Basic:
Oceans
Although the world's oceans may appear virtually limitless, the rapid and unprecedented rise in
atmospheric CO2 levels since the Industrial Revolution are pushing these vast bodies of water to
their physiological limits. The burning of fossil fuels, deforestation, and other human-activities
that contribute to climate change dramatically alter Earth's oceans, and these changes will
continue to intensify. Oceans cover two-thirds of the world's surface area and support the
greatest diversity of life on Earth. Coastal and island tribal communities rely on oceans and
marine wildlife for subsistence and ceremonies, yet these tribes are also at the highest risk for
storm surges, sea level rise, and erosion, and are often on the forefront of battling climate
change.
Warming oceans
According to the Intergovernmental Panel on Climate Change (IPCC), the same forces that
contribute to surface temperature increases are likewise warming the oceans. Over the past
100 years, the average global sea surface temperature has increased by approximately 0.13° C
per decade.1 This change represents an average across the entire ocean, so both regional and
temporal variations exist. For example, the IPCC has concluded that the Atlantic Ocean
accounts for the most significant change, as warmer ocean temperatures lead to more intense
tropical storms and hurricanes. Oceanic temperature extremes are increasing as well, such as
marine heat waves (MHWs). MWHs are drastic increases in the ocean’s temperature that are
relatively short-lived and are highly localized.2 MHWs can negatively impact marine wildlife,
and in turn, marine birds that consume fish and other sea creatures. MHWs are a relatively new
phenomenon and the causes and impacts they carry are still being understood.
One major and alarming consequence of ocean warming is clear. Coral reefs are dying all over
the world, in a process known as "coral bleaching." Corals are tiny animals that live in immense
colonies and harvest nutrients from a particular type of algae that inhabits their cells. Together,
coral and algae create limestone reefs that provide habitat and food for a vast array of life; they
make up one of the most productive ecosystems on Earth. The symbiotic relationship between
coral and algae, however, is highly sensitive to temperature fluctuations. If temperatures rise
above the coral's physiological thresholds, the algae die, leaving the coral without color or its
source of nutrients. Corals can recover from short-term bleaching, but extended bleaching
ultimately leads to mortality. In 2021, when the warmest ocean temperatures on record were
measured, the oceans also experienced a massive coral die-off.3 Dead coral reefs will take
decades or even centuries to recover, if they can recover. Dying coral communities are
accompanied by losses in marine biodiversity, shoreline protection, fisheries, and medicinal
products. Native cultures and peoples in Hawai`i are threatened by the loss of coral reefs, as
they rely on the reef for their traditions and food systems, and the health of coral reefs reflects
the overall health of the surrounding ocean.4
Coastal dead zones
In addition to the fisheries lost as an impact of coral bleaching, fisheries are disappearing in
other regions due to an increase in ocean "dead zones," another phenomenon linked to climate
change. Earth is experiencing more intense winds, which cause an upwelling in nutrient-rich
waters from the deep sea. When this nutrient-rich water reaches the sunlight, ocean plants
known as phytoplankton bloom in great numbers. These tiny plants exist at the bottom of the
food chain and provide food for small fish and shellfish. Yet when more phytoplankton bloom
than fish can consume, they die and drift to the ocean floor, where bacteria decompose them.
The process of decomposition causes hypoxia, or oxygen depletion in the water.5 Fish and
shellfish that cannot escape hypoxic water suffocate from lack of oxygen and die. While ocean
dead zones have been documented since at least the mid-nineteenth century, studies suggest
their frequency and duration are increasing, and new regions are experiencing the phenomena.
The largest dead zones are off the Gulf of California and the coast of Peru, areas once
renowned for their fisheries.6 Former fishers in these regions are now struggling to keep their
businesses running and have had to turn to other work, some of whom have been upholding
traditional fishing methods for millennia.
Ocean acidification
In addition to raising ocean water temperatures, global warming is also causing the rapid and
unprecedented acidification of Earth's oceans. Between 30 and 50 percent of the carbon
emitted from the burning of fossil fuels and other anthropogenic activities over the last 200
years now resides in our oceans.7 This massive carbon influx has not occurred without
consequences. When carbon dioxide is taken up by seawater, carbonic acid is formed. Some of
this carbonic acid is neutralized by other components of seawater; however, the overall effect
is acidification. Since the Industrial Revolution in the eighteenth century, the pH of surface
seawater has decreased 0.1 units, equivalent to a 30 percent increase in hydrogen ions.8 This
change represents a considerable acidification of the oceans and decreases seawater's
subsequent ability to absorb more carbon in the future. Ocean acidification will adversely affect
the process of calcification, the process by which animals such as corals and mollusks form
plates and shells from calcium carbonate. Because such creatures are near the bottom of the
food chain, their survival is fundamental to the overall health of Earth's oceans. This will also
disrupt a primary human food source, leading to famine and potential malnutrition in certain
parts of the world.9
Marine wildlife in the Pacific Northwest is already being impacted by ocean acidification, and
Tribes who rely on this wildlife for subsistence and cultural purposes are subsequently being
affected. The Swinomish Tribe in Washington rely on clams, oysters, and salmon for their food
systems, which are all species that are negatively impacted by ocean acidification. As Olympia
oyster populations decline due to ocean acidification, overcrowding, and competition from
Pacific oysters, the Swinomish have relocated some Olympia oysters to beaches with less
competition, and where ocean pH can be better monitored.10 The Swinomish are also
constructing modern clam gardens, which replicate clam harvesting practices their ancestors
utilized for millennia. These clam gardens have the potential to stabilize clam populations for
the Swinomish to harvest, even as wild populations decline. They are hopeful that results from
the clam garden can be replicated for nearby salmon populations.
The world's oceans are its most important storehouses of CO2, sequestering an estimated total
of 38,000 gigatons (one billion metric tons) of the greenhouse gas.11 This natural capacity is
truly extraordinary, especially given that the atmosphere and landmass combined sequester
approximately 300 gigatons. Geoengineers are examining the potential of the oceans to
sequester additional CO2 from the atmosphere, which may provide a solution to warming global
temperatures, but carries the potential to increase the acidity of the ocean. Geoengineering is
highly controversial as it may have unintended consequences that are ultimately more
detrimental than beneficial. Ocean-based carbon-removal strategies include fertilizing the
ocean to boost the growth of photosynthetic organisms that sequester CO2; changing the
chemistry of seawater to absorb more greenhouse gases; and sending electrical currents
through the water to break apart molecules and increase the ability of CO2 sequestration.12 The
impacts of this on ocean life and the overall chemistry of the ocean are currently unknown.
Other geoengineering approaches to the ocean have been proposed and countless others are
being researched.
While geoengineering could aid in achieving net zero carbon emissions, there are natural
solutions which could achieve the same result, such as any projects that mitigate and sequester
carbon. For more information on one such example, see ITEP’s Forests Basic Information Page.
These natural solutions should be held with the same value and consideration as
geoengineering.
Sea level rise
One of the most widely known and well-documented consequences of a shifting climate is sealevel rise —
an impact already apparent in many Alaskan coastal villages. Sea-level rise is the
result of thermal expansion (water expands as it warms) and the loss of land-based ice,
including glaciers and permafrost, as temperatures rise. The global mean sea level has risen
between 8 and 9 inches since the beginning of the Industrial Revolution.13 This rate is not
uniform across all regions; in fact, sea levels are projected to decline in some regions. For
example, the U.S. Environmental Protection Agency (USEPA) reports that Atlantic Coastal water
rose five to six inches above the global average.14 Alaska, too, is experiencing dramatic land
loss. Higher seas erode shorelines; cause saltwater encroachment into inland water sources,
including aquifers and creeks; and result in more frequent flooding. The IPCC suggests that
rising sea levels could convert roughly one third of Earth's wetlands to open water-destroying a
key ecosystem for many plant and animal species, along with nutrient uptake and water
filtration capacity.15 Scientists suggest that storm surges will become more severe as the
climate changes. This impact will be exacerbated by the eroded shorelines.
Changes in the world's oceans will have serious and likely devastating effects on low-lying
coastal communities around the world. The plight of Native Alaskans of the tiny communities of
Newtok and Kivalina has garnered worldwide attention. Yet the residents of Newtok, Kivalina,
and other Alaskan Native villages are certainly not the only people at risk of the effects of
climate change. The Florida coasts are renowned for their extensive, gently sloping beaches
that create wide expanses of white sand. Yet models predict that sea levels could rise 8 to 30
inches in the region, which would result in a shoreline loss of hundreds of feet. This
encroachment would extend beyond the beach and have severe effects for the region's tourism
and agricultural industries.
Further, saltwater encroachment into low-lying areas would likely seep into underground
aquifers and contaminate water used for municipal, commercial, and agricultural uses. Both the
Hollywood and Big Cypress reservations of the Seminole Tribe, as well as Miccosukee Tribal
lands, are located in the Everglades region, where land elevation averages about one foot
above sea level. This region is likely to be affected by rising seas and is at great risk for severe
flooding, both from the rise itself and from intense storm surges. Sea level and weather
changes, as well as saltwater encroachment, also threaten the plants and animals on which
these tribes rely for their traditional lifestyles.
Earth's hydrologic cycle creates a close bond between the sea and freshwater sources. Changes
in the ocean will impact the availability of potable water for tribal communities throughout the
United States. Oceanic impacts will not be confined to coastal areas, though communities along
our coasts will be the first to experience the impacts of these changes. Tribes who rely on
marine mammals, fish, and shellfish for subsistence, and who are most at-risk for severe storm
surges, erosion, and sea-level rise, will be forced to confront some of the most immediate,
severe, and abrupt impacts of Earth's changing climate.