Engineer 'carbon sinks'? Not so fast

Michael Richardson, Straits Times 15 Mar 09;

RUSSIAN and South Korean scientists made a disturbing discovery recently in the Sea of Japan.

They found that the amount of carbon dioxide, the main greenhouse gas, being absorbed in the water dropped by half between 1992 and 2007. They also reported that not as much of the carbon dioxide being absorbed in the Sea of Japan was being held at depths of more than 300m, where it was more likely to stay permanently.

French scientists concluded last month that there had been an even sharper drop in the capacity of the Southern Ocean surrounding Antarctica to soak up the excess carbon dioxide being released into the atmosphere, largely as a result of fossil fuel burning and deforestation.

In its latest report in 2007, the United Nations Intergovernmental Panel on Climate Change estimated that human activity produced 32 billion tonnes of carbon dioxide worldwide each year, but that only 15 billion tonnes actually stayed in the atmosphere and affected climate change. The oceans, forests, vegetation and soil stored the rest.

In this natural system of 'carbon sinks', the oceans - which cover about three-quarters of the earth's surface - played a key role. They were thought to absorb about eight billion tonnes of carbon dioxide, one-quarter of the annual total.

The Southern Ocean was rated as the biggest ocean sink. But scientists affiliated to France's National Centre for Scientific Research now reckon that it may take in ten times less carbon dioxide than previously estimated, around 50 million tonnes annually instead of 500 million tonnes.

The weakening of this carbon absorbing cycle would leave substantially more carbon dioxide in the atmosphere, increasing the pressure on governments to adopt stricter controls on emissions to prevent dangerous rises in temperature.

The French scientists concluded that climate change was affecting atmospheric pressure in the region, causing higher wind speeds in the often stormy Southern Ocean. This caused increased mixing of deep waters with surface waters.

Water near the surface contains less carbon dioxide than deep water. The gas is absorbed by vast numbers of minute algae known as phytoplankton. They not only provide the basic food sustaining

oceanic life, but also help to regulate concentrations of carbon dioxide in the atmosphere. As the organisms die, they sink and get broken down by bacteria, thus enriching the deep water with carbon dioxide and trapping the greenhouse gas.

Some scientists believe it may be possible to absorb in the sea much larger amounts of excess carbon dioxide from the atmosphere by seeding the oceans with iron or other nutrients that make phytoplankton multiply.

A study published in January by researchers at the University of Southampton in Britain looked at a natural source of iron released into the sea near the Crozet Islands in the Southern Ocean, 2,250km south-east of South Africa. It showed that iron - which is added by volcanic rocks to the north, but not to the south, of the island - tripled the growth of phytoplankton and also the amount that sank into the depths of the sea.

Meanwhile, a team of scientists from India, Germany and Chile is on a German polar research vessel in the Southern Ocean, roughly midway between the southern tips of Africa and Latin America. The team is nearing the end of an experiment to fertilise about 300 sq km of sea with up to 20 tonnes of iron sulphate, a relatively minute amount of nutrient.

By the time their ship docks in Chile tomorrow, they will have observed the development and impact of the phytoplankton bloom on the environment and the progress of the carbon sinking to the deep ocean as the algae die.

The experiment is the most comprehensive of six carried out since 2000 by Germany's Alfred Wegener Institute for Polar and Marine Research and India's National Institute of Oceanography. But scientists involved say that based on current knowledge, they oppose large-scale iron fertilisation to regulate the climate.

Fertilising oceans with iron is advocated by those who believe that geo-engineering is a promising way of preventing extensive climate change. Some say it could remove as much as one billion tonnes of carbon dioxide from the air every year if applied widely.

Private companies in the United States and Australia have come up with schemes to seed the oceans with iron and then sell carbon credits to energy-intensive firms that need to offset their emissions by buying the credits. They estimate that ocean iron fertilisation could be worth US$100 billion (S$153 billion) in the carbon trading market.

However, no one knows exactly how much carbon dioxide can be captured and stored in this way, for how long, or the risks to ocean ecosystems. Until these questions can be answered with reasonable certainty, it would be irresponsible to allow geo-engineering ventures to proceed.

The writer is a visiting senior research fellow at the Institute of Southeast Asian Studies in Singapore.