[In this series, BNA’s climate blog takes a closer look at U.S. regions covered in the draft National Climate Assessment. In addition to Hawaii and U.S Affiliated Pacific Islands, regions covered in the assessment include the Southeast and Caribbean, Great Plains, Northeast, Northwest, Midwest, Southwest, and Alaska and the Arctic.]

Sea-level rise, ocean acidification, and other stressors related to climate change likely will force populations living in low-lying areas in Hawaii and on other Pacific Islands to migrate to higher elevations and continents, according to the draft National Climate Assessment.

Furthermore, sea-level rise could lead to losses in Hawaii’s tourism industry, which comprises 26 percent of the state’s economy, with a potential decline of $2 billion per year in visitor expenditures, according to the draft assessment. That’s because much of Hawaii’s infrastructure, such as airports and roads, are in low-lying areas that could be washed away as could such attractions as Waikiki beach.

As detailed in an Energy and Climate Report article published Jan. 11, the draft, released by the National Climate Assessment and Development Advisory Committee, is not yet an official federal document. It will become so once it’s submitted to the National Science and Technology Council sometime this fall. The council is expected to review, modify, and approve a final draft by Jan. 30, 2014.

A national assessment on climate science and climate change impacts is due to Congress every four years under the Global Change Research Act of 1990. However, only two reports have been completed since the law passed, one in 2000 and the other in 2009.

In addition to Hawaii, the U.S. Pacific Islands includes the territories of Guam and American Samoa, the Commonwealth of the Northern Mariana Islands, the Republic of Palau, the Federated States of Micronesia, and the Republic of Marshall Islands.

The region is vast—comprising more than 2,000 islands spanning millions of miles of ocean. It also is geologically diverse, made up of “volcanic islands, islands of continental crust, atolls, limestone islands, and islands of mixed geologic origin,” according to the draft assessment.

Temperature, Precipitation

Due to a host of factors, including natural climate cycles such as El Niño and La Niña, trade winds, and sea surface temperatures, the draft assessment said it’s difficult to predict long-term changes in temperature that may occur due to climate change.

However, the draft said modeling suggests that by 2055, temperatures in Hawaii and the Central North Pacific will increase between 1.5 degrees Fahrenheit if greenhouse gases decrease and 3.5 F if emissions continue to increase. In the Western North Pacific, the projected increases range from 1.9 F to 2.6 F, and in the Central South Pacific, from 1.9 F to 2.5 F under a scenario of either an increase or decrease in emissions.

In comparison, the draft estimates that, on average, U.S. temperatures will rise between 2 and 4 F by mid-century under current emission trends, and up to 5 to 10 F assuming continued increases in greenhouse gas emissions.

The draft assessment said uncertainty concerning future precipitation is even greater than predicted changes in temperature. In the last 100 years, and especially in recent decades, precipitation has trended downward, the draft said.

Under one scenario based on statistical downscaling, which is used to convert global-scale output to regional-scale conditions, precipitation in Hawaii is expected to decrease between 5 and 10 percent during the wet season and increase 5 percent during the dry season.

Sea-Level, Ocean Acidification

By 2100, sea- level in the Pacific region is expected to rise at the same rate as projected in the draft assessment for global sea-rise, which includes four possible scenarios—ranging from 8 inches to 6.6 feet. The lowest 8-inch-rise scenario is based on historic rates of observed sea-level change. A 1.6-foot rise is based on projected ocean warming. A 3.9-foot rise is based on projected ocean warming and recent ice sheet loss. A 6.6-foot rise reflects ocean warming and the maximum plausible contribution of ice-sheet loss and glacial melting.

Rising sea levels, coupled with tropical storms, will also increase coastal flooding and erosion, harming agriculture, ecosystems, and infrastructure, the draft said.

The first to feel the impact likely will be low-lying islands, such as the Namdrik Atoll in the Republic of the Marshall Islands, according to the draft. The atoll only has a land area of 1.1 square miles and a maximum elevation of 10 feet. It may be among the first “to face the possibility of climate-induced human migration as sea level continues to rise,” the draft said.

Migration will affect the ability of low-lying island populations to sustain customs and languages, and will raise challenges for migrants, for example, to find work and housing, the draft said. Communities also will be stressed as they will have to provide more infrastructure and services to absorb new population growth.

Ocean Temperatures, Acidification

Sea surface temperatures are projected to increase by up to 4.7 F if greenhouse gases continue to increase. Also, as the ocean continues to absorb carbon dioxide, acidification, which has increased by about 26 percent since the pre-industrial era, is expected to increase by 37 to 50 percent from present levels by 2100, the draft said.

The bleaching of coral reefs as the result of higher ocean temperatures is expected to continue and result in declines in the number and species of reef fishes. Even if there is a substantial reduction in greenhouse gas emissions, reefs may lose as much as 40 percent of their fish at mounting economic costs, the draft assessment said. For example, coral reefs in Hawaii provide an estimated $385 million in goods and services annually.

Freshwater Resources

Changes to freshwater resources will vary across the region due to differing island size and topography which will affect the storage of water. On most islands, however, the draft said increased temperatures, along with decreased rainfall, increased drought, and salt water intrusion due to sea-level rise will require more freshwater for drinking and irrigation.

Adaptation Planning

Hawaii and other larger islands have adaptation planning underway and smaller islands have worked with regional organizations to develop adaptation plans and access international resources, according to the draft. However, “very little research” has been done on the effectiveness of adaptation strategies.

Ending on a positive note, the draft assessment said, “The regional culture of communication and collaboration provides a strong foundation for adaptation planning and will be important for building resilience in the face of the changing climate.”