This fact sheet draws information from the Global Climate Change Impacts in the United States report that describes how climate change affects coastal areas in the United States

U.S. Global Change Research Program

UNT (University of North Texas) Digital Library

Regional Highlights from  Global Climate Change Impacts in the United States www.globalchange.gov/usimpactsGlobal sea level has already risen due to the warming-induced expansion of the oceans, accelerated melting of most of the world’s glaciers, and loss of ice on the Greenland and Antarctic ice sheets. Sea level is currently rising at an increased rate. A warming climate will cause further sea-level rise over this century and beyond. Rising sea level is already eroding shorelines, drowning wetlands, and threatening homes, businesses, and infrastructure. The destructive potential of Atlantic hurricanes has increased in recent decades in association with increasing sea surface temperatures. In future decades, it is likely that hurricane rainfall and wind speeds will increase in response to global warming. Coastal water temperatures have risen and the distributions of marine species have shifted. Ocean acidification resulting from the uptake of carbon dioxide by ocean waters threatens corals, shellfish, and other living things that form their shells and skeletons from calcium carbonate. These and other forces converge and interact at the coasts, making these areas particularly sensitive to the impacts of climate change.Significant sea-level rise and storm surge will adversely affect coastal cities and ecosystems around the nation; low-lying and subsiding areas are most vulnerable.High rates of relative sea-level rise have already resulted in the loss of 1,900 square miles of Louisiana’s coastal wetlands during the past century, weakening their capacity to absorb the storm surge of hurricanes such as Katrina. Shoreline retreat is occurring along most of the nation’s exposed shores. Recent estimates of global sea-level rise are 3 to 4 feet in this century, with higher relative sea-level rise in areas where the land is subsiding (sinking), including most of the Atlantic Coast and Gulf Coast of the United States. More spring runoff and warmer coastal waters will increase the seasonal reduction in oxygen resulting from excess nitrogen from agriculture.Coastal “dead zones” with little or no oxygen in the water in the Chesapeake Bay and the Gulf of Mexico are likely to increase in size and intensity as warming increases. As dissolved oxygen levels decline below a certain threshold, living things cannot survive. They leave the area if they can, and die if they cannot. Coastal waters are projected to continue to warm by as much as 4 to 8°F in this century, resulting in a northward shift in the distribution of marine life along the coasts; this is already being observed. Dead Zones in the Chesapeake BayClimate change is likely to expand and intensify “dead zones,” areas where bottom water is depleted of dissolved oxygen because of nitrogen pollution, threatening living things.Key IssuesCoastsHigher water temperatures and ocean acidification due to increasing atmospheric carbon dioxide will present major additional stresses to coral reefs, resulting in significant die-offs and limited recovery.Carbon dioxide affects corals in at least two ways. The first results from warming, which causes corals to expel the symbiotic algae that live within them, nourish them, and give them their color. This is called coral bleaching, and eventually kills the corals if water temperatures remain elevated. The second effect results from carbon dioxide being absorbed by the oceans, acidifying the water. This reduces the ability of living things to create and maintain shells and skeletons. The effects on reef-building corals are likely to be particularly severe during this century.Changing ocean currents will affect coastal ecosystems.Recent changes in the California Current that bathes the entire Pacific Coast of the United States have resulted in increased upwelling of deeper ocean water along the coast. This has resulted in the emergence of oxygen-depletion events on the continental shelf off Oregon and Washington – a dead zone not directly caused by agricultural runoff and waste discharges such as those in the Chesapeake Bay and the Gulf of Mexico. Climate change affects coastal currents that moderate ocean temperatures and the productivity of ecosystems. As such, it is believed to be a factor in the low-oxygen “dead zone” that has appeared along the coast of Washington and Oregon in recent years.561 In the maps above, blue indicates low-oxygen areas and purple shows areas that are the most severely oxygen depleted.Pacific Coast “Dead Zone”2006 to 2007Bleached coralThe full report, including references for the material above, can be found online at:www.globalchange.gov/usimpactsIt is published by Cambridge University Press, with hard copies available at: www.cambridge.orgISBN 978-0-521-14407-0

Regional Highlights from Global Climate Change Impacts in the United States

This fact sheet draws highlights for Alaska from the Global Climate Change Impacts in the United States

Over the past 50 years, Alaska has warmed at more than twice the rate of the rest of the United States’ average. Its annual average temperature has increased 3.4°F, while winters have warmed by 6.3°F. The higher temperatures are already causing earlier spring snowmelt, reduced sea ice, widespread glacier retreat, and permafrost warming. The observed changes are consistent with climate model projections of greater warming over Alaska, especially in winter, as compared to the rest of the country. Climate models also project increases in precipitation over Alaska. Simultaneous increases in evaporation due to higher air temperatures, however, are expected to lead to drier conditions overall, with reduced soil moisture. Average annual temperatures are projected to rise between 5 and 13°F by late this century, with lower emissions scenarios yielding increases at the lower end of this range and higher emissions yielding increases near the higher end of the range.Longer summers and higher temperatures are causing drier conditions, even in the absence of strong trends in precipitation.Between 1970 and 2000, the snow-free season increased by about 10 days across Alaska, primarily due to earlier snowmelt in the spring. A longer growing season has potential benefits, such as a longer season for summer tourism and agriculture. However, the white spruce forests in Alaska’s interior are experiencing declining growth due to drought stress and continued warming could lead to widespread death of trees. The decreased soil moisture also suggests that agriculture might not benefit from the longer growing season.Insect outbreaks and wildfires are increasing with warming. During the 1990s, south-central Alaska experienced the largest outbreak of spruce beetles in the world as rising temperatures allowed the beetle to survive the winter and to complete its life cycle in half the usual time. Drought-stressed trees were unable to fight off the infestation. Fires are also increasing. By the end of this century, the area burned in Alaska is projected to triple under a moderate greenhouse gas emissions scenario and to quadruple under a higher emissions scenario.Regional Highlights from  Global Climate Change Impacts in the United States www.globalchange.gov/usimpactsWarming in Alaska has caused insect outbreaks to increase. Red areas indicate spruce beetle infestations on the Kenai Peninsula. Over 5 million acres of Alaska spruce forests were destroyed. Alaska Spruce Beetle Infestation Kenai Peninsula, 1972 to 1998Key IssuesAlaskaLakes are declining in area.Across the southern two-thirds of Alaska, the area of closed-basin lakes (lakes without stream inputs or outputs) has decreased over the past 50 years. This is likely due to the greater evaporation and thawing of permafrost that result from warming. These wetlands provide breeding habitat for millions of waterfowl and shorebirds and are important hunting and fishing grounds for Native People. A continued decline in the area of surface water would present challenges for ecosystems, natural resources, and the people who depend upon them. Coastal storms increase risks to villages and fishing fleets.Alaska has more coastline than the other 49 states combined. These coastlines are increasingly threatened by a combination of losing their protective sea ice buffer, increasing storm activity, and thawing coastal permafrost. The ground beneath some communities is literally crumbling into the sea. The rate of erosion along Alaska’s northeastern coastline has doubled over the past 50 years.Displacement of marine species will affect key fisheries.Climate change is altering marine ecosystems in ways that affect commercial fisheries. The world’s largest single fishery is the Bering Sea pollock  fishery, which has undergone major declines in recent years. Air and sea temperatures have increased, and sea ice has declined in this region.Thawing permafrost damages roads, runways, water and sewer systems, and other infrastructure.As permafrost thaws, the land can sink and collapse, damaging forests, homes, and infrastructure. Economists estimate that thawing permafrost will add billions of dollars in repair costs to public infrastructure (costs to private property have not yet been estimated). The full report, including references for the material above, can be found online at:www.globalchange.gov/usimpactsIt is published by Cambridge University Press, with hard copies available at: www.cambridge.orgISBN 978-0-521-14407-0Many of Alaska’s coastlines are eroding rapidly; the disappearance of coastal land is forcing communities to relocate. The 2007 line on the image indicates where Newtok, Alaska’s shoreline had eroded to by 2007. The other lines are projected assuming a conservative erosion rate of 36 to 83 feet per year; however, Newtok residents reported a July 2003 erosion rate of 110 feet per year. Projected Coastal Erosion, 2007 to 2027  Newtok, western Alaska

https://digital.library.unt.edu/ark:/67531/metadc29332/m2/1/high_res_d/CoastsFactSheet.pdf

Regional Highlights from Global Climate Change Impacts in the United States

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UNT (University of North Texas) Digital Library

UNT (University of North Texas) Digital Library