minimize the risks from, and adapt to the impacts of climate change and sea level rise. The directive requires entities under the mayor’s jurisdiction to plan for: extreme high tide flooding associated with 3.2 feet of sea level rise by mid-century and to consider 6 feet of sea level rise in later decades of the century for large infrastructure projects. The five-member advisory Honolulu Climate Change Commission includes two NCA4 authors. Frequent and ongoing communication among a community of technical experts, public stakeholders, and Honolulu officials is key to enabling the implementation of these science-based guidelines.

About the Fourth National Climate Assessment

Mandated in the Global Change Research Act passed by Congress in 1990, the National Climate Assessment synthesizes the state of climate knowledge and assesses climate change impacts, risks, and adaptation across the U.S. every four years. The main objective is to help Americans better identify, avoid, and/or reduce climate-related risks. The National Climate Assessment process relies on consensus and undergoes extensive review.

Volume II of the Fourth National Climate Assessment builds upon the physical science assessment presented in Volume I, the Climate Science Special Report, released in November 2017. Vol. II places a strong emphasis on regional information, addressing the impacts of climate change on 10 regions of the United States.

More than 300 Federal and non-Federal authors representing a range of expertise wrote the report. The Hawai‘i and Pacific Islands chapter has 11 authors and 77 regional contributors, and is backed by more than 250 citations from published articles, reports, and books.

For further information, please contact Zena Grecni, Sustained Climate Assessment Specialist at the East-West Center.