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Give carbon a decent burial
17 July 2004
From New Scientist Print Edition.
Frederic Hauge and Marius Holm

Sweeping things under the carpet can be a bad idea. But what do you do when the floor is so thick with dust that any reduction would be an improvement? Swap dust on the floor for carbon dioxide in the air, and the carpet for the seabed, and that's a dilemma world governments now face.

In other words, as an interim measure until renewable energy replaces fossil fuels, should we start soaking up CO₂ from fossil-fuel power stations, the largest producers of CO₂, and bury it where it can't contribute to global warming? Given that the alternative means allowing climate change to accelerate, we say that the answer must surely be yes.

Some environmentalists oppose the idea. Greenpeace argues that the sea should never be treated as a dumping ground, that burying CO₂ merely hands the problem of excess on to future generations, and if the gas were to escape it could pose a serious environmental problem in the future. Viewing burial as a solution to CO₂, they argue, also diverts funds and political attention away from dealing with the root of the problem: our continuing dependence on fossil fuels. Green groups also worry that leaks from such burial sites could damage marine life.

Though these concerns are honourable, we are convinced they are misplaced. Tests to date indicate that there is little chance the gas would ever leak or escape. Natural hydrocarbons have stayed trapped in sedimentary basins for millions of years, and if storage sites are selected carefully they could reasonably be expected to retain CO₂ over a geological timescale. For example, in the Pisgah anticline north-east of Jackson Dome, Mississippi, 200 million tonnes of CO₂ is thought to have been trapped underground for over 65 million years.

In the North Sea, the Norwegian oil company Statoil is already burying CO₂. Natural gas from the Sleipner offshore field contains more CO₂ than is allowed in the gas distribution system, so Statoil has to separate out the excess. Instead of releasing it into the atmosphere, Statoil pumps it back offshore where it is injected into the saline Utsira aquifer 1000 metres below the seabed, under a layer of impermeable shale. Since the process began in 1996, about 1 million tonnes of CO₂ have been injected into the reservoir every year, equivalent to 3 per cent of Norway's CO₂ emissions. The alternative would also have cost Statoil dear in CO₂ emission taxes.

A seismic survey in 2002 by the British Geological Survey showed that the CO₂ was forming a bubble 1700 metres in diameter at the top of the sandstone layer, and was not leaking back to the seabed.

This year, Statoil began burying CO₂ at a second gas field, Snohvit, in the Barents Sea. In total, 700,000 tonnes will be stored annually at the deeper site, 2600 metres beneath the seabed.

We need more large-scale test burial sites to learn how to expand the activity globally. But the signs are encouraging.

In the US, natural gas is stored underground in 470 sites. There have only been nine known significant leakage incidents from these sites, all of which were quickly contained. Storing CO₂ rather than natural gas should pose even fewer problems, as there would be none of the cyclic changes in pressure and stress on the surrounding rock that occur when natural gas is pumped in for storage, and then removed for consumption.

Even if in 100 years' time CO₂ did escape from these burial sites, the delayed release would be better than it being added to the atmosphere now. We hope that global CO₂ emissions will be dramatically cut, so an accidental release in the future would not pose as much of a problem as it does today.

Our ultimate aim must be to replace fossil fuels with renewable energy sources. One way in which that can be done is to use hydrogen instead of petroleum-based fuels for our cars and trucks. But where will that hydrogen come from? To replace the fossil fuel expected to be consumed annually by Europe's transport system in 2030 with hydrogen manufactured by electrolysing water would require 3500 terawatt-hours of electricity.

The International Energy Agency's most optimistic predictions estimate a mere 750 terawatt hours of electricity will be produced from renewable sources by then. To close the gap, an extra 65,000 1-megawatt wind generators would have to be installed every year - an ambitious goal to say the least. Add to this the 60 per cent reduction in CO₂ emissions by 2100 that the UN's Intergovernmental Panel on Climate Change says is needed to avoid a climate catastrophe and it's clear action is needed now.

In the long term the plants producing this electricity should run off renewable fuels, but for the foreseeable future they are going to burn fossil fuel. We must reduce greenhouse gas emissions to an acceptable level, sooner rather than later, and that means burying the CO₂ these stations produce. Sometimes sweeping things under the carpet is the only sensible choice.

Frederic Hauge is president of the Bellona Foundation, an environmental campaigning group based in Oslo, Norway. Marius Holm is programme manager at Bellona

From issue 2456 of New Scientist magazine, 17 July 2004, page 16

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