finding 25.3 : key-message-25-3

Many coastal resources in the Southwest have been affected by sea level rise, ocean warming, and reduced ocean oxygen—all impacts of human-caused climate change (high confidence)—and ocean acidification resulting from human emissions of carbon dioxide (high confidence). Homes and other coastal infrastructure, marine flora and fauna, and people who depend on coastal resources face increased risks under continued climate change (high confidence).

This finding is from chapter 25 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

The authors examined the scientific literature in their areas of expertise. The team placed the highest weight on scientific articles published in refereed peer-reviewed journals. Other sources included published books, government technical reports, and, for data, government websites. The U.S. Global Change Research Program issued a public call for technical input and provided the authors with the submissions. The University of Arizona Center for Climate Adaptation Science and Solutions organized the Southwest Regional Stakeholder Engagement Workshop on January 28, 2017, with over 70 participants at the main location in Tucson, AZ, and dozens of participants in Albuquerque, NM, Boulder, CO, Davis, CA, Los Angeles, CA, Reno, NV, and Salt Lake City, UT, all connected by video. Participants included scientists and managers. The author team met the following day for their only meeting in person. Subsequently, authors held discussions in regular teleconferences. Many chapter authors met at the all-author meeting March 26–28, 2018, in Bethesda, MD.

Description of evidence base:

At the Golden Gate Bridge, San Francisco, sea level rose 9 ± 0.4 inches (22 ± 1 cm) from 1854 to 2016,8e1ab38d-5d31-4a6a-8ad6-e06fe74a4aa1 and at San Diego, 9 ± 0.8 inches (24 ± 2 cm) from 1906 to 2016.1f19738a-f4ec-4a51-8478-b88163d6dea6 Analyses of these gauges and hundreds around the world show a statistically significant increase in global mean sea level94a8514e-063e-45ef-b893-11c82b49a597,d7ed19d6-e5ac-4b44-b686-0a8a16fc431b due to melting of land ice and expansion of warming water caused by climate change.f03117be-ccfe-4f88-b70a-ffd4351b8190,dde395ae-d68c-4fdd-b3c8-d1ccbee85102 Measurements of sea surface temperatures from buoys off the California coast and around the world, combined with remote sensing data, have found warming of the top 75 m of ocean water at a rate of 2 ± 0.4°F (1.1 ± 0.2°C) per century from 1971 to 2010,88eb1d21-c245-468e-9508-33f3beebe215 caused by climate change.f03117be-ccfe-4f88-b70a-ffd4351b8190 Measurements and modeling of ocean acidity found an increase of acidity in the Pacific Ocean off San Diego of 25% to 40% (0.1 to 0.15 pH units) since 1750,6c7cce4a-0084-4f34-b1f4-c1c9f21981b3 caused by the increase of carbon dioxide in the atmosphere from cars, power plants, deforestation, and other human activities.f03117be-ccfe-4f88-b70a-ffd4351b8190 Measurements along the California coast have found ocean acidity during the core upwelling season (April to October) increasing by as much as four times (0.7 pH units) to some of the most acidic values in the world.21aa7761-7792-4b6a-b172-7fe3ecd83d13 Griggs et al. (2017)a1aee4ba-d4fc-4f92-a74a-e37189c138b5 project a median sea level rise of 19 inches (49 cm) and a range of 12–29 inches (30–73 cm; 67% probability) for the very low scenario (RCP2.6) and a median of 30 inches (76 cm) and a range of 19–41 inches (49–104 cm; 67% probability) for the higher scenario (RCP8.5) by the end of the century. On a similar timescale, Sweet et al. (2017)3bae2310-7572-47e2-99a4-9e4276764934 provide one map showing sea level rise projections for San Francisco, which shows a 39–47 inch (1–1.2 m) rise for the Intermediate scenario (approximately RCP8.5); the range for all of their scenarios is 0.3–2.5 m. Jevrejeva et al. (2016)4e1a8986-cfd0-4294-96ed-7e243d1d5091 project a sea level rise of 73 cm and a range of 12–74 inches (37–187 cm; 5% probability) for the higher scenario (RCP8.5) by 2100.

New information and remaining uncertainties:

Catastrophic rapid loss of Antarctic and Greenland ice sheets could increase sea level more rapidly. Sea level rise at individual locations depends on the form of the seafloor (bathymetry) and other local conditions. Climate change impacts compound overfishing and make fish populations more vulnerable. Potential economic changes in California’s coastal and marine-based economies are subject to many different environmental and socioeconomic factors.

The full complexity of ecological responses to ocean acidification in combination with other stresses in California marine waters is currently unknown. Food supply for marine species,cf677518-2ff0-4462-8d41-e48e8655ba18 natural variation in resilience,04a02114-e2b5-4c87-8c34-5658bc4f3c05,893d8808-72b4-4728-8759-76fd65dd724d and other environmental factors can affect the sensitivity of organisms to acidic conditions.

Assessment of confidence based on evidence:

Field measurements at numerous locations have detected sea level rise, ocean warming, ocean acidification, and ocean hypoxia. Multiple model-based analyses have attributed these changes to human-caused climate change, giving high confidence to these impacts of climate change.

This finding was derived from scenario rcp_8_5

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