Marine & Coastal Climatic Changes & Impacts

Climate change alters the ability of marine and coastal ecosystems to function and provide the goods and services upon which species and humans depend. These ecosystem services include food, fresh water, flood and erosion control, climate sequestration and storage, cultural practices, recreation, primary production, and nutrient cycling, among others (MEA 2005). This section summarizes some of the primary climate-driven changes and impacts observed to date and projected to occur in marine and coastal regions of the United States. Changes considered include air and ocean temperatures, precipitation patterns and coastal storms, ocean circulation, sea levels, and ocean chemistry (e.g., pH, dissolved oxygen, salinity), and associated secondary impacts on marine and coastal systems, including species, habitats, ecosystem services, and human communities. The following tables summarize observed and projected future climatic changes, effects on marine and coastal systems, and geographic examples.

Table Directory:

 


Table 1. Changes in air and ocean temperatures, effects on marine and coastal systems, and geographic examples.

Observed & Projected Changes

Observed

  • Air temperatures have increased by 0.8–1°C (1.4–1.8°F) in the United States relative to the beginning of the 20th century (Hansen et al. 2010; Wuebbles et al. 2017; IPCC 2021).
  • The ocean has absorbed approximately 93% of the added atmospheric heat since the 1950s, increasing global sea surface temperatures by about 0.7°C (1.3°F) (Jewett & Romanou 2017). Since 1980, global sea surface temperatures have increased 0.6°C (1°F) (IPCC 2019).
  • Marine heatwaves, or periods of hotter-than-usual ocean temperatures, have been documented for over a century (Hobday et al. 2018). Since the 1980s, marine heatwaves have doubled in frequency and have become more intense (IPCC 2021). Severe marine heatwaves have been observed along both the Atlantic and Pacific coasts of the United States (Mills et al. 2013; Bond et al. 2015; Di Lorenzo & Mantua 2016).

Projected

  • Air temperatures in the United States are projected to increase between 1.2–5.7°C (2.2–10.3°F) by 2100, depending on the model projections used (IPCC 2021).
  • Ocean temperatures are projected to increase between 1.3–2.7°C (2.3–4.8°F) by 2100 (Jewett & Romanou 2017). The frequency, intensity, and duration of marine heatwaves are likely to increase in a changing climate (Oliver et al. 2019; IPCC 2021).

Effects on Marine & Coastal Systems

Ecosystems

  • Altered species’ migration patterns
  • Community shifts: changes in which species co-occur and in interactions among species (e.g., competition between native and invasive species)
  • Phenological shifts: changes in development, age of sexual maturity, timing of spawning, growth, and survival
  • Increased species’ metabolic rates leading to higher consumption of oxygen and decreases in dissolved oxygen levels
  • Reduction in species resilience due to thermal stress, leading to increased disease outbreaks
  • Increased fitness for some native and non-native species, including insect outbreaks
  • Increased risk of invasive species establishment
  • Increased algal blooms and dead zones
  • Loss of sea ice
  • Increased frequency and severity of coral bleaching events
  • Increased risk of wildfire and drought impacts on species and habitats
  • Shifts in agricultural productivity: longer growing seasons
  • Increased risk of extreme heat events

Ecosystem services

  • Loss of coastal protection from wetlands and coral reefs
  • Loss of or alterations to fisheries as species’ ranges shift (e.g., expanded fishing operations as sea ice melts, changes in gear requirements for new species)
  • Loss of subsistence and culturally-valued species
  • Economic losses
  • Declines in naturally available water supplies

Regional Examples of Observed & Projected Impacts

  • Decreased winter sea ice and thawing permafrost in Alaska due to warmer air and water temperatures have enhanced coastal erosion rates as shorelines become more exposed to waves and storm surges as the ice retreats, damaging or destroying infrastructure (ACIA 2005; AFSC 2012).
  • Melting sea ice will also increase freshwater runoff and could lead to decreased salinity levels. The Gulf of Alaska, for example, has already experienced decreased salinity due to melting sea ice (Royer & Grosch 2006).
  • In New England, warming waters have been blamed for a collapsing cod fishery in the Gulf of Maine, where waters have warmed 99% faster than other areas in the country (Pershing et al. 2015).
  • Increased water temperatures frequently favor the survival of invasive species that may stress native fish populations, such as the Atlantic oyster drill (Urosalpinx cinerea), which competes with Olympia oysters (Ostrea lurida) along the West Coast (Sanford et al. 2014).
  • Melting sea ice is opening new shipping lanes in the Northwest Passage and the Northern Sea Route, placing Alaska at the forefront of new economic opportunities (e.g., fishing, oil and gas) as well as a potential site of conflict between Arctic nations trying to stake territorial claims (Forsyth 2018).
  • Ocean temperatures in the northeast Caribbean increased 0.24°C (0.43°F) per decade (Gould et al. 2018).

 

Table 2. Changes in precipitation and coastal storms, effects on marine and coastal systems, and geographic examples.

Observed & Projected Changes

Observed

  • In the past century, the United States has experienced an overall 4% increase in average annual precipitation (Easterling et al. 2017), including an overall increase in extreme precipitation events over the past three to five decades (Walsh et al. 2014).
  • Heavy precipitation events have increased in frequency and intensity since the 1950s (IPCC 2021).

Projected

  • It is generally expected that winter and spring precipitation will increase in the northern United States (Horton et al. 2014; Easterling et al. 2017), while the southwestern and Caribbean regions will experience drier conditions (Walsh et al. 2014; Easterling et al. 2017; Gould et al. 2018).
  • An increase in the frequency and intensity of extreme precipitation events in the United States is projected (Easterling et al. 2017; IPCC 2021). It is projected that extreme daily precipitation events will increase about 7% for each 1°C of global warming (IPCC 2021).
  • Hurricanes and tropical storms are likely to increase in intensity (e.g., increased strength of tropical storms in the Pacific [Murakami et al. 2013] and the Caribbean, Gulf Coast, and eastern coast of the United States [IPCC 2021]) while overall global projections indicate little to no change or even a decrease in frequency of these storms (Kossin et al. 2017; IPCC 2021).

Effects on Marine & Coastal Systems

Ecosystems

  • Altered reproductive timing and success of salmon and other anadromous and marine species
  • Increased coastal dead zones from increased nutrient-rich runoff
  • Increased coastal erosion
  • Altered water quality from salinity changes and pollution loading from non-point sources
  • Increased nutrient and sediment loads in coastal areas downwind or downriver of fires due to increased wildfire frequency and intensity
  • Increased inundation or degradation of important coastal habitats, such as tidal marshes, mangroves, and shallow coral reefs that fish use for protection, spawning, and rearing of juveniles
  • Escalations in freshwater runoff causing increased water stratification in estuaries and coastal waters, reducing primary productivity rates and nutrient upwelling

Ecosystem services

  • Decreased water supply in drought-prone or snowmelt-dependent areas
  • Damage to coastal property, port, and fishing infrastructure
  • Economic stress on fishermen and boat operators as well as subsistence and traditional fishing communities

Regional Examples of Observed & Projected Impacts

  • Since 1970, there have been observed increases in the intensity, frequency, and duration of North Atlantic hurricanes (Carter et al. 2014; Kossin et al. 2017), and increased tropical storm frequency in the Pacific Ocean since 1966 (Chu 2002).
  • More frequent and intense winter storms have been observed in the coastal Northeast and Northwest (Walsh et al. 2014).
  • In the Southeast, the frequency of extreme precipitation events has increased by 10–25% over past 20 years (Kunkel et al. 2013).
  • Decreased precipitation and higher air temperatures increased wildfire frequency, duration, and the wildfire season in the West (Westerling et al. 2006).
  • Total annual precipitation of the heaviest 1% of events (between 1901–2016) increased by 18% in Southeast United States and up to 38% along the Atlantic Coast (Hayhoe et al. 2018).
  • More frequent and intense storms will increase runoff in the Mid-Atlantic, Southeast United States, and the Gulf of Mexico. The “dead zone” in the Gulf may expand in size due to increased nutrient and pollutant loads being carried in the Mississippi River (Rabalais & Turner 2019).
  • Over the course of one month in 2017, Hurricanes Harvey, Irma, and Maria destroyed several coastal communities in the Gulf Coast and Caribbean, causing between $335–475 billion in damages (Willingham 2017). Hurricane Irma was the strongest ever recorded in the Atlantic Ocean and Hurricane Maria was the strongest storm to hit Puerto Rico in a century (Fritz 2017). After these hurricanes, Puerto Rico and the U.S. Virgin Islands experienced a decrease in population size as families were displaced to the U.S. mainland (Artiga et al. 2018).
  • In 2020, four hurricanes––Laura, Sally, Delta, and Zeta––made landfall in Gulf Coast communities in Louisiana and Alabama. The wind, storm surge, and rainfall impacts from these events were felt across eastern Texas, Mississippi, Georgia, Florida, and Arkansas. The impacts from the hurricanes resulted in 58 deaths and $32.7 billion worth of damages (NOAA NCEI 2021).

 

Table 3. Changes in ocean circulation patterns (e.g., natural climatic variability, upwelling, winds), effects on marine and coastal systems, and geographic examples.

Observed & Projected Changes

Observed

  • Ocean circulation patterns, driven by ocean currents (e.g., Gulf Stream) and thermohaline circulation, are critical to the transport of heat, oxygen, nutrients, and carbon throughout the global oceans. Interannual and interdecadal climatic variability, such as the El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), influence ocean circulation, winds, upwelling patterns, temperatures, and precipitation and storms.
  • There has been an observed increase in the intensity of ENSO events: the 1982–83 and 1997–98 El Niño events were the strongest observed in the past century (Hansen et al. 2006; Cai et al. 2015).
  • From 2001–2014, there was intensification of the Pacific trade wind systems, resulting in increased ocean heat transport and rate of global temperature change (Collins et al. 2019).
  • There is some evidence that the Atlantic Meridional Overturning Circulation (AMOC), which controls circulation patterns in the Atlantic Ocean, has weakened over time (Jewett & Romanou 2017; IPCC 2019).

Projected

  • The frequency and intensity of ENSO events may increase as climate patterns (e.g., increased temperatures, decreased winds) shift (Barange & Perry 2009; Yeh et al. 2009; Collins et al. 2019).
  • Potential intensification of upwelling and stronger coastal winds in the California Current (Brady et al. 2017; Xiu 2018).
  • The formation of North Atlantic Deep Water that drives ocean circulation may weaken and result in greater water column stratification (Rahmstorf 2006).
  • The AMOC is very likely to weaken over the 21st century in response to increased greenhouse gas concentrations and influxes of freshwater from Greenland’s ice sheet, which may affect the ability of the AMOC to absorb heat and carbon dioxide (Schmittner et al. 2005; Cheng et al. 2013; IPCC 2019). The Gulf Stream is also projected to weaken over the 21st century (IPCC 2021).

Effects on Marine & Coastal Systems

Ecosystems

  • Incidents of coral bleaching
  • Altered species distribution and migration patterns
  • Shifts in species composition
  • Population declines from decreased food availability and habitat loss
  • Geographic shifts in water salinity
  • Decreased productivity in coastal upwelling areas
  • Loss of fog-dependent coastal forests
  • Widespread fish kills
  • Changes in timing of phytoplankton and zooplankton production
  • Limited prey availability for fish larvae and fish populations
  • Disruption to the ecological connectivity of coral reef populations, further limiting the ability of corals to recover after bleaching events

Ecosystem services

  • Altered structure and productivity of fisheries
  • Extreme weather-related damage to property and coastal areas
  • Declines in net primary productivity due to increased water column stratification and suppressed vertical mixing
  • Fluctuations in fish stocks Reduced carbon dioxide uptake

Regional Examples of Observed & Projected Impacts

  • Changes in seasonal wind patterns along coasts have delayed and/or decreased upwelling events along the West Coast, decoupling trophic interactions and productivity (Barth et al. 2007).
  • Less frequent, more intense upwelling events have been observed in the California Current System (Sydeman et al. 2014). Changes in upwelling strength and ENSO and PDO cycling have also been shown to affect the timing and composition of fish larvae in this system (Brodeur et al. 2008; Auth et al. 2011), highlighting the potential for increased shifts and variability in fish populations and changes in dominant species driven by changes in ocean circulation.
  • Previous ENSO events have led to large increases in sea surface temperature (2–3°C [3.6–5.4°F]) along the California coast (Sydeman & Thompson 2014).

 

Table 4. Changes in sea levels, effects on marine and coastal systems, and geographic examples.

Observed & Projected Changes

Observed

  • Since 1900, global mean sea levels increased by ~15–25 cm (~5.9–9.8 inches) (IPCC 2021). Since 2006, sea level rise increased by 0.35 cm (0.14 inches) per year (IPCC 2021).

Projected

  • Global sea levels are projected to rise between 0.28–1.01 m (0.92– 3.3 ft) by 2100 and 0.37–1.88 m (0.98–6.2 ft) by 2150, with a potential increase of 2 m (6.6 ft) by 2100 and 5 m (16.4 ft) by 2150 under continued very high greenhouse gas emissions and ice sheet loss in the Antarctic and Greenland (IPCC 2021).
  • Low-lying coastal areas, such as islands in the Pacific and Caribbean, and along the Atlantic and Gulf coasts are acutely vulnerable to sea level rise, particularly cities such as Miami, New Orleans, Charleston, and Virginia Beach (Carter et al. 2014; Marra & Kruk 2017; Runkle et al. 2018).

Effects on Marine & Coastal Systems

Ecosystems

  • Saltwater inundation will stress coastal freshwater species
  • Shifts in species distribution and interactions among species
  • Loss or change in location and distribution of coastal breeding grounds and habitat
  • Altered oceanic current patterns and rates
  • Inundation of coastal ecosystems including wetlands and barrier islands
  • Changes (both loss and gain) in habitat availability and types (e.g., marsh migration)
  • Land subsidence and erosion

Ecosystem services

  • Salinization of water supplies
  • Increased economic vulnerability of fisheries-dependent communities
  • Damage to critical infrastructure (e.g., energy systems, utilities, ports)
  • Declines in aquaculture
  • Loss of tribal cultural and archaeological sites
  • Loss of public access to coastlines

Regional Examples of Observed & Projected Impacts

  • Observed rates of sea level rise vary throughout the country based on topography and land subsidence and uplift (Walsh et al. 2014). For example, the rate of sea level rise in the Northeast Atlantic has been higher than global rates in the past few decades (Sweet et al. 2017), leading to greater coastal flooding (Horton et al. 2014).
  • Coastal freshwater forests in the Southeast and in the Gulf of Mexico are undergoing dieback from increasing saltwater intrusion as sea level rises and regional lands subside; in some areas, mangroves are expanding landward (Doyle et al. 2010).
  • Some areas may be experiencing faster rates of sea level rise due to land subsidence (Mitchum 2011). For example, Louisiana is experiencing relative sea level rise of ~0.9 cm (0.37 inches) per year (Ingram et al. 2013) and over 1,880 mi2 (~4,869 km2 ) of wetlands have been inundated since 1930 (Carter et al. 2014). Land subsidence driven by groundwater withdrawals has caused the Chesapeake Bay region to experience the highest rate of sea level rise along the Atlantic Coast over the last few decades (Eggleston & Pope 2013).
  • Forced migration of entire coastal communities, such as the Native Villages of Shishmaref, Kivalina, Shaktoolik, and Newtok on the west coast of Alaska, because of increased erosion as a result of sea ice cover and its buffering effects against storms and high energy waves (ACIA 2005).
  • In Humboldt Bay, California, over 50 cultural sites of importance (e.g., ceremonial and gathering areas) to the native Wiyot Tribe are vulnerable to inundation from sea level rise (Laird 2018).
  • A 3.2-foot rise in sea levels would likely damage over 550 cultural sites and 25,000 acres of coastal land, and displace nearly 20,000 residents in the Hawaiian Islands (Hawai‘i Climate Change Mitigation & Adaptation Commission 2017).

 

Table 5. Changes in ocean chemistry (e.g., pH, salinity, dissolved oxygen), effects on marine and coastal systems, and geographic examples.

Observed & Projected Changes

Observed

  • Since the 1980s, ocean surface pH has declined by 0.017–0.027 pH units per decade (IPCC 2019).
  • Ocean salinity is influenced by freshwater input from precipitation, ice meltwater, and rivers (Boyer et al. 2007; Cazenave & Llovel 2010). Global ocean surface salinity increased 5.3% from 1950–2010 (Jewett & Romanou 2017). Salinity levels in the western North Atlantic have increased slightly since 1967 and held relatively steady in the Gulf of Mexico and Caribbean Sea (Boyer et al. 2007), and decreased in the Gulf of Alaska due to melting sea ice (Royer & Grosch 2006).
  • The oxygen content of ocean waters is influenced by circulation and precipitation patterns that can intensify water stratification and reduce vertical mixing. It is estimated that between 1970–2010 that 0.5–3.3% of oxygen was lost from the ocean surface to 1,000m (~3,281 ft) (Bindoff et al. 2019). Over the last 50 years, oxygen declines have been observed in inland seas, estuaries, and coastal waters (Jewett & Romanou 2017). The Gulf of Mexico and the South Atlantic regions have the largest percentage of water bodies with hypoxic zones in the United States (51% and 55% in the 2000s) (CENR 2010).

Projected

  • Ocean surface water pH may decrease an additional 0.3–0.4 pH units by 2100 (Orr et al. 2005; Feely et al. 2009; Feely et al. 2012; Bopp et al. 2013).
  • Salinity levels may decline due to large freshwater inputs from melting sea ice as temperatures rise (Burkett & Davidson 2012). It is projected that the Pacific Ocean may freshen and the Atlantic may get saltier over the 21st century (IPCC 2021).
  • Dissolved oxygen in oceans could decrease by 3.2–3.7% by 2100 (IPCC 2019). Higher decreases are expected in some regions; for example, the North Pacific may experience an up to 17% decrease under the highest emissions scenario (Jewett & Romanou 2017).

Effects on Marine & Coastal Systems

Ecosystems

  • Decreased reproductive and recruitment success
  • Shifts in species composition and distribution Changes in development, age of sexual maturity, timing of spawning, growth, and survival
  • Altered prey availability (plankton)
  • Changes in shell or skeleton growth rates and morphology
  • Declines of pteropods – the basis of the marine food chain
  • Decrease rates of coral reef formation
  • Cascading trophic shifts
  • Increased risk of invasive species establishment
  • Reduced habitat complexity (increased erosion / decreased growth/ recruitment)
  • Increased algal blooms
  • Increased dead zones
  • Limited availability of preferred prey
  • Shoaling (or shallowing) of the calcium carbonate saturation depth, serving to decrease the area in the water column where it is energetically favorable to form calcium carbonate structures

Ecosystem services

  • Loss of coral reefs and supported fisheries (e.g., oyster hatcheries)
  • Declines in fish populations and fishery productivity
  • Decreased water quality
  • Increased vulnerability of coastal communities and infrastructure

Regional Examples of Observed & Projected Impacts

  • Increased regional ocean acidification has been observed in the North Pacific due to seasonal upwelling of deep CO2-rich waters (Feely et al. 2002).
  • Changes in estuarine and ocean salinity have been observed due to higher freshwater inputs from melting ice and increased precipitation in Alaska (Harris et al. 2017).
  • The northern Gulf of Mexico hypoxic zone, caused by decreased DO concentrations, is the second largest in the world (Griffis & Howard 2013), and can extend up to 23,000 km2 during the summer (Rabalais & Turner 2019).
  • Increases in salinity have caused the salinization of drinking water supplies; for example, the City of Hallandale Beach in Florida had to abandon six of their eight drinking water wells (Berry et al. 2011).
  • West Coast aquaculture operators have experienced lower productivity and higher mortality rates due to ocean acidification and hypoxia (Barton et al. 2012; WA State Blue Ribbon Panel on Ocean Acidification 2012).
  • Certain regions, such as the coastal waters of Alaska and along the West Coast, will experience stronger acidification impacts due to cold waters with relatively high levels of CO2 (Feely et al. 2012; Walsh et al. 2014).
  • In tropical coral reef regions, such as the Pacific Islands and the Caribbean, acidification will limit reef formation and further exacerbate degradation from bleaching events (NRC 2010; IWG 2014).

Table 1. Najjar et al. 2000; Ning et al. 2003; Roessig et al. 2004; Brander 2007; ISAB 2007; O’Connor et al. 2007; Brodeur et al. 2008; Daw et al. 2009; Beamish et al. 2010; Cazenave & Llovel 2010; Link et al. 2010; Najjar et al. 2010; Guidry & Mackenzie 2011; Johnson 2012; Pinsky & Fogarty 2012; Mills et al. 2013; Doney et al. 2014; Leong et al. 2014; Sanford et al. 2014; Sydeman & Thompson 2014; Gould et al. 2015; Hare et al. 2016; IPCC 2019; Yang et al. 2019; IPCC 2021

Table 2. Twilley et al. 2001; Kennedy et al. 2002; Roessig et al. 2004; Daw et al. 2009; Najjar et al. 2010; Berry et al. 2011; Anderson et al. 2013; Needham et al. 2012; Carter et al. 2014; Gould et al. 2015; Grecni et al. 2021

Table 3. Glynn et al. 2001; Behrenfeld et al. 2006; Lehodey et al. 2006; ISAB 2007; Brodeur et al. 2008; Schindler et al. 2008; McIlgorm et al. 2010; Rabalais et al. 2010; Keener et al. 2012; Auth et al. 2011; Glynn et al. 2014; Reynolds et al. 2014; Sydeman & Thompson 2014; Grecni et al. 2021

Table 4. Twilley et al. 2001; Ning et al. 2003; Daw et al. 2009; Najjar et al. 2010; Anderson et al. 2013; Gould et al. 2015; Laird 2018; Grecni et al. 2021

Table 5. Wannamaker & Rice 2000; Cooley & Doney 2009; Doney et al. 2009; CENR 2010; Kelly et al. 2011; Barton et al. 2012; Feely et al. 2012; Johnson 2012; Keener et al. 2012; WA State Blue Ribbon Panel on Ocean Acidification 2012; Griffis & Howard 2013; Kroeker et al. 2013; Mora et al. 2013; Chapin et al. 2014; Doney et al. 2014; IWG 2014; Leong et al. 2014; Wijgerde et al. 2014; Grecni et al. 2021