Effects of climate change on oceans

Waves on an ocean coast

Animated map exhibiting the world's oceanic waters. A continuous body of water encircling the Earth, the World Ocean is divided into a number of principal areas with relatively free interchange among them. Five oceanic divisions are usually reckoned: Pacific, Atlantic, Indian, Arctic, and Southern; the last two listed are sometimes consolidated into the first three.

Global mean land-ocean temperature change from 1880–2011, relative to the 1951–1980 mean. The black line is the annual mean and the red line is the 5-year running mean. The green bars show uncertainty estimates. Source: NASA GISS

Energy (heat) added to various parts of the climate system due to global warming.

Global warming can effect sea levels, coastlines, ocean acidification, ocean currents, seawater, sea surface temperatures as well as depths, tides, the sea floor, weather and change entire climates. All of these affect how a society functions.

Sea level

Coasts

Global warming in the last century has increased sea levels worldwide, though there are regional variations; see sea level rise. Although global warming has affected the volume of seawater in all of the world’s oceans, it is important to look at the change in sea level in particular coastal areas, especially throughout short periods of time (fifty to one hundred years). In order to estimate the rise in global seawater level, scientists combine sea level trends at tidal stations around the world.

There are a number of factors affecting rising sea levels, including the thermal expansion of seawater, the melting of glaciers and ice sheets on land, and possibly human changes to groundwater storage. With regards to thermal expansion, the increase in the atmosphere’s greenhouse gas content has a warming effect on the whole planet but especially on the oceans, which absorb much of the heat. Despite water’s high heat capacity, this heat that is radiated into the ocean by greenhouse gases in the atmosphere cause water molecules to expand, thus creating more water volume in the oceans. With concern to melting glaciers and ice sheets, global warming also has an enormous impact. Higher global temperatures melt glaciers such as the one on Greenland, which flow into the oceans, adding to the amount of seawater. A large rise (in the order of several feet) in global sea levels poses many threats. According to the U.S. Environmental Protection Agency (EPA), “such a rise would inundate coastal wetlands and lowlands, erode beaches, increase the risk of flooding, and increase the salinity of estuaries, aquifers, and wetlands.”

The areas which would be most affected by rising sea levels are, of course, coastal regions. The increase in sea level along the coasts of continents, especially North America are much more significant than the global average. According to 2007 estimates by the International Panel on Climate Change (IPCC), “global average sea level will rise between 0.6 and 2 feet (0.18 to 0.59 meters) in the next century. Along the U.S. Mid-Atlantic and Gulf Coasts, however, sea level rose in the last century 5 to 6 inches more than the global average. This is due to the subsiding of coastal lands. The sea level along the U.S. Pacific coast has also increased more than the global average but less than along the Atlantic coast. This can be explained by the varying continental margins along both coasts; the Atlantic type continental margin is characterized by a wide, gently sloping continental shelf, while the Pacific type continental margin incorporates a narrow shelf and slope descending into a deep trench. Since low-sloping coastal regions should retreat faster than higher-sloping regions, the Atlantic coast is more vulnerable to sea level rise than the Pacific coast.

Society

The rise in sea level along coastal regions carries implications for a wide range of habitats and inhabitants. Firstly, rising sea levels will have a serious impact on beaches—a place which humans love to visit recreationally and a prime location for real estate. It is ideal to live on the coast due to a more moderate climate and pleasant scenery, but beachfront property is at risk from eroding land and rising sea levels. Since the threat posed by rising sea levels has become more prominent, property owners and local government have taken measures to prepare for the worst. For example, “Maine has enacted a policy declaring that shorefront buildings will have to be moved to enable beaches and wetlands to migrate inland to higher ground.” Additionally, many coastal states add sand to their beaches to offset shore erosion, and many property owners have elevated their structures in low-lying areas. As well, with the effect of large storms on coastal lands eroding and ruining properties governments have looked into buying land and having residents relocate further inland.

Another important coastal habitat that is threatened by sea level rise is wetlands, which “occur along the margins of estuaries and other shore areas that are protected from the open ocean and include swamps, tidal flats, coastal marshes and bayous.” Wetlands are extremely vulnerable to rising sea levels, since they are within several feet of sea level. The threat posed to wetlands is serious, due to the fact that they are highly productive ecosystems, and they have an enormous impact on the economy of surrounding areas. Wetlands in the U.S. are rapidly disappearing due to an increase in housing, industry, and agriculture, and rising sea levels help contribute to this dangerous trend. As a result from rising sea levels, the outer boundary of wetlands would erode, forming new wetlands more inland. According to the EPA, “the amount of newly created wetlands, however, could be much smaller than the lost area of wetlands— especially in developed areas protected with bulkheads, dikes, and other structures that keep new wetlands from forming inland.” When estimating a sea level rise within the next century of 50 cm (20 inches), the U.S. would lose 38% to 61% of its existing coastal wetlands.

A rise in sea level will have not only a negative impact on coastal property and economy, but it will also diminish our supply of fresh water. According to the EPA, “Rising sea level increases the salinity of both surface water and ground water through salt water intrusion.” Coastal estuaries and aquifers, therefore, are at a high risk of becoming too saline from rising sea levels. With concern to estuaries, an increase in salinity would threaten aquatic animals and plants that cannot tolerate high levels of salinity. Aquifers often serve as a primary water supply to surrounding areas, such as Florida’s Biscayne aquifer, which receives freshwater from the Everglades and then supplies water to the Florida Keys. Rising sea levels would submerge low-lying areas of the Everglades, and salinity would greatly increase in portions of the aquifer. A considerable rise in sea level and decreasing amounts of freshwater along the Atlantic and Gulf coasts, therefore, would make those areas rather uninhabitable.

Global issue

Since rising sea levels present a pressing problem not only to coastal communities but also the whole global population, much scientific research has been performed to analyze the causes and consequences of a rise in sea level. The U.S. Geological Survey conducted such research concerning coastal vulnerability to sea level rise, and it incorporated six physical variables to analyze the changes in sea level. The six variables were the following: geomorphology; coastal slope (percent); rate of relative sea level rise (mm/yr); shoreline erosion and acceleration rates (m/yr); mean tidal range (m); and mean wave height (m). Research was conducted on the different coasts of the U.S., and the results are very useful for future reference. Along the Pacific coast, the most vulnerable areas are low-lying beaches, and “their susceptibility is primarily a function of geomorphology and coastal slope.” With concern to research performed along the Atlantic coast, the most vulnerable areas to sea level rise were found to be along the Mid-Atlantic coast (Maryland to North Carolina) and Northern Florida, since these are “typically high-energy coastlines where the regional coastal slope is low and where the major landform type is a barrier island.” With regards to the Gulf coast, the most vulnerable areas are along the Louisiana-Texas coast. According to the results, “the highest-vulnerability areas are typically lower-lying beach and marsh areas; their susceptibility is primarily a function of geomorphology, coastal slope and rate of relative sea-level rise.”

It is crucial that human awareness about rising sea levels and the consequences of it increases. Humans have a substantial influence on the rise of sea level by emitting more and more carbon dioxide into the atmosphere through automobile use and industry. A higher amount of carbon dioxide in the atmosphere leads to higher global temperatures, which then results in thermal expansion of seawater and melting of glaciers and ice sheets.

Ocean currents

The currents in the world’s oceans are a result of varying temperatures associated with the changing latitudes of our planet. As the atmosphere is warmed most near the equator, the hot air near the surface of our planet is heated, causing it to rise and draw in cooler air to take its place, creating what is known as circulation cells. This ultimately causes the air to be significantly colder near the poles than at the equator.

Driving surface currents is the wind patterns associated with these circulation cells. They end up pushing the surface water to the higher latitudes where the air is now cold. It cools the water down enough, to where it is capable of dissolving more gasses and minerals.This causes it to become very dense in relation to lower latitude waters which in turn causes it to sink to the bottom of the ocean, forming what is known as North Atlantic Deep Water, or NADW, in the north, and Antarctic Bottom Water, or AABW, in the south. By virtue of this sinking, the upwelling that occurs in lower latitudes, and the driving force of the winds on surface water, the ocean currents all act to circulate all water throughout the entire ocean.

When global warming is added into the equation, changes occur, especially in the regions where deep water is formed. With the warming of the oceans and subsequent melting of glaciers and the polar ice caps, more and more fresh water is released into the high latitude regions where deep water is formed. This extra water that gets thrown into the chemical mix dilutes the contents of the water arriving from lower latitudes. This reduces the density of the surface water and as such, the water sinks slower than it normally would.

An important thing to note about ocean currents is that they provide the necessary nutrients for life to sustain itself in the lower latitudes. Should the currents slow down, life would have less nutrients being brought to it to be able to sustain it and the food chain would crumble, irreparably damaging the marine ecosystem. Slower currents would also mean less carbon fixation. Naturally, the ocean is the largest sink within which carbon is stored. When waters become saturated with carbon, the excess carbon will have nowhere to go because the currents are not bringing up enough fresh water to fix the excess. This causes a rise in atmospheric carbon which in turn causes positive feedback that can lead to a runaway greenhouse effect.

Ocean acidification

Global warming's additional effect on the carbon cycle is ocean acidification. The ocean and the atmosphere constantly try to maintain a state of equilibrium. So a rise in atmospheric carbon naturally leads to a rise in oceanic carbon. When carbon is dissolved in water, it forms hydrogen and bicarbonate ions, which in turn breaks down to hydrogen and carbonate ions. All these extra hydrogen ions increase the acidity of the ocean and make it harder for planktonic organisms that depend on calcium carbonate for their shells to survive. A decrease in the base of the food chain will, once again, be destructive to the ecosystems to which they belong. With less of these photosynthetic organisms present at the surface of the ocean, less carbon will be converted to oxygen, thereby letting the greenhouse gasses go unchecked.

Weather

The effects of global warming on weather patterns is also interesting as it pertains to cyclones. Scientists have found that although there have been fewer cyclones than in the past, the intensity of each cyclone has increased. A simplified definition of what global warming means for the planet is that colder regions will get warmer and warmer regions would get much warmer. However, speculation also exists saying that the complete opposite could be true. A warmer earth could serve to moderate temperatures worldwide. Much is still not understood about the earth’s climate because it is very difficult to make climate models. As such, predicting the effects global warming might have on our planet is still an inexact science.

Sea floor

Definition

The contents of the ocean floor vary diversely in their origin from eroded land materials carried into the ocean by rivers or wind flow, the waste and decompositions of sea animals, precipitation of chemicals within the sea water it self, and even some from outer space. There are four basic types of sediment of the seafloor. Terrigenous describes the sediment derived from the materials eroded by rain, rivers, glaciers and that blown into the ocean by the wind such as volcanic ash. Biogenous describes the sediment made up of the hard parts of sea animals that compile on the bottom of the ocean. Hydrogenous sediment is dissolved materials that precipitate in the ocean when conditions in the ocean change. Lastly, Cosmogenous sediment describes extraterrestrial sources. These are the components that make up the seafloor under their genetic classifications.

Terrigenous

Terrigenous sediments is the most abundant sediment found on the seafloor. Followed by the biogenous sediment. In areas of the ocean floor where the sediment is 30% biogenous materials or more, it is then labeled as an ooze. There are two types of oozes: Calcareous oozes and Siliceous oozes. Plankton is the contributor of oozes. Calcareous oozes are predominantly composed of calcium shells found in phytoplankton such as coccolithophores and zooplankton like the foraminiferans. These calcareous oozes are never found past depths deeper than about 4,000 to 5,000 meters because as you go deeper down, the calcium dissolves. Siliceous oozes, similarly are dominated by the siliceous shells of phytoplankton like diatoms and zooplankton such as radiolarians. Depending on the productivity of these planktonic organisms, the shell material that collects when these organisms die may build up a rate anywhere from 1mm to 1 cm every 1000 years.

Hydrogenous

Hydrogenous sediments are uncommon. They only occur when oceanic conditions, such as temperature or pressure, change. Rarer still are cosmogenous sediments. Hydrogenous sediments are formed from dissolved chemicals that precipitate from the ocean water or they can form by these metallic elements binding onto rocks that have really hot water of more than 300 degrees Celsius circulating around, along the mid-ocean ridges, and when elements mix with the cold sea water they precipitate from the cooling water. These, known as manganese nodules, are composed of layers of different metals like manganese, iron, nickel, cobalt, and copper and are always found on the surface of the ocean floor. Cosmogenous sediments are the remains of space debris such as comets and asteroids, made up of silicates and various metals that have impacted the Earth.

Size classification

Another way that sediments are described is through their descriptive classification. These sediments vary in size, anywhere from 1/4096 of a mm to greater than 256 mm. The different types are boulder, cobble, pebble, granule, sand, silt, and clay. Each type becomes finer in grain. The grain size indicates what type of sediment it is and the environment in which it was created. Large grains sink fast and can only be pushed by rapid flowing water (high energy environment) whereas small grains sink very slowly and can be suspended by slight water movement and accumulate in conditions where water is not moving so quickly. Therefore, larger grains of sediment come together in higher energy conditions and smaller grains in lower energy conditions.

Various amounts of these sediments are deposited around the world and get distributed in three ways—the processes of production, dilution, and destruction.

Climate change

It is known that climate affects the ocean and the ocean affects the climate. Due to climate change, as the ocean gets warmer this too has an effect on the seafloor. Because of greenhouse gasses such as carbon dioxide, this will have an effect on the bicarbonate buffer of the ocean. The bicarbonate buffer is the concentration of bicarbonate ions that keeps the ocean’s acidity balanced between a ph range of 7.5-8.4. An addition of carbon dioxide in the oceans makes the oceans more acidic. Increased ocean acidity is not good for the planktonic organisms that depend on calcium to form their shells. Calcium dissolves with very weak acids and increase in the ocean’s acidity will be destructive for the calcareous organisms. This will lead to the Calcite Compensation Depth (CCD), depth below calcite is completely dissolve, to grow in size causing the calcite to dissolve at higher depths. This will then have a great effect on the calcareous ooze in the ocean as the sediment itself would begin to dissolve.

Predictions

Calculations of global warming prepared in or before 2001 from a range of climate models under the SRES A2 emissions scenario, which assumes no action is taken to reduce emissions and regionally divided economic development.

The geographic distribution of surface warming during the 21st century calculated by the HadCM3 climate model if a business as usual scenario is assumed for economic growth and greenhouse gas emissions. In this figure, the globally averaged warming corresponds to 3.0 °C (5.4 °F).

If ocean temperatures rise it will have an effect right beneath the ocean floor and allow the addition of another greenhouse gas, methane gas. Methane gas has been found under methane hydrate, frozen methane and water, beneath the ocean floor. With the ocean warming, this methane hydrate will begin to melt and release methane gas contributing to global warming. Increase of water temperature will also have a devastating effect on different oceanic ecosystems like coral reefs. The direct effect is the coral bleaching of these reefs. These reefs live within a narrow temperature margin, so a small increase in temperature has drastic effects in these environments. When corals bleach it is because the coral loses 60-90% of their zooxanthellae due to different stressors, ocean temperature being one of them, and if the bleaching is prolonged for an uncertain amount of time the coral host dies.

Although uncertain, another effect climate change may be having is with the growth, toxicity, and distribution of harmful algal blooms. These algal blooms have serious effects on not only marine ecosystems, killing sea animals and fish with their toxins, but also for humans as well. Some of these blooms deplete the oxygen around them to such low levels that fish die. It is important that these harmful effects are noted with higher levels of awareness so that changes can be implemented before it’s too late.

See also

• History of climate change science
• Index of climate change articles
• Meltwater
• Polar ice packs
• World Ocean

Further reading

• Titus, James G. (December 1989). "The Potential Effects of Global Climate Change on the United States": 119. {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: ref duplicates default (link)
• Trujillo, Alan P.; Thurman, Harold V. (2005). Essentials of Oceanography (8th ed.). New Jersey: Pearson Education, Inc.{{cite book}}: CS1 maint: ref duplicates default (link)
• Trujillo, Alan P.; Thurman, Harold V. (2008). Essentials of oceanography (9th ed.). New Jersey: Pearson Education, Inc.{{cite book}}: CS1 maint: ref duplicates default (link)
• "Coastal Areas Impacts & Adaptation". United States Environmental Protection Agency. Retrieved June 11, 2012.

External links

• DISCOVER – satellite-based ocean and climate data since 1979 from NASA