The health of our oceans

By Mike Sparrow

Public debate about climate change has increased dramatically over recent months, with media prominence given to young activists like Greta Thunberg and mass demonstrations orchestrated by Extinction Rebellion. Commentary often focuses upon greenhouse gas emissions and their impact upon global weather systems, with less attention being paid to the health of our oceans.

Like rainforests, oceans play a major role in stabilising the carbon dioxide saturation of our atmosphere, absorbing around a quarter of all CO2. But, despite their huge scale, the delicate balance of our ocean ecosystem is now under potentially devastating strain. 

Here are some sobering bits of information:

• A recent UN commissioned study states that more than 80% of ocean pollution arises from land based human activity.
• More than 8 million tonnes of plastic is estimated to enter the ocean every year and there is evidence that this is ingested by every form of organism; from molluscs to fish, birds and mammals. We now regularly consume plastic in our diets as a result. 
• There are five major concentrations of garbage in our oceans, and although these break up and reform subject to the influence of currents and gyres, the Great Pacific Garbage Patch (GPGP) is consistently regarded as being the largest. One study by Ocean Clean-up, an NGO that is committed to clearing the GPGP, estimates that the centre of the patch is roughly the size of the state of Texas, while the whole patch extends to an area the size of India.
• Up to 90% of ocean plastic pollution may emanate from only 20 rivers.
• There are now more than 500 dead zones in our oceans. The largest is at the mouth of the Mississippi River and extends to an area the size of the state of North Carolina. Devoid of oxygen, nothing lives in these areas, which are substantially caused by pollution from run-off of agricultural pesticides and fertilisers. A report by the Smithsonian Environmental Research Centre suggests that ocean dead zones have quadrupled in the last sixty years.
• 8% of the world’s oceans are now thought to be affected by hypoxia (low oxygen levels), and the problem is expanding horizontally and vertically, affecting habitat for marine life. Areas of low oxygen have increased by 4.5 million square kilometres in the last 50 years.
• The Global Oxygen Network reports that progressive hypoxic conditions have been measured in the Pacific Ocean covering an area the size of South America.
• Oceans absorb more than 90% of the heat trapped by greenhouse gases and surface temperature has increased by 1.5 degrees since the pre-industrial period. Warmer water holds less oxygen, which compromises habitat for many marine species. 
• A 2015 Living Blue Planet report quotes research that indicates that fish populations have decreased by 49% since 1970, with populations of food fishes having decreased by up to 90% due to overfishing and pollution of coastal waters. 

So, while we hear much about the impact of global warming on our weather systems, we should also be paying much more attention to the water that covers two thirds of the surface of our planet, and which currently supports a large part of our global food supply, employment and economy.