'Cut not sink' emissions, says expert

We would be better off reducing our greenhouse emissions rather than trying to sink them into the sea using ocean fertilisation, suggests an Australian expert.

The comments come as the Australian Government considers its position on ocean fertilisation.

"If you asked me would I do this for CO2 mitigation [I'd say] not now," says Associate Professor Thomas Trull of the Antarctic Climate and Ecosystems Cooperative Research Centre in Hobart.

He says he does not think the benefits outweigh the risks of the technology at this point, and it should only be carefully researched as an option of last resort.

"Imagine if we started to realise that we were actually headed towards melting Greenland or we were going to flood Singapore, then we might say okay, I guess we'd better do this," says Trull.

"Personally I think we should avoid that by acting now on reducing our emissions rather than ... hoping that these backstop technologies will save us later."
Potential benefits

Ocean fertilisation involves adding nutrients such as iron or nitrogen to the sea to stimulate phytoplankton in the hope of sequestering carbon dioxide or fish stocks.

Trull says assuming the technology works and it is possible to verify sequestration, scientific models show the maximum amount of carbon that could be sunk into the ocean is less than 15% of the world's annual human generated greenhouse emissions.

"The total capacity is about 1 Gigatonne of carbon a year," he says.

Trull says the length of time carbon could be sequestered will vary between 6 months and 100 years.
Potential risks

According to Trull no studies have been specifically designed to look at the risks of ocean fertilisation but evidence suggests possible risks include upsetting the food web and creating dead zones in the ocean.

Risks could also include producing worse greenhouse gases like nitrous oxide and methane, blocking penetration of sunlight, trapping more heat or changing ocean circulation, he says.

He says using nitrogen is "more risky" than using iron, because it stays in the system for millennia, compared to iron, which sinks into sediments by natural processes over decades or a century at most.

"For me the overall return isn't that large for something you're taking a risk on," says Trull.

"It does seem to me it's not a huge ask to reduce CO2 production by 15% by reducing the spendthrift ways in which we use energy."
Environmental Assessment

International negotiations are yet to decide on how to control ocean fertilisation, but a number of commercial companies are already carrying out research and development on the technology.

One such company is the US-based Climos, which Trull says is planning to meet with him and other scientists in Hobart next week to discuss testing ocean fertilisation in the Southern Ocean.

The Southern Ocean is ripe for fertilisation with iron, which is the main nutrient limiting further production of biomass there, says Trull

He says Australian-based company Ocean Nourishment Company will be in Hobart the following week.

Trull says it's important for any regulation of ocean fertilisation to take a big picture view of its impacts.

"Many scientists, and I'm certainly one of them, feel that the real question now is what the long-term impact is if you do this in a persistent fashion," he says.

Any one particular project may not pose a problem but he says each approval sets a precedent for others but does not deal with the problem of cumulative impacts over the long term.

"It's a tragedy of the commons problem. We don't really have effective communal legislation to deal with that," he says.

Trull has contributed to a report that will soon be presented to the Australian government on the science and policy options relevant to ocean fertilisation.