Effects of climate change on oceans

All this can lead to changes of ocean currents, for example a weakening of the Atlantic meridional overturning circulation (AMOC).

[4] The source for this excess CO2 is clearly established as human-driven, reflecting a mix of fossil fuel burning, industrial, and land-use/land-change emissions.

[4] Several pieces of evidence point to the ocean absorbing roughly a quarter of total anthropogenic CO2 emissions.

The latest key findings about the observed changes and impacts from 2019 include:It is virtually certain that the global ocean has warmed unabated since 1970 and has taken up more than 90% of the excess heat in the climate system [...].

Marine calcifying organisms, such as mollusks and corals, are especially vulnerable because they rely on calcium carbonate to build shells and skeletons.

These include ocean currents and upwelling zones, proximity to large continental rivers, sea ice coverage, and atmospheric exchange with nitrogen and sulfur from fossil fuel burning and agriculture.

The stratified layers limit how much vertical water mixing takes place, reducing the exchange of heat, carbon, oxygen and particles between the upper ocean and the interior.

[2] Satellite image analysis reveals that the oceans have been gradually turning green from blue as climate breakdown continues.

[60][14]: 1310 Human-induced climate change "continues to warm the oceans which provide the memory of past accumulated effects".

In turn, this "invigorates tropical cyclones to make them more intense, bigger, longer lasting and greatly increases their flooding rains".

[61] Climate change affects tropical cyclones in a variety of ways: an intensification of rainfall and wind speed, an increase in the frequency of very intense storms and a poleward extension of where the cyclones reach maximum intensity are among the consequences of human-induced climate change.

Thermohaline circulation is responsible for bringing up cold, nutrient-rich water from the depths of the ocean, a process known as upwelling.

[7][70] The long term observation records show a clear trend: the global salinity patterns are amplifying in this period.

After the plants grow, bacterial decomposition of the organic matter formed by photosynthesis in the ocean consumes oxygen and releases carbon dioxide.

[14][failed verification] In the Indian Ocean for example, productivity is estimated to have declined over the past sixty years due to climate warming and is projected to continue.

[5]: 452  The reduction in ocean productivity is due to the "combined effects of warming, stratification, light, nutrients and predation".

[81][82]: 413  Increasing ocean acidification makes it more difficult for shell-accreting organisms to access carbonate ions, essential for the production of their hard exoskeletal shell.

[84][85] Although the drivers of harmful algal blooms (HABs) are poorly understood, they appear to have increased in range and frequency in coastal areas since the 1980s.

[2]: 16  The parameters that affect the formation of HABs are ocean warming, marine heatwaves, oxygen loss, eutrophication and water pollution.

[91] Coral reefs are important centres of biodiversity and vital to millions of people who rely on them for coastal protection, food and for sustaining tourism in many regions.

The IPCC Sixth Assessment Report in 2022 found that: "Since the early 1980s, the frequency and severity of mass coral bleaching events have increased sharply worldwide".

[90]: 381  It is expected that many coral reefs will suffer irreversible changes and loss due to marine heatwaves with global temperatures increasing by more than 1.5 °C.

[106] Increased risks of floods, diseases, parasites and harmful algal blooms are climate change impacts on aquaculture which can lead to losses of production and infrastructure.

[105] Some effects on marine mammals, especially those in the Arctic, are very direct such as loss of habitat, temperature stress, and exposure to severe weather.

Furthermore, if a species is unable to successfully migrate to a suitable environment, it will be at risk of extinction if it cannot adapt to rising temperatures of the ocean.

The loss of sea ice habitat will reduce the abundance of seal prey for marine mammals, particularly polar bears.

[117] Sea ice changes may also have indirect effects on animal health due to changes in the transmission of pathogens, impacts on animals' body condition due to shifts in the prey-based food web, and increased exposure to toxicants as a result of increased human habitation in the Arctic habitat.

For example: In the Mediterranean, increased sea surface temperatures, salinity, upwelling intensity, and sea levels have led to a reduction in prey resources, causing a steep decline in the short-beaked common dolphin subpopulation in the Mediterranean, which was classified as endangered in 2003.

[127] At the Shark Bay World Heritage Area in Western Australia, the local population of the Indo-Pacific bottlenose dolphin had a significant decline following a marine heatwave in 2011.

[134][135] Documented effects in the scientific literature include impacts on reproduction, range, prey access, interactions with human activities, and individual health condition.

Overview of climatic changes and their effects on the ocean. Regional effects are displayed in italics. [ 1 ]
This NASA animation conveys Earth's oceanic processes as a driving force among Earth's interrelated systems.
Most excess heat trapped by human-induced global warming is absorbed by the oceans, penetrating to its deeper layers. [ 9 ]
Energy (heat) added to various parts of the climate system due to global warming (data from 2007).
Land surface temperatures have increased faster than ocean temperatures as the ocean absorbs about 92% of excess heat generated by climate change. [ 10 ] Chart with data from NASA [ 11 ] showing how land and sea surface air temperatures have changed vs a pre-industrial baseline.
The illustration of temperature changes from 1960 to 2019 across each ocean starting at the Southern Ocean around Antarctica. [ 12 ]
Ocean acidification: mean seawater pH. Mean seawater pH is shown based on in-situ measurements of pH from the Aloha station . [ 30 ]
Change in pH since the beginning of the industrial revolution. RCP2.6 scenario is "low CO 2 emissions". RCP8.5 scenario is "high CO 2 emissions". [ 31 ]
The global average sea level has risen about 250 millimetres (9.8 in) since 1880, [ 42 ] increasing the elevation on top of which other types of flooding ( high-tide flooding , storm surge ) occur.
Waves on an ocean coast
Drivers of hypoxia and ocean acidification intensification in upwelling shelf systems. Equatorward winds drive the upwelling of low dissolved oxygen (DO), high nutrient, and high dissolved inorganic carbon (DIC) water from above the oxygen minimum zone . Cross-shelf gradients in productivity and bottom water residence times drive the strength of DO (DIC) decrease (increase) as water transits across a productive continental shelf . [ 52 ] [ 53 ]
Global map of low and declining oxygen levels in the open ocean and coastal waters. The map indicates coastal sites where anthropogenic nutrients have resulted in oxygen declines to less than 2 mg L –1 (red dots), as well as ocean oxygen minimum zones at 300 metres (blue shaded regions). [ 55 ]
Decline in arctic sea ice extent (area) from 1979 to 2022
Examples of projected impacts and vulnerabilities for fisheries associated with climate change
Bleached Staghorn coral in the Great Barrier Reef .
A polar bear waiting in the Fall for the sea ice to form.
Harp seal mother nursing pup on sea ice