Global warming can affect sea levels, coastlines, ocean acidification, ocean currents, seawater, sea surface temperatures,tides, the sea floor, weather, and trigger several changes in ocean bio-geochemistry; all of these affect the functioning of a society.
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.
The consensus of many studies of coastal tide gauge records is that during the past century sea level has risen worldwide at an average rate of 1–2 mm/yr reflecting a net flux of heat into the surface of the land and oceans. Corresponding studies based on satellite altimetry shows that this rate has increased to closer to 3 mm/yr during the more completely monitored past 20 years. A recent review of the literature  suggests that 30% of the sea level rise since 1993 is due to thermal expansion and 55% due to continental ice melt, both resulting from warming global temperatures. In another study, results estimate the heat content of the ocean in the upper 700 meters has increased significantly from 1955–2010. Observations of the changes in heat content of the ocean are important for providing realistic estimates of how the ocean is changing with global warming. An even more recent study of the contributions to global sea level due to melting of the two large ice sheets based on satellite measurements of gravity fluctuations suggests that the melting of these alone are causing global sea level to about 1 mm/yr. In a recent modeling study, scientists used an earth system model to study several variables of the ocean, one of which was the heat content of the oceans over the past several hundred years. The earth system model incorporated the atmosphere, land surface processes, and other earth components to make it more realistic and similar to observations. Results of their model simulation showed that since 1500, the ocean heat content of the upper 500 m has increased.
The connection between sea level rise and ocean thermal expansion follows from Charles's law (also known as the law of volumes) put simply states that the volume of a given mass is proportional to its temperature. This contribution to sea level is monitored by oceanographers using a succession of temperature measuring profiling instruments, which is then compiled at national data centers such as the United States National Oceanographic Data Center. The International Panel on Climate Change (IPCC) Fifth Assessment Report estimates that the upper ocean (surface to 750 m deep) has warmed by 0.09 to 0.13 degrees C per decade over the past 40 years. Other processes important in influencing global sea level include changes to groundwater storage including dams and reservoirs.
Global warming also has an enormous impact with respect to melting glaciers and ice sheets. Higher global temperatures melt glaciers such as the one in Greenland, which flow into the oceans, adding to the amount of seawater. A large rise (on 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, erodebeaches, increase the risk of flooding, and increase the salinity of estuaries, aquifers, and wetlands.”
Superimposed on the global rise in sea level, is strong regional and decadal variability which may cause sea level along a particular coastline to decline with time (for example along the Canadian eastern seaboard), or to rise faster than the global average. Regions that have shown a rapid rise in sea level during the past two decades include the western tropical Pacific and the United States northeastern seaboard. These regional variations in sea level are the result of many factors, such as local sedimentation rates, geomorphology, post-glacial rebound, and coastal erosion. Large storm events, such as Hurricane Sandy in the eastern Atlantic, can dramatically alter coastlines and affect sea level rise as well.
Coastal regions would be most affected by rising sea levels. 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.
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 a result of the erosion and ruin of properties by large storms on coastal lands, governments have looked into buying land and having residents relocate further inland. The seas now absorb much of human-generated carbon dioxide, which then affects temperature change. The oceans store 93 percent of that energy which helps keep the planet livable by moderating temperatures.
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 contribute to this dangerous trend. As a result of rising sea levels, the outer boundaries of wetlands tend to 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 a negative impact not only on coastal property and economy but on 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 respect 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. The considerable rise in sea level and the decreasing amounts of freshwater along the Atlantic and Gulf coasts would make those areas rather uninhabitable. Many economists predict that global warming will be one of the main economic threats to the West Coast, specifically in California. "Low-lying coastal areas, such as along the Gulf Coast, are particularly vulnerable to sea-level rise and stronger storms—and those risks are reflected in rising insurance rates and premiums. In Florida, for example, the average price of a homeowners’ policy increased by 77 percent between 2001 and 2006." 
Since rising sea levels present a pressing problem not only to coastal communities but to the whole global population as well, much scientific research has been performed to analyze the causes and consequences of a rise in sea level. The U.S. Geological Survey has conducted such research, addressing coastal vulnerability to sea level rise and incorporating six physical variables to analyze the changes in sea level: 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). The research was conducted on the various 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 regard 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.” For 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.”
Many humanitarians and environmentalists believe that political policy needs to have a bigger role in carbon dioxide reduction. Humans have a substantial influence on the rise of sea level because we emit increasing levels of 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.
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 nearest the equator, the hot air at 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.
Wind patterns associated with these circulation cells drive surface currents which push the surface water to the higher latitudes where the air is colder. This cools the water down enough to where it is capable of dissolving more gasses and minerals, causing 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 (NADW) in the north and Antarctic Bottom Water (AABW) in the south. Driven by this sinking and the upwelling that occurs in lower latitudes, as well as the driving force of the winds on surface water, the ocean currents act to circulate 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, reducing the density of the surface water. Consequently, the water sinks more slowly than it normally would.
It is important to note that ocean currents provide the necessary nutrients for life to sustain itself in the lower latitudes. Should the currents slow down, fewer nutrients would be brought to sustain ocean life resulting in a crumbling of the food chain and irreparable damage to 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, excess carbon has 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.
Another effect of global warming on the carbon cycle is ocean acidification. The ocean and the atmosphere constantly act 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 survival harder for planktonic organisms that depend on calcium carbonate to form their shells. A decrease in the base of the food chain will, once again, be destructive to the ecosystems to which they belong. With fewer of these photosynthetic organisms present at the surface of the ocean, less carbon will be converted to oxygen, thereby allowing the greenhouse gasses to go unchecked.
The effects of ocean acidification can already be seen and have been happening since the start of the industrial revolution, with pH levels of the ocean dropping by 0.1 since the pre-industrial revolution times. An effect called coral bleaching can be seen on the Great Barrier Reef in Australia, where ocean acidification’s effects are already taking place. Coral bleaching is when unicellular organisms that help make up the coral begin to die off and leave the coral giving it a white appearance. These unicellular organisms are important for the coral to feed and get the proper nutrition that is necessary to survive, leaving the coral weak and malnourished. This results in weaker coral that can die more easily and offer less protection to the organisms that depend on coral for shelter and protection. Increased acidity can also dissolve an organism’s shell, threatening entire groups of shellfish and zooplankton and in turn, presenting a threat to the food chain and ecosystem.
Without strong shells, surviving and growing becomes more of a challenge for marine life that depend on calcified shells. The populations of these animals becomes smaller and individual members of the species turn weaker. The fish that rely on these smaller shell constructing animals for food now have a decreased supply, and animals that need coral reefs for shelter now have less protection. The effects of ocean acidification decrease population sizes of marine life and may cause an economic disruption if enough fish die off, which can seriously harm the global economy as the fishing industry makes a lot of money worldwide.
Steps are being taken to combat the potentially devastating effects of ocean acidification, and scientists worldwide are coming together to solve the problem that is known as “global warming’s evil twin”.
Research indicates that increasing ocean temperatures are taking a toll on the marine ecosystem. A study on phytoplankton changes in the Indian Ocean indicates a decline of up to 20% in marine phytoplankton during the past six decades. During the summer, the western Indian Ocean is home to one of the largest concentrations of marine phytoplankton blooms in the world when compared to other oceans in the tropics. Increased warming in the Indian Ocean enhances ocean stratification, which prevents nutrient mixing in the euphotic zone where there is ample light available for photosynthesis. Thus, primary production is constrained and the region’s entire food web is disrupted. If rapid warming continues, experts predict that the Indian Ocean will transform into an ecological desert and will no longer be productive. The same study also addresses the abrupt decline of tuna catch rates in the Indian Ocean during the past half century. This decrease is mostly due to increased industrial fisheries, with ocean warming adding further stress to the fish species. These rates show a 50-90% decrease over 5 decades.
A study that describes climate-driven trends in contemporary ocean productivity looked at global-ocean net primary production (NPP) changes detected from satellite measurements of ocean color from 1997 to 2006. These measurements can be used to quantify ocean productivity on a global scale and relate changes to environmental factors. They found an initial increase in NPP from 1997 to 1999 followed by a continuous decrease in productivity after 1999. These trends are propelled by the expansive stratified low-latitude oceans and are closely linked to climate variability. This relationship between the physical environment and ocean biology effects the availability of nutrients for phytoplankton growth since these factors influence variations in upper-ocean temperature and stratification. The downward trends of ocean productivity after 1999 observed in this study can give insight into how climate change can affect marine life in the future.
Global warming also affects weather patterns as they pertain 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 would get warmer and warmer regions would get much warmer. However, there is also speculation that the complete opposite could be true. A warmer earth could serve to moderate temperatures worldwide. There is still much that is not understood about the earth’s climate, because it is very difficult to make climate models. As such, predicting the effects that global warming might have on our planet is still an inexact science. Global warming is also causing the amount of hazards on the ocean to increase. It has increased the amount of fog at sea level, making it harder for ships to navigate without crashing into other boats or other objects in the ocean. The warmness and dampness of the ground is causing the fog to come closer to the surface level of the ocean. As the rain falls it makes the ground wet, then the warm air rises leaving a layer of cold air that turns into fog causing an unsafe ocean for travel and for working conditions on the ocean. It is also causing the ocean to create more floods due to the fact that it is warming up and the glaciers from the ice age are now melting causing the sea levels to rise, which causes the ocean to take over part of the land and beaches. Glaciers are melting at an alarming rate which is causing the ocean to rise faster than predicted. Inside of this ice there are traces of bubbles that are filled with CO2 that are then released into the atomosphere when they melt causing the greenhouse effect to grow at an even faster rate.
The contents of the ocean floor vary diversely in their origin, from eroded land materials carried into the ocean by rivers or wind flow, waste and decompositions of sea animals, and precipitation of chemicals within the sea water itself, including some from outer space. There are four basic types of sediment of the sea floor: 1.) "Terrigenous" describes the sediment derived from the materials eroded by rain, rivers, glaciers and that which is blown into the ocean by the wind, such as volcanic ash. 2.) Biogenous material is the sediment made up of the hard parts of sea animals that accumulate on the bottom of the ocean. 3.) Hydrogenous sediment is the dissolved material that precipitates in the ocean when oceanic conditions change, and 4.) cosmogenous sediment comes from extraterrestrial sources. These are the components that make up the seafloor under their genetic classifications.
Terrigenous and biogenous
Terrigenous sediment is the most abundant sediment found on the seafloor, followed by biogenous sediment. The sediment in areas of the ocean floor which is at least 30% biogenous materials is 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 deeper than about 4,000 to 5,000 meters because at further depths the calcium dissolves. Similarly, Siliceous oozes 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 at a rate anywhere from 1mm to 1 cm every 1000 years.
Hydrogenous and cosmogenous
Hydrogenous sediments are uncommon. They only occur with changes in oceanic conditions such as temperature and pressure. Rarer still are cosmogenous sediments. Hydrogenous sediments are formed from dissolved chemicals that precipitate from the ocean water, or along the mid-ocean ridges, they can form by metallic elements binding onto rocks that have water of more than 300 degrees Celsius circulating around them. When these elements mix with the cold sea water they precipitate from the cooling water. Known as manganese nodules, they are composed of layers of different metals like manganese, iron, nickel, cobalt, and copper, and they 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.
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 becoming finer in grain. The grain size indicates the type of sediment and the environment in which it was created. Larger grains sink faster 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, accumulating in conditions where water is not moving so quickly. This means that larger grains of sediment may come together in higher energy conditions and smaller grains in lower energy conditions.
Various amounts of these sediments are deposited around the world and are distributed in three ways: by the processes of production, dilution, and destruction.
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 gases such as carbon dioxide, this warming 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 within a pH range of 7.5–8.4. Addition of carbon dioxide to the ocean water 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 any increase in the ocean's acidity will be destructive for the calcareous organisms. Increased ocean acidity will lead to decreased Calcite Compensation Depth (CCD), causing calcite to dissolve in shallower waters. This will then have a great effect on the calcareous ooze in the ocean, because the sediment itself would begin to dissolve.
If ocean temperatures rise it will have an effect right beneath the ocean floor and it will 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. However, recent research has found that CO2 uptake outpaces methane release in these areas of the ocean causing overall decreases in 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, which live within a narrow temperature margin, so a small increase in temperature would have a drastic effects in these environments. When corals bleach it is because the coral loses 60–90% of their zooxanthellae due to various stressors, ocean temperature being one of them. If the bleaching is prolonged, the coral host would die.
Although uncertain, another effect of climate change may be 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 levels low enough to kill fish.
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- DISCOVER – satellite-based ocean and climate data since 1979 from NASA
Calculations 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).
Regional effects of global warming are long-term significant changes in the expected patterns of average weather of a specific region due to global warming. The world average temperature is rising due to the greenhouse effect caused by increasing levels of greenhouse gases, especially carbon dioxide. When the global temperature changes, the changes in climate are not expected to be uniform across the Earth. In particular, land areas change more quickly than oceans, and northern high latitudes change more quickly than the tropics, and the margins of biome regions change faster than do their cores.
Regional effects of global warming vary in nature. Some are the result of a generalised global change, such as rising temperature, resulting in local effects, such as melting ice. In other cases, a change may be related to a change in a particular ocean current or weather system. In such cases, the regional effect may be disproportionate and will not necessarily follow the global trend. The increasing temperatures from greenhouse gases have been causing sea levels to rise for many years.
There are three major ways in which global warming will make changes to regional climate: melting or forming ice, changing the hydrological cycle (of evaporation and precipitation) and changing currents in the oceans and air flows in the atmosphere. The coast can also be considered a region, and will suffer severe impacts from sea level rise.
Main article: Effects of global warming on human health
Highlights of recent and projected regional impacts are shown below:
Impacts on Africa
Main article: Climate change in Africa
- Africa is one of the most vulnerable continents to climate variability and change because of multiple existing stresses and low adaptive capacity. Existing stresses include poverty, political conflicts, and ecosystem degradation.
- By 2050, between 350 million and 600 million people are projected to experience increased water stress due to climate change
- Climate variability and change is projected to severely compromise agricultural production, including access to food, across Africa
- Toward the end of the 21st century, projected sea level rise will likely affect low-lying coastal areas with large populations
- Climate variability and change can negatively impact human health. In many African countries, other factors already threaten human health. For example, malaria threatens health in southern Africa and the Eastern Highlands.
Impacts on Arctic and Antarctic
- Climate change in the Arctic will likely reduce the thickness and extent of glaciers and ice sheets.
- Changes in natural ecosystems will likely have detrimental effects on many organisms including migratory birds, mammals, and higher predators. Climate change will likely cause changes in dominance structures in plant communities, with shrubs expanding 
- In the Arctic, climate changes will likely reduce the extent of sea ice and permafrost, which can have mixed effects on human settlements. Negative impacts could include damage to infrastructure and changes to winter activities such as ice fishing and ice road transportation. Positive impacts could include more navigable northern sea routes.
- The reduction and melting of permafrost, sea level rise, and stronger storms may worsen coastal erosion.
- Terrestrial and marine ecosystems and habitats are projected to be at risk to invasive species, as climatic barriers are lowered in both polar regions.
Impacts on Asia
Further information: Effects of global warming on South Asia, Effects of global warming in China, and Effects of global warming in Thailand
- Glaciers in Asia are melting at a faster rate than ever documented in historical records. Melting glaciers increase the risks of flooding and rock avalanches from destabilized slopes.
- Climate change is projected to decrease freshwater availability in central, south, east and southeast Asia, particularly in large river basins. With population growth and increasing demand from higher standards of living, this decrease could adversely affect more than a billion people by the 2050s.
- Increased flooding from the sea and, in some cases, from rivers, threatens coastal areas, especially heavily populated delta regions in south, east, and southeast Asia.
- By the mid-21st century, crop yields could increase up to 20% in east and southeast Asia. In the same period, yields could decrease up to 30% in central and south Asia.
- Sickness and death due to diarrhoeal disease are projected to increase in east, south, and southeast Asia due to projected changes in the hydrological cycle associated with climate change.
Impacts on Europe
Main article: Climate change in Europe
- Wide-ranging impacts of climate change have already been documented in Europe. These impacts include retreating glaciers, longer growing seasons, species range shifts, and heat wave-related health impacts.
- Future impacts of climate change are projected to negatively affect nearly all European regions. Many economic sectors, such as agriculture and energy, could face challenges.
- In southern Europe, higher temperatures and drought may reduce water availability, hydropower potential, summer tourism, and crop productivity.
- In central and eastern Europe, summer precipitation is projected to decrease, causing higher water stress. Forest productivity is projected to decline. The frequency of peatland fires is projected to increase.
- In northern Europe, climate change is initially projected to bring mixed effects, including some benefits such as reduced demand for heating, increased crop yields, and increased forest growth. However, as climate change continues, negative impacts are likely to outweigh benefits. These include more frequent winter floods, endangered ecosystems, and increasing ground instability.
Impacts on Latin America
- By mid-century, increases in temperature and decreases in soil moisture are projected to cause savanna to gradually replace tropical forest in the eastern Amazon basin.
- In drier areas, climate change will likely worsen drought, leading to salinization (increased salt content) and desertification (land degradation) of agricultural land. The productivity of livestock and some important crops such as maize and coffee is projected to decrease, with adverse consequences for food security. In temperate zones, soybean yields are projected to increase.
- Sea level rise is projected to increase risk of flooding, displacement of people, salinization of drinking water resources, and coastal erosion in low-lying areas.
- Changes in precipitation patterns and the melting of glaciers are projected to significantly affect water availability for human consumption, agriculture, and energy generation.
Impacts on North America
Further information: Global warming in Canada and Effects of climate change in the United States
- Warming in western mountains is projected to decrease snowpack, increase winter flooding, and reduce summer flows, exacerbating competition for over-allocated water resources.
- Disturbances from pests, diseases, and fire are projected to increasingly affect forests, with extended periods of high fire risk and large increases in area burned.
- Moderate climate change in the early decades of the century is projected to increase aggregate yields of rain-fed agriculture by 5-20%, but with important variability among regions. Crops that are near the warm end of their suitable range or that depend on highly utilized water resources will likely face major challenges.
- Increases in the number, intensity, and duration of heat waves during the course of the century are projected to further challenge cities that currently experience heat waves, with potential for adverse health impacts. Older populations are most at risk.
- Climate change will likely increasingly stress coastal communities and habitats, worsening the existing stresses of development and pollution.
Impacts on Oceania
Main articles: Effects of global warming on Australia and Climate change in New Zealand
Impacts on Small Islands
- Small islands, whether located in the tropics or higher latitudes, are already exposed to extreme weather events and changes in sea level. This existing exposure will likely make these areas sensitive to the effects of climate change.
- Deterioration in coastal conditions, such as beach erosion and coral bleaching, will likely affect local resources such as fisheries, as well as the value of tourism destinations.
- Sea level rise is projected to worsen inundation, storm surge, erosion, and other coastal hazards. These impacts would threaten vital infrastructure, settlements, and facilities that support the livelihood of island communities.
- By mid-century, on many small islands (such as the Caribbean and Pacific), climate change is projected to reduce already limited water resources to the point that they become insufficient to meet demand during low-rainfall periods.
- Invasion by non-native species is projected to increase with higher temperatures, particularly in mid- and high-latitude islands.
Inundation, displacement, and national sovereignty of small islands
According to scholar Tsosie, environmental disparities among disadvantaged communities including poor and racial minorities, extend to global inequalities between the developed and developing countries. For example, according to Barnett, J. and Adger, W.N. the projected damage to small islands and atoll communities will be a consequence of climate change caused by developing countries that will disproportionately affect these developing nations.
Sea-level rise and increased tropical cyclones are expected to place low-lying small islands in the Pacific, Indian, and Caribbean regions at risk of inundation and population displacement.
According to N. Mimura's study on the vulnerability of island countries in the South Pacific to sea level rise and climate change, financially burdened island populations living in the lowest-lying regions are most vulnerable to risks of inundation and displacement. On the islands of Fiji, Tonga and western Samoa for example, high concentrations of migrants that have moved from outer islands inhabit low and unsafe areas along the coasts.
Atoll nations, which include countries that are composed entirely of the smallest form of islands, called motus, are at risk of entire population displacement. These nations include Kiribati, Maldives, the Marshall Islands, Tokelau, and Tuvalu. According to a study on climate dangers to atoll countries, characteristics of atoll islands that make them vulnerable to sea level rise and other climate change impacts include their small size, their isolation from other land, their low income resources, and their lack of protective infrastructure.
A study that engaged the experiences of residents in atoll communities found that the cultural identities of these populations are strongly tied to these lands. The risk of losing these lands therefore threatens the national sovereignty, or right to self-determination, of Atoll nations. Human rights activists argue that the potential loss of entire atoll countries, and consequently the loss of cultures and indigenous lifeways cannot be compensated with financial means. Some researchers suggest that the focus of international dialogues on these issues should shift from ways to relocate entire communities to strategies that instead allow for these communities to remain on their lands.
Especially affected regions
The Arctic, Africa, small islands and Asianmegadeltas are regions that are likely to be especially affected by future climate change.
Within other areas, some people are particularly at risk from future climate change, such as the poor, young children and the elderly.
The Arctic is likely to be especially affected by climate change because of the high projected rate of regional warming and associated impacts. Temperature projections for the Arctic region were assessed by Anisimov et al. (2007). These suggested areally averaged warming of about 2 °C to 9 °C by the year 2100. The range reflects different projections made by different climate models, run with different forcing scenarios. Radiative forcing is a measure of the effect of natural and human activities on the climate. Different forcing scenarios reflect, for example, different projections of future human greenhouse gas emissions.
See also: Water scarcity in Africa
Africa is likely to be the continent most vulnerable to climate change. With high confidence, Boko et al. (2007) projected that in many African countries and regions, agricultural production and food security would probably be severely compromised by climate change and climate variability.
The United Nations Environment Programme (UNEP, 2007) produced a post-conflict environmental assessment of Sudan. According to UNEP (2007), environmental stresses in Sudan are interlinked with other social, economic and political issues, such as population displacement and competition over natural resources. Regional climate change, through decreased precipitation, was thought to have been one of the factors which contributed to the conflict in Darfur. Along with other environmental issues, climate change could negatively affect future development in Sudan. One of the recommendations made by UNEP (2007) was for the international community to assist Sudan in adapting to climate change.
On small islands, sea level rise is expected to exacerbate inundation, erosion and other coastal hazards, and threaten vital infrastructure, human settlements and facilities that support the livelihood of island communities. In the coastal zone of Asia, there are 11 megadeltas with an area greater than 10,000 km2. These megadeltas are homes to millions of people, and contain diverse ecosystems. Climate change and sea level rise could increase the frequency and level of inundation of Asian megadeltas due to storm surges and floods from river drainage.
Permanent ice cover on land is a result of a combination of low peak temperatures and sufficient precipitation. Some of the coldest places on Earth, such as the dry valleys of Antarctica, lack significant ice or snow coverage due to a lack of snow. Sea ice however maybe formed simply by low temperature, although precipitation may influence its stability by changing albedo, providing an insulating covering of snow and affecting heat transfer. Global warming has the capacity to alter both precipitation and temperature, resulting in significant changes to ice cover. Furthermore, the behaviour of ice sheets, ice caps and glaciers is altered by changes in temperature and precipitation, particularly as regards the behaviour of water flowing into and through the ice.
Arctic sea ice
Main article: Arctic shrinkage
Recent projections of sea ice loss suggest that the Arctic ocean will likely be free of summer sea ice sometime between 2059 and 2078.
Models showing decreasing sea ice also show a corresponding decrease in polar bear habitat. Some scientists see the polar bear as a species which will be affected first and most severely by global warming because it is a top-level predator in the Arctic, which is projected to warm more than the global average. Recent reports show polar bears resorting to cannibalism, and scientists state that these are the only instances that they have observed of polar bears stalking and killing one another for food.
Further information: Global warming in Antarctica
The Antarctic peninsula has lost a number of ice shelves recently. These are large areas of floating ice which are fed by glaciers. Many are the size of a small country. The sudden collapse of the Larsen Bice shelf in 2002 took 5 weeks or less and may have been due to global warming. Larsen B had previously been stable for up to 12,000 years.
Concern has been expressed about the stability of the West Antarctic ice sheet. A collapse of the West Antarctic ice sheet could occur "within 300 years [as] a worst-case scenario. Rapid sea-level rise (>1 m per century) is more likely to come from the WAIS than from the [Greenland ice sheet]."
As the Greenland ice sheet loses mass from calving of icebergs as well as by melting of ice, any such processes tend to accelerate the loss of the ice sheet.
The IPCC suggest that Greenland will become ice free at around 5 Celsius degrees over pre-industrial levels, but subsequent research comparing data from the Eemian period suggests that the ice sheet will remain at least in part at these temperatures. The volume of ice in the Greenland sheet is sufficient to cause a global sea level rise of 7 meters. It would take 3,000 years to completely melt the Greenland ice sheet. This figure was derived from the assumed levels of greenhouse gases over the duration of the experiment. In reality, these greenhouse gas levels are of course affected by future emissions and may differ from the assumptions made in the model.
Main article: Retreat of glaciers since 1850
Glacier retreat not only affects the communities and ecosystems around the actual glacier, but the entire downstream region. The most notable example of this is in India, where river systems such as the Indus and Ganges are ultimately fed by glacial meltwater from the Himalayas. Loss of these glaciers will have dramatic effects on the downstream region, increasing the risk of drought as lower flows of meltwater reduce summer river flows unless summer precipitation increases. Altered patterns of flooding can also affect soil fertility.
The Tibetan Plateau contains the world's third-largest store of ice. Qin Dahe, the former head of the China Meteorological Administration, said that the recent fast pace of melting and warmer temperatures will be good for agriculture and tourism in the short term; but issued a strong warning:
"Temperatures are rising four times faster than elsewhere in China, and the Tibetan glaciers are retreating at a higher speed than in any other part of the world.... In the short term, this will cause lakes to expand and bring floods and mudflows. . . . In the long run, the glaciers are vital lifelines for Asian rivers, including the Indus and the Ganges. Once they vanish, water supplies in those regions will be in peril."
See also: Climate change in Russia
Regions of permafrost cover much of the Arctic. In many areas, permafrost is melting, leading to the formation of a boggy, undulating landscape filled with thermokarst lakes and distinctive patterns of drunken trees. The process of permafrost melting is complex and poorly understood since existing models do not include feedback effects such as the heat generated by decomposition.
Arctic permafrost soils are estimated to store twice as much carbon as is currently present in the atmosphere in the form of CO2. Warming in the Arctic is causing increased emissions of CO2 and Methane (CH4).
Precipitation and vegetation changes
Much of the effect of global warming is felt through its influence on rain and snow. Regions may become wetter, drier, or may experience changes in the intensity of precipitation - such as moving from a damp climate to one defined by a mixture of floods and droughts. These changes may have a very severe impact on both the natural world and human civilisation, as both naturally occurring and farmed plants experience regional climate change that is beyond their ability to tolerate.
A U.S. National Oceanic and Atmospheric Administration (NOAA) analysis published in the Journal of Climate October 2011, and cited on Joseph J. Romm's, climateprogress.org, found that increasing droughts in the Middle East during the wintertime when the region traditionally receives most of its rainfall to replenish aquifers, and anthropogenic climate change is partly responsible. Per Earth System Research Laboratory's Martin Hoerling “The magnitude and frequency of the drying that has occurred is too great to be explained by natural variability alone,” and “This is not encouraging news for a region that already experiences water stress, because it implies natural variability alone is unlikely to return the region’s climate to normal.” the lead author of the paper. Twelve of the world’s fifteen most water-scarce countries — Bahrain, Qatar, Algeria, Libya, Tunisia, Jordan, Saudi Arabia, Yemen, Oman, the United Arab Emirates, Kuwait, Israel and Palestine — are in the Middle East.
Arctic and Alpine regions
Polar and alpine ecosystems are assumed to be particularly vulnerable to climate change as their organisms dwell at temperatures just above the zero degree threshold for a very short summer growing season. Predicted changes in climate over the next 100 years are expected to be substantial in arctic and sub-arctic regions. Already there is evidence of upward shifts of plants in mountains and in arctic shrubs are predicted to increase substantially to warming 
One modeling study suggested that the extent of the Amazon rainforest may be reduced by 70% if global warming continues unchecked, due to regional precipitation changes that result from weakening of large-scale tropical circulation.
Some studies suggest that the Sahara desert may have been more vegetated during the warmer Mid-Holocene period, and that future warming may result in similar patterns.
Some studies have found a greening of the Sahel due to global warming. Other climate models predict "a doubling of the number of anomalously dry years [in the Sahel] by the end of the century".
Expansion of subtropicaldeserts is expected as a result of global warming, due to expansion of the Hadley Cell.
Global sea level is currently rising due to the thermal expansion of water in the oceans and the addition of water from ice sheets. Because of this, there low-lying coastal areas, many of which are heavily populated, are at risk of flooding.
Areas threatened by current sea level rise include Tuvalu and the Maldives.[unreliable source?] Regions that are prone to storm surges, such as London, are also threatened.
With very high confidence, IPCC (2007) projected that by the 2080s, many millions more people would experience floods every year due to sea level rise. The numbers affected were projected to be largest in the densely populated and low-lying megadeltas of Asia and Africa. Small islands were judged to be especially vulnerable.
North Atlantic region
See also: Shutdown of thermohaline circulation
It has been suggested that a shutdown of the Atlantic thermohaline circulation may result in relative cooling of the North Atlantic region by up to 8C in certain locations. Recent research suggests that this process is not currently underway.
Tropical surface and troposphere temperatures
In the tropics, basic physical considerations, climate models, and multiple independent data sets indicate that the warming trend due to well-mixed greenhouse gases should be faster in the troposphere than at the surface.
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Mean surface temperature change for 1999–2008 relative to the average temperatures from 1940 to 1980
Projected changes in average temperatures across the world in the 2050s under three greenhouse gas (GHG) emissions scenarios, relative to average temperatures between 1971-1999