Human enterprise has increased by 40 per cent since the Industrial Revolution, which was around 250 years ago. Since then, there has been a great increase in atmospheric concentrations of heat-trapping gases (carbon dioxide, methane and nitrous oxide) which is bringing about irreversible modification of the entire Earth System including the oceans.
The average atmospheric temperature has risen by about 1° C. The temperature increase would have been even more but for the fact that 80 per cent of the extra heat retained by the planet goes into the ocean, increasing its heat content and water temperature.
What the warming doesFirst, thermal expansion of seawater and melting of polar ice will lead to increase in sea levels by as much as 0.8 m by the end of the century. This will cause flooding in many coastal areas, and enormous economic loss.
Increase in cyclones.
Affects ocean currents and mixing.
As marine organisms are not adapted to high sea surface temperatures, warming will cause severe ecological disturbances. About a quarter of all carbon dioxide released into the atmosphere (over 11 trillion tones at present) is absorbed by the ocean, making seawater acidic. This impacts organisms that build calcareous shells as it will be difficult to do so in an acidic ocean. Which will in turn impact oceanic food webs. The coral reef ecosystems that account for 20 per cent of the oceanic biodiversity will be the worst affected.
There will be a loss of oxygen from seawater. Dissolved oxygen levels are decreasing globally in the ocean presumably due to warming. But, the effect is more severe in coastal areas because of the enhanced supply of fertilizer from land which promotes algal growth (eutrophication). Loss of oxygen has led to development of over 600 “dead zones”. As there is no fish, it affects the communities that depend on the sea for a living.
Humans must realise that the oceans do not have unlimited capacity for waste assimilation, and continued unsustainable exploitation of the ocean will severely affect the invaluable ecosystem services they offer. Therefore, on this World Ocean Day we must commit ourselves to ensuring cleanliness of our seas as a healthy ocean is crucial to the wellbeing of mankind.
Space-eye view
When viewed from space, our planet appears blue. This is because 71 per cent of the Earth’s surface is covered by the vast blue oceans that contain as much as 1,338 million cubic kilometres of water. The Earth is the only known celestial body endowed with such enormous quantities of this precious substance. This is because it is of the right size, has the right chemical composition and is located at the right distance from the Sun. These optimal conditions allowed the origin and evolution of life, which in turn led to vast changes in the environment, climate and landscape of our planet.
For example, the oxygen we breathe was absent during the early history of the Earth. It was between 2.5 and 2 billion years ago that microscopic plants evolved that could use solar energy to split water and produce organic matter and oxygen.
Our genus Homo appeared only about 2.5 million years ago, and the sub species of Homo sapiens evolved some 200,000 years back. With the development of human civilisations in the last few thousand years, humans started messing up the Earth’s environment. Eventually, it reached a stage where human activity has become the most important driver of planetary change.
What’s destroying our oceans?
1. Release of industrial effluents in coastal bodies degrading water quality and contaminating seafood.
2. Disposal of untreated municipal sewage to rivers and coastal water bodies. As a result of which, along the Indian coast there has been an increase in disease-causing bacteria.
3. Seasonal deposition of tar balls on beaches along the west coast of India arising from oil spills.
4. Plastics or synthetic polymers do not get degraded easily but break down to micro particles that can absorb persistent organic pollutants, bringing them into the food web.
The writer is the Director, CSIR-National Institute of Oceanography, Goa
Word list
Thermal expansion: The tendency of matter to change in shape, area, and volume in response to a change in temperature.
Calcareous: mostly or partly composed of calcium carbonate
Dead zones: a place or period in which nothing happens or in which no life exists.
Ecological disturbances: a temporary change in environmental conditions that causes a pronounced change in an ecosystem
Irreversible modification: Changes that can never be brought back to normal
