This website is the digital version of the 2014 National Climate Assessment, produced in collaboration with the U.S. Global Change Research Program.

For the official version, please refer to the PDF in the downloads section. The downloadable PDF is the official version of the 2014 National Climate Assessment.

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Welcome to the National Climate Assessment

The National Climate Assessment summarizes the impacts of climate change on the United States, now and in the future.

A team of more than 300 experts guided by a 60-member Federal Advisory Committee produced the report, which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences.

Explore the effects of climate change
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Ocean waters are becoming warmer and more acidic, broadly affecting ocean circulation, chemistry, ecosystems, and marine life.

Explore oceans.



More acidic waters inhibit the formation of shells, skeletons, and coral reefs. Warmer waters harm coral reefs and alter the distribution, abundance, and productivity of many marine species. The rising temperature and changing chemistry of ocean water combine with other stresses, such as overfishing and coastal and marine pollution, to alter marine-based food production and harm fishing communities.

Key Message: Rising Ocean Temperatures

The rise in ocean temperature over the last century will persist into the future, with continued large impacts on climate, ocean circulation, chemistry, and ecosystems.

Key Message: Ocean Acidification Alters Marine Ecosystems

The ocean currently absorbs about a quarter of human-caused carbon dioxide emissions to the atmosphere, leading to ocean acidification that will alter marine ecosystems in dramatic yet uncertain ways.

Key Message: Habitat Loss Affects Marine Life

Significant habitat loss will continue to occur due to climate change for many species and areas, including Arctic and coral reef ecosystems, while habitat in other areas and for other species will expand. These changes will consequently alter the distribution, abundance, and productivity of many marine species.

Key Message: Rising Temperatures Linked to Diseases

Rising sea surface temperatures have been linked with increasing levels and ranges of diseases in humans and in marine life, including corals, abalones, oysters, fishes, and marine mammals.

Key Message: Economic Impacts of Marine-related Climate Change

Climate changes that result in conditions substantially different from recent history may significantly increase costs to businesses as well as disrupt public access and enjoyment of ocean areas.

Key Message: Initiatives Serve as a Model

In response to observed and projected climate impacts, some existing ocean policies, practices, and management efforts are incorporating climate change impacts. These initiatives can serve as models for other efforts and ultimately enable people and communities to adapt to changing ocean conditions.


Observed Ocean Warming Observed Ocean Warming Details/Download

As a nation, we depend on the oceans for seafood, recreation and tourism, cultural heritage, transportation of goods, and, increasingly, energy and other critical resources. The U.S. Exclusive Economic Zone extends 200 nautical miles seaward from the coasts, spanning an area about 1.7 times the land area of the continental United States. This vast region is host to a rich diversity of marine plants and animals and a wide range of ecosystems, from tropical coral reefs to Arctic waters covered with sea ice.

Oceans support vibrant economies and coastal communities with numerous businesses and jobs. More than 160 million people live in the coastal watershed counties of the United States, and population in this zone is expected to grow in the future. The oceans help regulate climate, absorb carbon dioxide, and strongly influence weather patterns far into the continental interior. Ocean issues touch all of us in both direct and indirect ways.11,12,13,14

Changing climate conditions are already affecting these valuable marine ecosystems and the array of resources and services we derive from the sea. Some climate trends, such as rising seawater temperatures and ocean acidification, are common across much of the coastal areas and open ocean worldwide. The biological responses to climate change often vary from region to region, depending on the different combinations of species, habitats, and other attributes of local systems.

Ocean Impacts of Increased Atmospheric Carbon Dioxide

Ocean Impacts of Increased Atmospheric Carbon Dioxide

As heat-trapping gases, primarily carbon dioxide (CO2) (panel A), have increased over the past decades, not only has air temperature increased worldwide, but so has the ocean surface temperature (panel B). The increased ocean temperature, combined with melting of glaciers and ice sheets on land, is leading to higher sea levels (panel C). Increased air and ocean temperatures are also causing the continued, dramatic decline in Arctic sea ice during the summer (panel D). Additionally, the ocean is becoming more acidic as increased atmospheric CO2 dissolves into it (panel E). (CO2 data from Etheridge 2010, Tans and Keeling 2012, and NOAA NCDC 2012; SST data from NOAA NCDC 2012 and Smith et al. 2008; Sea level data from CSIRO 2012 and Church and White 2011; Sea ice data from University of Illinois 2012; pH data from Doney et al. 20122,3,4,5,6,7,8,9).


The oceans cover more than two-thirds of the Earth’s surface and play a very important role in regulating the Earth’s climate and in climate change. Today, the world’s oceans absorb more than 90% of the heat trapped by increasing levels of CO2 and other greenhouse gases in the atmosphere due to human activities. This extra energy warms the ocean, causing it to expand and sea levels to rise. Of the global sea level rise observed over the last 35 years, about 40% is due to this warming of the water. Most of the rest is due to the melting of glaciers and ice sheets. Ocean levels are projected to rise another 1 to 4 feet over this century, with the precise number largely depending on the amount of global temperature rise and polar ice sheet melt.

Coral Bleaching Coral Bleaching Details/Download

Observations from past climate combined with climate model projections of the future suggest that over the next 100 years the Atlantic Ocean’s overturning circulation (known as the “Ocean Conveyor Belt”) could slow down as a result of climate change. These ocean currents carry warm water northward across the equator in the Atlantic Ocean, warming the North Atlantic (and Europe) and cooling the South Atlantic. A slowdown of the Conveyor Belt would increase regional sea level rise along the east coast of the U.S. and change temperature patterns in Europe and rainfall in Africa and the Americas, but would not lead to global cooling.

Warming ocean waters also affect marine ecosystems like coral reefs, which can be very sensitive to temperature changes. When water temperatures become too high, coral expel the algae (called zooxanthellae) which help nourish them and give them their vibrant color. This is known as coral bleaching. If the high temperatures persist, the coral die.


Ocean Acidification Reduces Size of Clams Ocean Acidification Reduces Size of Clams Details/Download

In addition to the warming, the acidity of seawater is increasing as a direct result of increasing atmospheric CO2. Due to human-induced emissions, atmospheric CO2 has risen by about 40% above pre-industrial levels.3,16 About a quarter of this excess CO2 has dissolved into the oceans, thereby changing seawater chemistry and decreasing pH (making seawater more acidic).13,17 There has been about a 30% increase in surface ocean acidity since pre-industrial times.18 Ocean acidification will continue in the future due to the interaction of atmospheric CO2 and ocean water. Regional differences in ocean pH occur as a result of variability in regional or local conditions, such as upwelling that brings subsurface waters up to the surface.19 Locally, coastal waters and estuaries can also exhibit acidification as the result of pollution and excess nutrient inputs.

More acidic waters create repercussions along the marine food chain. The chemical changes caused by the uptake of CO2 make it more difficult for living things to form and maintain calcium carbonate shells and skeletons and increases erosion of coral reefs,20,21 resulting in alterations in marine ecosystems that will become more severe as present-day trends in acidification continue or accelerate.22,23,24,25 Tropical corals are particularly susceptible to the combination of ocean acidification and ocean warming, which would threaten the rich and biologically diverse coral reef habitats.


fishing vessel ©
Fisheries Shifting North Fisheries Shifting North Details/Download

There has been a significant increase in reported incidences of disease in corals, urchins, mollusks, marine mammals, turtles, and echinoderms (a group of some 70,000 marine species including sea stars, sea urchins, and sand dollars) over the last several decades27,28,29,30,31,32 Increasing disease outbreaks in the ocean affecting ecologically important species, which provide critically important habitat for other species such as corals, algae, and eelgrass, have been linked with rising temperatures..28,33,34,35,36 Disease increases mortality and can reduce abundance for affected populations as well as fundamentally change ecosystems by altering habitat or species relationships. For example, loss of eelgrass beds due to disease can reduce critical nursery habitat for several species of commercially important fish.36,37


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  2. Bjork, M., F. Short, E. McLeod, and S. Beer, 2008: Managing Seagrasses for Resilience to Climate Change. World Conservation Union.

  3. Boyett, H. V., D. G. Bourne, and B. L. Willis, 2007: Elevated temperature and light enhance progression and spread of black band disease on staghorn corals of the Great Barrier Reef. Marine Biology, 151, 1711-1720, doi:10.1007/200227-006-0603-y.

  4. Bruno, J. F., E. R. Selig, K. S. Casey, C. A. Page, B. L. Willis, C. D. Harvell, H. Sweatman, and A. M. Melendy, 2007: Thermal stress and coral cover as drivers of coral disease outbreaks. PLoS Biology, 5, e124, doi:10.1371/journal.pbio.0050124.

  5. Case, R. J., S. R. Longford, A. H. Campbell, A. Low, N. Tujula, P. D. Steinberg, and S. Kjelleberg, 2011: Temperature induced bacterial virulence and bleaching disease in a chemically defended marine macroalga. Environmental Microbiology, 13, 529-537, doi:10.1111/j.1462-2920.02356.x.

  6. Chavez, F. P., M. Messié, and J. T. Pennington, 2011: Marine primary production in relation to climate variability and change. Annual Review of Marine Science, 3, 227-260, doi:10.1146/annurev.marine.010908.163917.

  7. Church, J. A., and N. J. White, 2011: Sea-level rise from the late 19th to the early 21st century. Surveys in Geophysics, 32, 585-602, doi:10.1007/s10712-011-9119-1.

  8. Cooley, S. R., H. L. Kite-Powell, L. Hauke, and S. C. Doney, 2009: Ocean acidification’s potential to alter global marine ecosystem services. Oceanography, 22, 172-181, doi:10.5670/oceanog.2009.106.

  9. CSIRO, 2012: The Commonwealth Scientific and Industrial Research Organisation. URL

  10. Doney, S. C., W. M. Balch, V. J. Fabry, and R. A. Feely, 2009: Ocean acidification: A critical emerging problem for the ocean sciences. Oceanography, 22, 16-25, doi:10.5670/oceanog.2009.93. URL

  11. Doney, S. C., M. Ruckelshaus, J. E. Duffy, J. P. Barry, F. Chan, C. A. English, H. M. Galindo, J. M. Grebmeier, A. B. Hollowed, N. Knowlton, J. Polovina, N. N. Rabalais, W. J. Sydeman, and L. D. Talley, 2012: Climate change impacts on marine ecosystems. Annual Review of Marine Science, 4, 11-37, doi:10.1146/annurev-marine-041911-111611. URL

  12. Eakin, C. M. et al., 2010: Caribbean corals in crisis: Record thermal stress, bleaching, and mortality in 2005. PLoS ONE, 5, e13969, doi:10.1371/journal.pone.0013969. URL

  13. Etheridge, D.M., et al., 2010: Law Dome Ice Core 2000-Year CO2, CH4, and N2O Data.

  14. Feely, R. A., S. C. Doney, and S. R. Cooley, 2009: Ocean acidification: Present conditions and future changes in a high-CO2 world. Oceanography, 22, 36-47, doi:10.5670/oceanog.2009.95. URL

  15. Feely, R. A., C. L. Sabine, J. M. Hernandez-Ayon, D. Ianson, and B. Hales, 2008: Evidence for upwelling of corrosive “acidified” water onto the continental shelf. Science, 320, 1490-1492, doi:10.1126/science.1155676. URL

  16. Harvell, D., S. Altizer, I. M. Cattadori, L. Harrington, and E. Weil, 2009: Climate change and wildlife diseases: When does the host matter the most? Ecology, 90, 912-920, doi:10.1890/08-0616.1.

  17. Hughes, J. E., L. A. Deegan, J. C. Wyda, M. J. Weaver, and A. Wright, 2002: The effects of eelgrass habitat loss on estuarine fish communities of southern New England. Estuaries and Coasts, 25, 235-249, doi:10.1007/BF02691311.

  18. Kroeker, K. J., R. L. Kordas, R. N. Crim, and G. G. Singh, 2010: Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms. Ecology Letters, 13, 1419-1434, doi:10.1111/j.1461-0248.2010.01518.x. URL

  19. Kroeker, K. J., R. L. Kordas, R. Crim, I. E. Hendriks, L. Ramajo, G. S. Singh, C. M. Duarte, and J. - P. Gattuso, 2013: Impacts of ocean acidification on marine organisms: Quantifying sensitivities and interaction with warming. Global Change Biology, 19, 1884-1896, doi:10.1111/gcb.12179. URL

  20. C. Meure, M. F., D. Etheridge, C. Trudinger, P. Steele, R. Langenfelds, and T. van Ommen, 2006: Law Dome CO2, CH4, and N2O ice core records extended to 2000 years BP. Geophysical Research Letters, 33, L14810, doi:10.1029/2006GL026152. URL

  21. Marshall, P., and H. Schuttenberg, 2006: A Reef Manager's Guide to Coral Bleaching. Great Barrier Reef Marine Park Authority, IUCN Global Marine Programme, and U.S. National Oceanic and Atmospheric Administration, 163 pp. URL

  22. NCDC, 2012: Extended Reconstructed Sea Surface Temperature. NOAA'S National Climatic Data Center. URL

  23. NMFS, 2012: Fisheries of the United States 2011. 139 pp., National Marine Fisheries Service, Office of Science and Technology, Silver Spring, MD. URL

  24. NOC, 2012: National Ocean Policy Draft Implementation Plan. 118 pp., National Ocean Council, Washington, D.C. URL

  25. NRC, 2010: Ocean Acidification. A National Strategy to Meet the Challenges of a Changing Ocean. 175 pp., Committee on the Development of an Integrated Science Strategy for Ocean Acidification Monitoring Research and Impacts Assessment, Ocean Studies Board, Division on Earth and Life Studies, National Research Council, Washington, D.C. URL

  26. Pinsky, M. L., and M. Fogarty, 2012: Lagged social-ecological responses to climate and range shifts in fisheries. Climatic Change, 115, 883-891, doi:10.1007/s10584-012-0599-x.

  27. Sabine, C. L., R. A. Feely, N. Gruber, R. M. Key, K. Lee, J. L. Bullister, R. Wanninkhof, C. S. Wong, D. W. R. Wallace, B. Tilbrook, F. J. Millero, T. - H. Peng, A. Kozyr, T. Ono, and A. F. Rios, 2004: The oceanic sink for anthropogenic CO2. Science, 305, 367-371, doi:10.1126/science.1097403.

  28. Smith, T. M., R. W. Reynolds, T. C. Peterson, and J. Lawrimore, 2008: Improvements to NOAA’s historical merged land-ocean surface temperature analysis (1880-2006). Journal of Climate, 21, 2283-2296, doi:10.1175/2007JCLI2100.1.

  29. Staehli, A., R. Schaerer, K. Hoelzle, and G. Ribi, 2009: Temperature induced disease in the starfish Astropecten jonstoni. Marine Biodiversity Records, 2, e78, doi:10.1017/S1755267209000633. URL

  30. Talmage, S. C., and C. J. Gobler, 2010: Effects of past, present, and future ocean carbon dioxide concentrations on the growth and survival of larval shellfish. Proceedings of the National Academy of Sciences, 107, 17246-17251, doi:10.1073/pnas.0913804107. URL

  31. Tans, P., and R. Keeling, 2012: Trends in Atmospheric Carbon Dioxide, Full Mauna Loa CO2 Record. NOAA’s Earth System Research Laboratory. URL

  32. Tribollet, A., C. Godinot, M. Atkinson, and C. Langdon, 2009: Effects of elevated pCO2 on dissolution of coral carbonates by microbial euendoliths. Global Biogeochemical Cycles, 23, GB3008, doi:10.1029/2008GB003286.

  33. U.S. Commission on Ocean Policy, 2004: An Ocean Blueprint for the 21st Century: Final Report. 28 pp., U.S. Commission on Ocean Policy, Washington, D.C. URL

  34. University of Illinois, 2012: Sea Ice Dataset. 2012. URL

  35. Ward, J. R., and K. D. Lafferty, 2004: The elusive baseline of marine disease: Are diseases in ocean ecosystems increasing? PLoS Biology, 2, e120, doi:10.1371/journal.pbio.0020120.

  36. Ward, J. R., K. Kim, and C. D. Harvell, 2007: Temperature affects coral disease resistance and pathogen growth. Marine Ecology Progress Series, 329, 115-121, doi:10.3354/meps329115.

  37. Wisshak, M., C. H. L. Schönberg, A. Form, and A. Freiwald, 2012: Ocean acidification accelerates reef bioerosion. PLoS ONE, 7, e45124, doi:10.1371/journal.pone.0045124. URL

The National Climate Assessment summarizes the impacts of climate change on the United States, now and in the future.

A team of more than 300 experts guided by a 60-member Federal Advisory Committee produced the report, which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences.

United States Global Change Research Program logo United States Global Change Research Program participating agency logos