Climate Change
Impacts Across the System

We are already seeing the impacts of climate change in national marine sanctuaries and surrounding communities. The worsening, complex, and interrelated impacts of climate change are reshaping the status quo in treasured, and depended on, marine and coastal areas. This page discusses some of the common and pressing climate change challenges facing the National Marine Sanctuary System.

To read about the specific climate impacts in each sanctuary, review the sanctuary climate change impact profiles. For more information on climate science, visit climate.gov.

Ocean and Lake Warming

Three photos showing flooding, a hurricane, and coral bleaching.
Impacts from climate change that are exacerbated by warming ocean and lake waters can include (left to right) sea level rise and flooding as shown in Port Arthur, Texas after Hurricane Harvey; more powerful hurricanes including the Category 4 Hurricane Michael that struck the Florida panhandle; and coral bleaching as seen here in National Marine Sanctuary of American Samoa. Photos: D.J. Martinez and NOAA

The majority of heat trapped in the atmosphere by greenhouse emissions is absorbed in the ocean. As a result, the ocean has warmed in recent decades. Today's sea surface temperatures are the highest ever recorded. Climate change is also rapidly warming lakes, directly impacting resources and driving evaporation. In the Great Lakes, lake warming is changing the timing of the seasonal mixing of nutrients from the lake floor into the water column. Global ocean and lake warming has direct impacts on species, as well as knock-on effects by driving other climate change impacts like sea level rise, ocean deoxygenation, increasing storm strength, and more.

Considerations for sanctuaries include:

  • A warming ocean, warming lakes, and marine heatwaves, directly pressure marine species, impacting their ability to survive and reproduce, and often causing them to shift their range. These changes have cascading effects on marine ecosystems, impacting resources vital to coastal communities and economies.
  • Ocean warming undermines coral reef health by driving coral bleaching events and leading to increased incidences of infectious disease. Climate change is already damaging reef systems protected by sanctuaries.
  • Ocean warming, by melting ice sheets and glaciers and leading to the thermal expansion of seawater, is driving sea level rise, which poses a range of dangers to ecosystems and communities (discussed below).
  • Ocean and lake warming is thought to intensify harmful algal blooms, and in doing so, pose a threat to the people and creatures that use the impacted areas in the ocean, lake, and sanctuary.

Sea Level Rise and Changes in Lake Levels

A light green house sits at the end of a flooded road, you can see driveways and trash bins sitting in water off the side of the road.
Sea level rise is making low-lying coastal areas like Tybee Island, Georgia, more vulnerable to frequent and widespread flooding. Since 1935, as measured by a local NOAA tide gauge, this beach community has experienced 10 inches of sea level rise. Sanctuaries help educate local communities about climate science and protect ecosystems that mitigate the effects of flooding. Photo: J. Evans

Sea levels are rising as warmer temperatures melt ice sheets and glaciers, and ocean warming drives thermal expansion of seawater. Seawater is increasingly flooding low-lying land, submerging coastal habitats, facilities, and roads, and contaminating coastal sources of freshwater and freshwater habitats. Further, climate change’s impact on evaporation and precipitation can lead to fluctuations in lake levels. While the degree of lake level change that will be seen in the Great Lakes as a result of climate change is uncertain, resources may face increased exposure and flooding as a result of climate change.

Considerations for sanctuaries include:

  • Sea level rise increases the risk of damage to homes and buildings, including sanctuary facilities, from waves, tides, and storm surges, such as those that accompany hurricanes.
  • Changing water levels periodically erode and degrade coastal archaeological sites, reducing their scientific value.
  • Rising sea levels are encroaching upon shorelines, narrowing beaches, increasing erosion, and affecting coastal ecosystems in our national marine sanctuaries, including nesting habitat for seabirds and marine mammal haul-out sites.
  • Rising sea and lake levels may damage docks, boat houses, and other coastal structures, as well as those owned and operated by individuals and companies that use sanctuary resources (e.g., fishermen, whale watch companies, divers). Fluctuations in Great Lakes level, resulting from climate change’s impact on the availability of water and weather events, can damage and increase the exposure of sanctuary heritage sites.
  • Coastal flooding from rising sea levels mobilizes pollutants and fertilizers that drain into the ocean, creating harmful algal blooms and ocean dead zones.

Changes in Weather and Climate

Four tropical weather systems are swirling above dark blue water and dark green land.
Rising ocean and air temperatures provide fuel for more powerful hurricanes. These tropical weather systems were observed with the GOES-16 satellite on September 9, 2018 over the northwest Atlantic Ocean. Shown (right to left) are Tropical Storm Helene, Tropical Depression Nine, Hurricane Florence, and an unnamed low pressure system over the Florida peninsula. Photo: NOAA

Covering 70 percent of Earth’s surface, the ocean exerts major control on climate and weather by dominating Earth’s energy and water cycles. It absorbs vast amounts of solar energy. Heat and water vapor are redistributed globally through ocean currents and atmospheric circulation. Changes in ocean circulation can lead to significant and even abrupt changes in climate and weather, both locally and on a global scale. Climate change-driven warming is leading to ocean warming, impacting weather patterns and influencing extreme weather events. Ocean warming is also melting polar ice and causing an influx of freshwater that further influences currents and the movement of water.

Considerations for sanctuaries include:

  • The increased likelihood and intensity of some extreme weather events, as a result of climate change, impacts national marine sanctuary habitats, coastal infrastructure, and communities.
  • West Coast sanctuaries depend on upwelling, an oceanographic process that brings deep water to the surface, to provide an influx of nutrients into their ecosystems. Changes in upwelling regimes have large biological effects on national marine sanctuaries along the West Coast of the United States. Persistently warmer sea surface temperatures could lead to long-term changes in the magnitude and timing of ocean upwelling.
  • Many communities rely on an intimate understanding of coastal processes for their livelihoods, with seasonal activities shaping everyday life. Changing weather and seasons not only alter or prevent seasonal activities, they diminish the value of shared traditions and heritage.
  • Climate change’s impact on atmospheric circulation, ocean currents, and the water cycle, results in changes to weather and oceanographic processes that impact marine and coastal ecosystems. For example, isolated islands, like the Samoan islands, depend on currents to transport coral larvae, but as climate change leads to weakening currents that vital contributor to coral reefs may become less reliable.
  • In the Gulf of Maine, home to Stellwagen Bank National Marine Sanctuary, the ocean is warming rapidly as the global trend in ocean warming is compounded by the warming effects of changes in the region’s defining currents. Warming from climate change has caused an influx of fresh water from melting ice that has changed ocean circulation patterns in the region and brought warmer water to the area.


Ocean and Lake Acidification

Two fishers in orange waders stand on a boat and sort their clam catch.
A recent study suggests that future ocean acidification conditions may result in long-term decline of the $500 million annual Atlantic sea scallop fishery, despite increased management. Photo: NOAA
As humans emit carbon dioxide into the atmosphere, the ocean and lakes absorb much of those emissions. In fact, since the 1700s, the ocean has absorbed about a third of all human carbon dioxide emissions. However, absorbing all this carbon dioxide changes the chemistry of the ocean, this process is called ocean acidification. This has the potential to fundamentally change marine ecosystems, food webs, and habitats globally, including national marine sanctuaries.
Learn more about ocean acidification and NOAA’s work to understand and address it.

Considerations for sanctuaries include:

  • Ocean acidification prevents some plants and animals at the base of the food web, as well as many larger organisms like shellfish and corals, from building and maintaining the protective skeletons or shells they need to survive. This can impact whole sanctuary ecosystems.
  • Ocean acidification can also affect the growth, reproduction, and larval success of species, having cascading effects through food webs.
  • The upwelling regime that West Coast sanctuaries depend on is also leading to rapid ocean acidification in the region, since the deep waters brought up through upwelling are already more acidic than surface waters. This rate of ocean acidification is impacting key sanctuary species, such as the shellfish and fish that coastal communities rely on for both subsistence and commercial harvest.
  • Acidification in the Great Lakes sanctuaries is determined in part by the watersheds of the lakes, but as a result of carbon dioxide emissions the lakes are expected to see increased acidification. This acidification can threaten sanctuary resources such as iron and steel-hulled shipwrecks.

Ocean Deoxygenation

A Humboldt squid swims through dark water.
In Cordell Bank National Marine Sanctuary, deoxygenation can lead to an increase in the presence of certain species that thrive in low oxygen conditions, such as Humboldt squid. This shift could have economic impacts, as Humboldt squid prey on economically important species for the area. Photo: Rick Starr/NOAA

As climate change causes water in the ocean and lakes to warm, the ability of that water to hold oxygen declines, reducing the total amount of oxygen in the ocean and the amount of oxygen that is transferred from the surface down the water column. This process is called deoxygenation, and it is one significant impact of greenhouse gas emissions. Deoxygenation can contribute to low oxygen conditions, called hypoxia. Hypoxic areas in the ocean and lakes stress organisms and cause mortality events for species in the area.

Considerations for sanctuaries include:

  • Deoxygenation can impact species’ ability to survive and thrive, and it can compound other human causes of hypoxia (such as nutrient pollution). This can lead to mortality events and drive species to move, disrupting the food web in sanctuaries.
  • Deoxygenation is a particular concern for West Coast sanctuaries. The upwelling processes that are important for ecosystems in West Coast sanctuaries brings lower oxygen water to the surface and the impacts of this influx of lower oxygen water is amplified by deoxygenation.
  • Ocean deoxygenation compounds the other ocean chemistry challenges facing species, such as ocean acidification (discussed previously), creating cumulative climate stress across sanctuaries.

Changes in Species Movements and Behavior

Saltmarsh on the left and parrotfish on the right.
Black mangrove trees encroaching into a saltmarsh cordgrass wetland near the northern edge of mangrove range limits, Guana Tolomato Matanzas National Estuarine Research Reserve, Florida. Photo: J. Parker. Right: Tropicalization of seagrass meadows is occurring in the northern Gulf of Mexico, where species such as this stoplight parrotfish (typically associated with coral reefs) can now be observed that were absent from surveys in the 1970's. Photo: Adona9

Globally, species are on the move due to climate impacts. In the ocean, many species are moving toward the poles or into deeper water. In the Northeast Atlantic, for example, species have moved north and into deeper waters seeking preferred temperatures. Climate change is also impacting other aspects of species’ behavior, including shifting the timing of migration and reproduction. These changes have significant impacts on ecosystems and food webs, and occur alongside other climate stressors, like acidification and deoxygenation, and climate change-driven mortality events.

Considerations for sanctuaries include:

  • Changes in the movement of species mean that some species with economic and cultural significance to sanctuary users are no longer present within sanctuaries in the same volume, with the same consistency, or at the same time as they may have been previously.
  • Changes in species’ behavior to adapt to climate change impacts can also expose them to different or additional climate change stressors. For example, as salmon in Washington adapt their migration patterns to avoid warming streams, they are at greater risk of being impacted by limited food availability or changes in food availability related to climate change.
  • While climate change impacts may encourage species to leave certain areas, they can also make those areas more hospitable to invasive species. For sanctuaries already dealing with an incursion of invasive species, climate change can increase their competitive advantage against native species.