Ocean Pollution: Rising Temperatures And Their Causes

The ocean is central to reducing global greenhouse gas emissions, absorbing approximately 90% of the excess heat caused by these gases. However, the ocean's absorption of carbon dioxide from the atmosphere is changing the pH of the water, making it more acidic. This process, known as ocean acidification, poses a significant threat to marine life, particularly coral reefs. As the ocean continues to absorb heat, marine heatwaves become more frequent and intense, causing further stress to coral reefs and leading to a phenomenon known as coral bleaching. Climate change-induced ocean warming also contributes to rising sea levels, as warmer water expands and ice sheets melt, adding more water to the oceans. These interconnected processes of ocean warming, acidification, and sea-level rise have far-reaching consequences for marine ecosystems and human communities that depend on the ocean for their livelihoods.

Greenhouse gases and ocean heat content

Greenhouse gases in the atmosphere absorb and trap energy from the sun. As the levels of greenhouse gases in the atmosphere increase, more heat is trapped, and the oceans absorb more heat. This is because most of the excess atmospheric heat is passed back to the ocean. As a result, the ocean's heat content increases, causing ocean waters to warm.

The ocean is the largest carbon sink on the planet, storing some 30% of carbon dioxide and 93% of all greenhouse gases. The ocean absorbs carbon dioxide from the atmosphere, which changes the pH of the ocean, making seawater more acidic. This process is called ocean acidification. Higher acidity affects the balance of minerals in the water, making it difficult for certain marine animals, such as corals and shellfish, to build their skeletons and shells.

The ocean's absorption of heat also contributes to sea level rise. As the ocean warms, water expands, and sea levels rise. This warming also contributes to the melting of glaciers and ice sheets around Greenland and Antarctica. The Intergovernmental Panel on Climate Change (IPCC) states that human influence has been the main driver of the ocean heat increase observed since the 1970s. Marine heatwaves have become longer-lasting, more intense, and extensive, causing widespread coral bleaching and reef degradation.

The increase in ocean temperatures also has other impacts. For example, harmful algal blooms (HABs) have been linked to increasing temperatures in the Atlantic and Pacific Oceans. These blooms can produce excessive amounts of biomass that block light from reaching below the ocean surface. As these organisms die and decompose, oxygen levels decrease, making it challenging for other organisms to survive. Additionally, some species of HABs produce toxins that are hazardous to marine life and humans.

The effects of greenhouse gases on ocean heat content and the subsequent consequences for marine ecosystems and human communities highlight the urgent need to address climate change and reduce greenhouse gas emissions.

Coral bleaching and reef degradation

Coral reefs are one of the most complex and rich ecosystems in the world. However, they are under severe threat due to rising ocean temperatures. Climate change is causing ocean waters to warm, and this warming places stress on corals. As a result, corals expel the microscopic algae that live in their tissues. These algae are essential as they produce food for the corals through photosynthesis. Corals also lose their colour or bleach without these algae, as the white colour of the calcium carbonate structure underlying the polyps is exposed.

Coral bleaching is a significant concern as it makes corals more susceptible to starvation and diseases. A temperature increase of just 1 degree Celsius for four weeks can trigger bleaching. Marine heatwaves, which have become more frequent, longer-lasting, and intense, cause mass coral bleaching events, leading to high coral mortality. The Great Barrier Reef, one of the most diverse ecosystems, has experienced unprecedented back-to-back bleaching events in 2016 and 2017, affecting two-thirds of the reef and resulting in 22% coral mortality.

The rising ocean temperatures are not the only threat to coral reefs. Ocean acidification, caused by increased carbon dioxide levels, decreases coral growth and structural integrity, making corals more vulnerable to destruction by stronger and more frequent storms. Additionally, increased runoff of freshwater, sediment, and land-based pollutants contribute to algal blooms, creating murky water conditions that block sunlight, hindering coral photosynthesis. Sediment runoff can also smother and kill corals. Climate change further affects coral reefs by altering ocean circulation patterns, leading to a lack of food for corals and disrupting coral larvae dispersal.

Human activities also directly and indirectly impact coral reefs. Land-based pollution, such as herbicides, metals, and organic chemicals, can damage coral-algal symbiosis, resulting in bleaching. Trash, microplastics, and discarded fishing gear can entangle and kill reef organisms, block sunlight, and introduce toxins into the ecosystem. Physical damage from coastal development, destructive fishing practices, and boat anchors also degrade coral reefs.

Urgent action is required to address these threats and protect coral reefs. While reducing global greenhouse gas emissions is crucial, it is equally important to make coral reefs more resilient and help them adapt to the warming temperatures.

Rising sea levels

Since 1880, sea levels have risen by over 23 centimetres (8 inches), with about six centimetres of that increase occurring since 1993. This demonstrates the acceleration of human-caused climate change over the last few decades. The rate of sea level rise is now more than 2.5 centimetres (1 inch) per decade. The rise in sea levels varies by region, with some areas projected to rise by at least 15 inches by 2100.

The impact of rising sea levels is already being felt in many parts of the world. Coastal communities are facing increasing threats to their livelihoods, including shoreline erosion, flooding, and water pollution. The frequency of coastal flooding has increased since the 1950s, with the rate of increase being the largest in most locations in Hawaii and along the East and Gulf Coasts. As sea levels continue to rise, the risk of high tides, storm surges, and other extreme weather events also increases, potentially displacing millions of people worldwide.

The ocean plays a crucial role in absorbing excess heat and carbon emissions, making it an essential ally in the fight against climate change. However, the health and stability of the ocean are at risk due to the increasing temperatures and human influence. It is important to prioritize the health of our oceans to mitigate the effects of climate change effectively.

Marine life and ecosystem shifts

Marine ecosystems are incredibly delicate, and ocean warming is already causing significant shifts in marine life. As the oceans absorb more heat, marine species are moving to cooler waters, with some fish species, for example, migrating to higher latitudes. This shift in distribution can have a profound impact on marine ecosystems, fishing communities, and coastal communities.

The Intergovernmental Panel on Climate Change (IPCC) states that human influence has been the primary driver of the ocean heat increase observed since the 1970s. Marine heatwaves have become more frequent, intense, and long-lasting, causing widespread coral bleaching and reef degradation. Coral reefs are incredibly important as they sustain a massive amount of marine biodiversity and support local economies through fisheries, tourism, and protection from storm surges and flooding.

Coral bleaching occurs when corals, under stress from higher temperatures, expel the microscopic algae that live within their tissues and provide them with food. The corals then turn white or "bleached" and become more susceptible to disease and pollution, often leading to their death. The UN Environment Programme warns that if ocean warming continues, every coral reef in the world could bleach by the end of the century.

In addition to coral reefs, other marine ecosystems are also at risk. Harmful algal blooms (HABs), or "red tides," have been linked to increasing ocean temperatures. Certain species of cyanobacteria can block light from reaching below the ocean's surface, and as they decompose, they deplete oxygen levels, making it difficult for other organisms to survive. Some HABs also produce toxins harmful to marine life and humans.

The changing ocean temperatures also impact the seasonal behaviours of marine species. For example, some fish species are spawning earlier in the year, which affects the peak fishing season and can have economic consequences for fisheries.

Ocean acidification

When carbon dioxide is absorbed by seawater, a series of chemical reactions occur, resulting in an increased concentration of hydrogen ions, which lowers the pH of the ocean, making it more acidic. This process is known as ocean acidification. Since the Industrial Revolution, the concentration of carbon dioxide in the atmosphere has increased due to human actions, and during this time, the pH of surface ocean waters has fallen by 0.1 pH units, representing a 30% increase in acidity.

In addition to shellfish, ocean acidification also affects other species such as coral reefs, which are essential for providing habitat and resilience to many marine ecosystems. The increase in acidity can lead to the dissolution of coral structures, reducing the habitat available for fish and other marine life. Algae and seagrasses, on the other hand, may benefit from higher CO2 conditions as they require CO2 for photosynthesis, similar to plants on land.

To address ocean acidification, it is crucial to transition to clean energy sources, implement stronger pollution regulations, and enhance conservation efforts to protect and restore critical carbon sinks, such as forests and wetlands. These measures will help reduce carbon emissions and mitigate the impacts of ocean acidification on marine ecosystems and human communities that depend on them.

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