How is Climate Change Affecting Ocean?

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The following are some of the effects of climate change on oceans: an increase in sea surface temperature as well as ocean temperatures at greater depths, more frequent marine heatwaves, a decrease in pH value, a rise in sea level from ocean warming and ice sheet melting, a decline in Arctic sea ice, increased upper ocean stratification, reductions in oxygen levels, increased salinity contrasts (salty areas becoming saltier and fresher areas becoming less salty) changes to ocean circulation

All of these changes have repercussions for marine ecosystems. The fundamental source of these changes is global warming induced by human-generated greenhouse gas emissions such as carbon dioxide and methane. Because the ocean absorbs the majority of the increased heat in the climate system, this unavoidably leads to ocean warming. Because the ocean absorbs part of the excess carbon dioxide in the atmosphere (through carbon sequestration), the water becomes more acidic. It is estimated that the ocean absorbs around 25% of all CO2 emissions created by humans.

Ocean temperature stratification increases when the ocean surface warms owing to rising air temperatures. The decrease in ocean layer mixing stabilises warm water at the top while decreasing cold, deep water circulation. Reduced up-and-down mixing diminishes the ocean's ability to absorb heat, diverting a greater proportion of future warming towards the atmosphere and land. The amount of energy available to tropical cyclones and other storms is predicted to grow, but nutrients for fish in the top ocean layers are expected to decrease, as is the ocean's capacity to store carbon.

These changes affect marine ecosystems, which can hasten species extinctions or induce population expansions, altering species distribution. This has an impact on coastal fishing and tourism as well. Rising sea temperatures will also affect numerous oceanic ecosystems, including coral reefs.

Changes Occurring due to Green House effect

At the moment (2022), atmospheric CO2 levels of more than 410 parts per million (ppm) are about 50% higher than preindustrial levels. These extraordinary levels and quick development rates are unique in the geological record's 55 million years. This surplus CO2 is undoubtedly human-caused, representing a combination of anthropogenic fossil fuel, industrial, and land-use/land-change emissions. The idea that the ocean serves as a primary sink for human CO2 has been discussed in scientific circles since at least the late 1950s. Several pieces of data point to the ocean absorbing around a quarter of all human CO2 emissions.

Rise in Ocean Temperature

The ocean is clearly warming as a result of climate change, and the pace of warming is growing. The worldwide ocean was the warmest it has ever been measured by mankind in 2022.  This is determined by the ocean heat content, which exceeded the previous 2021 maximum in 2022.  The gradual rise in ocean temperatures is an unavoidable result of the Earth's energy imbalance, which is principally caused by rising levels of greenhouse gases. The upper ocean (above 700 m) is warming the quickest, although the warming trend is widespread. The majority of ocean heat gain occurs in the Southern Ocean. For example, between the 1950s and the 1980s, the temperature of the Antarctic Southern Ocean rose by 0.17 °C (0.31 °F), approximately double the pace of the global ocean. The average temperature of the upper 2000 metres of the ocean grew by 0.12°C between 1960 and 2019, whereas the ocean surface temperature climbed by 1.2°C from the pre-industrial period.  The pace of warming varies with depth: at a thousand metres deep, warming happens at a rate of about 0.4 °C per century (data from 1981 to 2019), but at two kilometres depth, warming occurs at half that rate.

Ocean Heat Content

The temperature of the ocean varies depending on where you are. Temperatures are higher towards the equator and lower at the poles. As a result, increases in total ocean heat content best represent ocean warming. When comparing to 1969-1993, heat consumption increased between 1993 and 2017.

Changes in pH of Ocean

Ocean acidification is the decrease in the pH of the Earth's oceans. Between 1751 and 2021, the average pH of the ocean surface fell from around 8.25 to 8.14.  The primary source of ocean acidification is human-caused carbon dioxide emissions, which have resulted in atmospheric carbon dioxide (CO2) levels of more than 410 ppm (in 2020). CO2 from the atmosphere is absorbed by the seas.

This produces carbonic acid (H2CO3), which dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+). The presence of free hydrogen ions (H+) lowers the pH of the ocean, increasing acidity (this does not mean that seawater is acidic yet; it is still alkaline, with a pH higher than 8). The concentration of carbonate ions, which are the fundamental building blocks for calcium carbonate (CaCO3) shells and skeletons, decreases as pH decreases. Marine calcifying animals, such as molluscs, oysters, and corals, are especially vulnerable because they rely on calcium carbonate to produce shells and skeletons. The shift in pH from 8.25 to 8.14 reflects an almost 30% rise in hydrogen ion concentration in the world's seas (the pH scale is logarithmic, so a change of one in pH unit is equivalent to a tenfold change in hydrogen ion concentration). The pH and carbonate saturation levels of the sea surface change based on ocean depth and location. Colder and higher latitude seas are capable of absorbing more CO2. This can cause acidity to rise, reducing pH and carbonate saturation levels in particular areas.

Effects on the Physical Environment 

Sea Level Rise

Since around 1900, the global sea level has risen at an average pace of 1-2 mm/year (the global average sea level was about 15–25 cm higher in 2018 compared to 1900): 1318 The rate of sea level rise is increasingly increasing: from 2006 to 2018, sea level climbed by around 4 millimetres each year. Between 1901 and 2018, the average worldwide sea level rose by 15-25 cm (6-10 in), or 1-2 mm each year.  This pace is increasing, and sea levels are presently rising at a rate of 3.7 mm (0.146 inch) every year. Human-caused climate change is to blame, as it constantly warms (and hence expands) the ocean and melts land-based ice sheets and glaciers. Between 1993 and 2018, thermal expansion of water contributed 42% to sea level rise (SLR); melting of temperate glaciers contributed 21%; Greenland contributed 15%; and Antarctica contributed 8%Because sea level rise trails changes in Earth temperature, it will continue to increase between now and 2050 only as a result of already occurring warming.

Changing Ocean Currents

Ocean currents are created by temperature variations induced by sunlight and air temperatures at various latitudes, as well as prevailing winds and the varied densities of salt and fresh water. Warm air rises at the equator and cools as it goes towards the poles. Cool air descends at the poles, but warms and rises as it goes towards the equator. This produces Hadley cells, which are large-scale wind patterns, with identical factors driving a mid-latitude cell in each hemisphere. [39] Surface currents are driven by wind patterns linked with these circulation cells, which push surface water to higher latitudes where the air is cooler.

This cools the water, causing it to become exceedingly thick in comparison to lower latitude waters, leading it to sink to the ocean floor, generating North Atlantic Deep Water (NADW) in the north and Antarctic Bottom Water (AABW) in the south.

Increasing Stratification

Changes in ocean stratification are significant because they can influence productivity and oxygen levels. The division of water into strata depending on a given amount is known as stratification. Stratification by layers occurs in all ocean basins. The stratified layers operate as a barrier to water mixing, affecting the exchange of heat, carbon, oxygen, and other nutrients.

Since 1970, there has been an increase in upper ocean stratification due to global warming and changes in salinity in some areas. The fluctuations in salinity are caused by evaporation in tropical seas, which increases salinity and density, and ice melt in high latitudes, which decreases salinity.

Impact on the Weather of Earth

Climate change and ocean warming will cause extensive changes in the Earth's climate and weather system, including increasing tropical cyclone and monsoon intensities and weather extremes, with some places becoming wetter and others drier, posing a challenge to present agricultural systems. Changing wind patterns are expected to cause wave heights to rise in certain regions. This can endanger both seafarers and maritime buildings.

Tropical Cyclones 

Human-caused climate change continues to warm the seas, which serve as a repository for past effects. The ensuing environment, which includes increased ocean heat content and sea surface temperatures, energises tropical cyclones, making them more violent, larger, and longer lasting, as well as dramatically increasing flooding rainfall. Climate change can have a range of effects on tropical cyclones, including an increase in rainfall and wind speed, a drop in overall frequency, an increase in the frequency of particularly powerful storms, and a poleward expansion of where the cyclones reach maximum strength. Tropical cyclones get their energy or "fuel" from warm, wet air. As ocean temperatures rise due to climate change, there may be more of this fuel accessible.

Salinity Changes

Because of global warming and increased glacier melt, thermohaline circulation patterns may be changed when more freshwater is discharged into the seas, affecting ocean salinity. Thermohaline circulation is in charge of transporting cold, nutrient-rich water up from the ocean's depths, a process known as upwelling. Seawater is made up of both fresh water and salt, and the quantity of salt in seawater is known as salinity. Because salt does not evaporate, freshwater precipitation and evaporation have a substantial impact on salinity. Changes in the water cycle are so clearly evident in surface salinity measurements, which have been measured since the 1930s. Long-term observational data demonstrate a clear trend: global salinity trends are intensifying throughout this time span. This indicates that high-salty regions have become more saline, whereas low-saline parts have become less saline. Evaporation dominates high-salinity locations, and the rise in salinity indicates that evaporation is growing even more. The same is true for low salinity areas that are becoming less saline, indicating that precipitation is strengthening even more.

Impacts on Aquatic life 

Climate change will affect not just the total productivity of the seas, but also the organisation of the ocean biomass communities, resulting in a poleward movement of species. Since the 1950s, several species have travelled hundreds of kilometres. Phytoplankton bloom dates are also shifting earlier in the season, especially in polar regions. With additional climate change, these tendencies are expected to continue.

Climate change may also have an influence on seabirds, fish, and animals in polar areas, where species with highly specialised survival strategies may need to adjust to large changes in habitat and food availability. Furthermore, sea ice frequently plays an important part in their life cycle.

Impacts on Oceanic Calcifying Organisms

The entire ecological effects of changes in calcification caused by ocean acidification are complicated, although many calcifying animals appear to be negatively affected by ocean acidification. Ocean acidification makes it more difficult for shell-accreting organisms to get carbonate ions, which are required for the formation of their hard exoskeletal shell.

Impacts on Coral Reefs

While certain mobile marine species, such as corals, can migrate in response to climate change, this is considerably more difficult for others. A coral reef is an aquatic habitat characterised by corals that construct reefs. Reefs are made up of coral polyp colonies bound together by calcium carbonate. Coral reefs are major biodiversity hotspots and critical to many millions of people who rely on them for coastal protection, food, and tourism in many locations. Warm water corals have definitely declined, with losses of 50% in the previous 30-50 years as a result of several challenges such as ocean warming, acidification, pollution, and physical damage from activities such as fishing, and these pressures are projected to worsen.

Journal

Journal of Climatology & Weather Forecasting is an open-access journal; all the articles are peer-reviewed by eminent people in the field. Journal strives to publish and get a worthy impact factor by quick visibility through its open-access guiding principle for world-class research work. Among the Climatology list journal Climatology & Weather Forecasting has a good reach to researchers and the scientific community.

Scope: climatic change, weather forecasting, analysis techniques, nowcasting, numerical weather prediction/forecasting, cloud-resolving models, parameterization, operational forecasting, coastal meteorology, mesoscale forecasting, numerical weather prediction/forecasting.

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