Debapriya Mukherjee
For centuries, we thought that our vast ocean was limitless and immune to human impacts. Upon death of 100,000 marine mammals ( whales, dolphins, porpoises, seals and sea lions ) and 1 million seabirds per year globally as a result of plastic pollution, we have realized - the ocean environments in danger. Further, climate change is heating the oceans and altering their chemistry so dramatically that it is threatening seafood supplies, fueling cyclones and floods and posing profound risks to the hundreds of millions of people living along the coasts. As per the record, the 10 years to the end of 2019 have been confirmed as the warmest decade and the amount of heat have been put in the world’s oceans in the past 25 years equals to 3.6 billion Hiroshima atom-bomb. Last year ocean temperature was 0.075 C above the 1981-2010 average. This measured ocean warming is irrefutable and is further proof of global warming. As the planet warms, ice sheets and glaciers melt and warming sea water expands leading to increasing the volume of the world’s oceans and sea level rise that is another climate change’s danger. As sea levels continue to rise throughout the century, chronic flooding will spread and more land will be permanently lost to the ocean.
Human activities are the major cause of endangering our most valuable ocean ecosystems. For supplementing this view, some examples are stated. The discarded plastics and other residential waste, discharge from industries and agricultural areas without adopting any effective cleaning practices eventually find their way into the sea with devastating consequences for marine life and the habitats. The amount of discarded plastics will outweigh the amount of fish in our oceans by 2050 as reported. Shipping accidents and oil spills add additional toxins to the mix. About 25 major accidents and many smaller ones cause spillage of more than 700 tons of crude oil into the sea. In addition to this, deliberate dumping from vessels (mainly during the illegal cleaning of tankers) on the high seas further aggravates this problem. Some 140,000 tons of ballast water carried by merchant vessels, which is often taken up in one port and released in another faraway from the point of origin, is ultimately dumped into the sea. Some of the species (including pathogens) in ballast water may be introduced in a new ecosystem leading to serious damage to the local flora and fauna. In addition to these, carbon emissions from human activities are causing ocean warming, acidification and oxygen loss with some evidence of changes in nutrient cycling and primary production. Oxygen in the oceans is being lost at an unprecedented rate leading to proliferation of “dead zones” on account of the climate emergency and intensive farming. Overfishing endangers ocean ecosystems and the billions of people who rely on seafood as a key source of protein. If fossil-fuel emissions continue to rise rapidly, for instance, the maximum amount of fish in the ocean that can be sustainably caught could decrease by as much as a quarter by century’s end. In addition, rapid urbanization along the world’s coastlines has seen the growth of coastal ‘megacities’ like Mumbai. Many of these populations put pressure on infrastructure where urban waste and sewage management is poor. Thereby ecosystems are changing, food webs are changing, fish stocks are changing, and this turmoil is affecting humans.
The world has been a witness to one of the biggest threats to our oceans on account of man-made pollution despite knowing the fact that ocean is the heart of the planet covering more than two-thirds of the Earth’s surface. Coral forests, mountains, volcanoes, minerals, microbes, algae, complex plants, mammals, fish, reptiles, birds, crustaceans, mollusks and a very long list of life forms including unknown forms are present in the oceans covering 370 million square km containing 1.4 billion cubic km of water. These ocean environments support a remarkable biodiversity maintaining a large number of different species ranging from microbes to marine mammals and form a wide variety of ecosystems from coastal areas to abysses more than 11,000 m deep. Contrary to popular belief, sea plants produce 70% of the oxygen (phytoplankton and marine plants exchange some 200,000 million tons of CO2/O2) whereas rainforests produce 28% oxygen. Phytoplankton- the tiny little organism, which spends its life being carried by oceanic currents, act in the same way as tree leaves do on land. Everyone loves the ocean and enjoys by watching the waves come in and out but does not realize the function of this tiny organisms as the Earth’s lungs and role to create the ozone layer that protect us from harmful ultraviolet-B rays. Furthermore, evaporated seawater forms clouds which empty their contents over the earth to create rivers, lakes and other ecosystems as well as provide the levels of moisture necessary to sustain life.
The deep waters are home to wildlife and some of the biggest creatures on earth that provides us with food, jobs, life, entertainment, and sailing and key services like climate regulation, through the energy budget, carbon cycle and nutrient cycle. For decades, the oceans have served as a crucial buffer against global warming, soaking up roughly a quarter of the carbon dioxide emitting from anthropogenic activities and absorbing more than 90 percent of the excess heat trapped on Earth by carbon dioxide and other greenhouse gases. Without that protection, the land would be heating much more rapidly and holding 97% of the water of our planet, almost all rain that drops on land comes from the sea.
Despite its significant importance to humanity, the governments in many countries simply violate the norms of probity and overlook the acts of unethical practices of discharging untreated waste , over-fishing and over-hunting, mining, the destruction of the oceans’ richest areas, the massive occupation of the coasts and the alteration of their chemical composition and temperature. Almost 80% of the pollutants dumped into the sea come from inland operations , either through rivers, direct dumping and coastal drainage (44%), or transported through the atmosphere (33%). The remaining 20% come from accidental or deliberate spills from vessels and marine facilities. From coral bleaching to sea level rise, entire marine ecosystems are rapidly changing.
Though natural formation of dead zone that is low oxygen (hypoxic) areas to small extent, can not be ruled out but excessive nutrients from sewage outfalls and agricultural runoff containing residual fertilizer have triggered the number of dead zones, where most marine life cannot survive, resulting in the collapse of some ecosystems. There are now close to 500 dead zones covering more than 245,000 km² globally. One such zone is present off the west coast of India, in the Arabian Sea. The bright green colour of the water in winter is the clear evident of the excessive delivery of nutrients from agriculture and urban centres that stimulates algal productivity, and the subsequent microbial degradation of this organic matter reduces oxygen levels, contributing towards hypoxia. In reality, low oxygen waters are also related to the acidified waters. So Hypoxia and acidification are increasingly co-occurring in the ocean and have additive and synergistic negative effects on the growth, survival, and metamorphosis of early life stage bivalves. Rising levels of atmospheric CO2 due to the burning of fossil fuels are exacerbating the ocean acidification. Since the industrial revolution, the average pH of the ocean has been found to have fallen from 8.2 to 8.1, which may seem small but corresponds to an increase in acidity of about 26%. Many marine creatures have shells and skeletons of calcium carbonate (basically chalk), which can erode as pH falls. Ocean acidification prompts some plankton species to grow faster, while slowing growth for several others, disrupting the natural linkages and competition between species and putting entire ocean ecosystems at risk. As acidification worsens and the sea surface warms, the ocean becomes less effective in absorbing CO2. The fate and behaviour of contaminants in the environment, particularly their persistence, their ability to be taken up by organisms and how they behave once absorbed, is strongly driven by environmental factors such as salinity, pH and temperature – and these are all subject to change under climate change scenarios. This means, organisms may be more or less susceptible to pollutants; the degree of change will depend on the specific pollutants and the organism species involved.
The above observations have clearly established severe consequences for both humanity and nature. Now there is the urgency of timely, ambitious, coordinated and enduring action. Now implementing effective waste reduction initiatives, recycling and effective waste and sewage management as well as sharp reduction of green house gas emission are the keys to improving the healthy longevity of our oceans. As Fish populations are already declining in many regions as warming waters throw marine ecosystems into disarray, fishery managers will need to crack down on unsustainable fishing practices to prevent seafood stocks from collapsing otherwise we face a food crisis. Nations could also expand protected areas of the ocean to help marine ecosystems stay resilient against shifting conditions. The crisis in our fisheries and in our oceans and climate are not mutually exclusive problems to be addressed separately – it is imperative that we move forward with comprehensive solutions to address them.
The writer is Former Senior Scientist, Central Pollution Control Board based in Kolkata and can be reached at 919432370163 & 916290099509 or
[email protected]