Ocean and Lake Warming
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
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
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
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
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
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.