Three-quarters of the world is water and restare land. Three-quarters of the waterbody consists of oceans or seas. This sea has always been devoted to the welfare of mankind in various ways. How these seas, have been silently contributing to human civilization can be known in detail from the following text.
Almost half of world's population lives within 50 miles of the ocean and it provides us with a variety of invaluable benefits and services, including our food resources. The world's oceans play a major role in freshwater cycle. Clouds form from the sea, bringing rain and replenishing our fresh water supply. Oceans strongly influence climate and weather patterns, transfer heat and regulate amount of CO2 in atmosphere. Oceans play an important role in the Earth's carbon cycle, removing carbon from upper layers of the atmosphere and oceans. Marine plants also act as carbon sinks by sequestering carbon in seafloor sediments. Through this natural storage process, the ocean is providing a climate services.
Sea plants not only produce half of the world's oxygen, but the ocean acts as an "air-filtering device" by absorbing nearly a third of human-caused CO2 emissions. More than 90 percent of world trade is done by sea-going shipping. Marine fisheries contributed an estimated US$ 274 billion to global GDP in 2007 (World Bank, 2012) and approximately US$ 143 billion annually in seafood trade (FAO, 2018). Fisheries and aquaculture provide employment to approximately 200 million people who work along value chain and help meet nutritional needs of 3 billion people who depend on fish for their food security (FAO, 2016).
Ocean freight contributes more than half a trillion US dollars in annual revenue and is an important source of employment both at sea and inland. Global freight demand is projected to triple by 2050, depending on climate change and climate policy impacts. In 2018, international maritime trade reached an all-time high of 11 billion tons loaded. Industries such as fishing, tourism, and transportation provide essential revenues, and in the United States alone, marine tourism, recreation, and lifestyle resources add more than $128 billion to annual GDP. Marine plants and aquatic sources are making essential medicinal products for the human body. Recreation or spending time at the seaside is an effective therapeutic for body, mind, and spirit.
Greenhouse gases (GHG) such as methane and CO2 occur naturally in Earth's atmosphere. Their density has increased anthropogenically through burning of coal and natural gas, increased animal husbandry, and deforestation. Since the pre-industrial era, humans have emitted 2,500 billion tons of CO2, exceeding average natural levels over past 650,000 years (IPCC, 2021). So far, 10 countries have contributed 69 percent of global GHG emissions, and 20 countries accounted for nearly 82 percent of global CO2 emissions from 1990 to 2019. Although the 50 developing countries contribute less than 1 percent of global emissions, climate change is disproportionately affecting developing countries, particularly marginalized populations.
Thanks to the contributions of more than 100 scientists from 30 countries, as well as support of Iceland, UNESCO published the State of the Oceans Report 2024, which provides an evidence-based review of challenges including ocean warming, sea level rise, pollution, acidification, de-oxygenation, blue carbon and biodiversity loss. While atmospheric temperature tends to fluctuate, ocean warms steadily and continuously.
According to the Ocean Report 2024, oceans are now warming at twice rate of twenty years ago, with highest increase since the 1950s in 2023. While Paris Agreement pledged to keep global warming below 2°C above pre-industrial levels, ocean temperatures have already increased by an average of 1.45°C, with clear hotspots above 2°C in the Mediterranean, tropical Atlantic and Southern Oceans. One dramatic consequence of this warming is rising sea levels around the world. Oceans absorb 90 percent of excess heat released into atmosphere and expand as water warms.
Since 1960s, ocean has lost 2 percent of its oxygen due to warming and pollutants, including wastewater and agriculture. About 500 "dead zones" have been identified in subtropical zone where almost no marine life remains due to reduced oxygen content. As 25-30 percent of fossil fuel emissions are absorbed by the ocean, this excess of CO2 is reshaping ocean's chemical composition. Since pre-industrial times, ocean temperatures have increased by 30 percent and will reach 170 percent by 2100, causing mass die-offs of marine species.
1.7 million tons plastic waste ends up in the ocean. In addition, cigarette butts, ocean dumping or washing of garbage in waterways, testing of harmful defense weapons, and many other types of floating garbage are dumped into the sea. According to United Nations 2017, there will be more plastic than fish in the ocean by 2050 if adequate action is not taken.
According to the UNESCO report, the most promising is that marine forests, including mangroves, sea grasses, and tidal marshes, can absorb 5 times more carbon than terrestrial forests.
In other words, apart from biodiversity, mangrove forests act as the best defense against global warming. As long as GHG continue to rise, sea level rise will continue. One study found that, 20th century depression was responsible for most of sea level rise in about 3,000 years. Global average sea level rise has become a hot topic in recent years. Because rising sea levels could inundate low-lying subtropical regions around the world and even cause entire cities to disappear. Due to climate change, sea level rise in Bangladesh is causing frequent severe flooding in low-lying subtropical areas of the Bay of Bengal.
In 2019 Special Report Oceans and Cryosphere on a Changing Climate, scientists agree that melting glaciers and thermal expansion of seawater due to global warming are main drivers of global average sea level rise. Although sea level rise began in early 19th century, rate of increase has accelerated in recent decades due to global warming, melting of glaciers and ice sheets. During most of the 20th century, sea level rose at a rate of 1.4 millimeters per year, and between 2006 and 2015, the rate nearly doubled to about 3.6 millimeters per year. In Bangladesh, one of the world's most vulnerable countries to climate change, an estimated 3.5 million people are at risk of river flooding each year due to rising sea levels and increasingly intense monsoon seasons. According to UN predictions, if global warming continues at the current rate, about 17 percent or about 30 million Bangladeshis will have to relocate in next decade.
Bangladesh is a low-lying sub-continental country located between India and Myanmar in South Asia. 60 percent of the country's land is less than 5 meters above sea level, and most of cities are populated in low-lying subtropical areas. The country is crossed by several rivers such as the Brakshaputra and the Padma which originate in the Himalayas and flow into the Bay of Bengal.
Bangladesh is located on the windward slopes of the Himalayas, an area that is subject to orographic rainfall, especially during monsoon from June to October.Rain occurs when moist air from sea moves over the mountains.
It is necessary to build high and paved dams in sub-districts of Bangladesh and to build a lot of infrastructure to protect cities, which requires financial support of the international community.
IPCC has made clear in recent reports that, no amount of emissions reductions can stop the near- and medium-term effects of sea level rise. Even if all carbon emissions were eliminated, sea levels would continue to rise in response to warming that has already occurred. Floods and other extreme weather events will intensify in coming decades, and the only option to mitigate them is to reduce emissions immediately. For this, reducing use of fossil fuels and increasing production of renewable energy. And for that, the most important thing is to get a stronger commitment from all the governments of the world to fulfill the Paris Agreement goals and to implement necessary plans for all governments to develop their marine ecosystems.
UNESCO is leading the UN Decade of Ocean Science for Sustainable Development from 2021 to 2030. Since beginning of the decade, more than 500 projects have been launched in different regions of the world and more than one billion dollars have been raised to develop knowledge and protect oceans that are insufficient to protect and conserve the oceans. It is very important to support the significant GHG emitters and developed countries to reduce emissions as well as to support developing countries through UNESCO to take necessary steps to stabilize the ocean ecosystem.
Dr. M Monir Uddin is an agronomist and consultant GAIN Bangladesh
