Sunday 11 March, 2001
Greenhouse Gas Burial
All over the world scientists and engineers are developing ways to reduce the greenhouse effect. Warm World examines the projects fighting the problem and meets the engineers who are trying to bury greenhouse gases, plant experts who believe the carbon can be sequestered in forests, and oceanographers who are persuading the seas to take up unwanted gases.
Sequestration
Wherever you look in the world today you find signs that our climate is changing. According to the latest report of the Intergovernmental Panel on Climate Change (IPCC), global temperatures have risen by half a degree in the past century, partly because of the greenhouse gases humans are putting into the atmosphere; the IPCC is predicting warming of up to another six degrees over the next 100 years, unless we change our habits. Meanwhile, mountain glaciers are in retreat, sea ice cover is being reduced, storms seem to be more frequent, and climate events like El Nino appear to be getting stronger.
Scientists and engineers have been inventive in coming up with technological fixes for global warming - but will any of them work? And if they will, do they pose long-term dangers for natural ecosystems and so, in the end, for humanity too?
The simplest fix of all would be to stop producing such vast quantities of greenhouse gases, carbon dioxide, methane and so on, which cause global warming. But if that can't be done - and signs are that we will not quit our fossil fuel habit without a fight - then maybe we can store these gases somewhere other than the atmosphere, or find ways of absorbing them from the air - sequestration, as it's known.
Fertilising The Ocean
Fertilising the ocean is a possibility. By seeding the ocean surface with iron, phytoplankton plants could made to flourish and, as they grow, absorb the CO2 that is dissolved in the water; the newly depleted water should in turn draw the CO2 from the air. Last year an international team of scientists took to the stormy Southern Ocean, around Antarctica, and showed iron fertilisation does create a bloom there. But even under the most optimistic scenarios, it would take fertilising the entire Southern Ocean to extract even a fifth of the CO2 we put into the atmosphere.
Other scientists have thought about pumping CO2 directly to the bottom of the ocean. At deep-sea pressures, CO2 is a liquid, and once on the sea floor would sit there indefinitely, and slowly dissolve into the water. However in altering the make-up of the seabed scientists must consider other life forms. Putting more CO2 into the water may also do nasty things to some of the creatures living there. For one thing, it can make the water more acidic. Deep-sea experiments have also shown that the liquid CO2 can knock creatures out.
Underground Reservoirs
The alternative to burying CO2 under the sea is to put it under more solid ground; ground that perhaps could help put a real lid on the CO2 problem. Whilst some scientists argue that the technology to store CO2 underground has been with us for several decades, others believe that what has been missing is the motive.
Under the floor of the North Sea, off the coast of Norway, carbon sequestration has already started. For five years now the Norwegian State Oil and Gas Company, Statoil, has been injecting CO2 into an aquifer, a void in the rock currently filled with water.
The motive was simple - finance. Norway has a carbon tax - companies which emit the gas have to pay for the privilege - and the natural gas which Statoil is extracting from the Sleipner field contains almost 10% CO2. The company had a choice - release this into the air and pay the tax or sequester it. They chose the latter, proving that carbon taxes can make a difference to the businesses they act on.
Statoil draw out their natural gas, extract the CO2, and pump it through a pipe over four kilometres long into the bottom of the water-and sand filled void. That far down it's a liquid, which means it takes up much less space than it would as a gas.
The project started in 1996 and is the only one of it's kind in the world. The Statoil project is now storing a million tonnes a year - roughly 3% of Norway's annual emissions. Experts believe the aquifer is so vast, it could comfortably take all Europe's power-station emissions - a billion tonnes a year - for 600 years before it was full.
| 'Signs are that we will not quit our fossil fuel habit without a fight.' | |
Drawbacks Of Underground Storage
Nothing comes free, and the biggest expenditure in these burial schemes is the cost of extraction - separating the CO2 from the other gases. Although so-called carbon-capture technologies exist, they are currently so pricey that burial schemes solely for protecting the environment: Statoil has to extract the CO2 from its natural gas, even if it didn't bury it, just to make their product marketable.
However, scientists are working hard on new technologies that should make carbon capture more affordable. New approaches such as using membranes, porous fibres, to entice the CO2 out of the gas stream are being tested; other researchers are turning to nature for inspiration by introducing CO2-eating algae into the smoke stacks of power stations.
Long Term Storage
Putting CO2 into deep reservoirs can only help if it stays there for geologically meaningful times … at least until we stop burning the fossil fuels that make the CO2 in the first place, or even until the next ice age some experts suggest. That could be tens of thousands of years away. Apart from a few natural examples of CO2 locked away in deep reservoirs, we have no proof that the new stores could do that. And as one sequestration researcher has put it … wouldn't having CO2 stored away beneath their homes make many people nervous in these environmentally sensitive times?
Another burial alternative has a different kind of drawback. Oil companies are pumping CO2 into half-exhausted oil fields, to force the final reserves out. Although the carbon dioxide flush remains trapped, the extra oil that is brought up will only be burnt up to make more, which would undo the good work for some campaigners.
Reducing emissions in the first place is probably the safest way to tackle the problem of greenhouse gases, but in the opinion of some climate researchers, current attitudes would only allow for marginal savings that way. Until attitudes change, and radical new carbon-free technologies mature, such scientists argue that sequestration does have a role to play. And if you think that the negative outweighs the positive and that the effort going into sequestration research should go into other avenues, ask yourself - what are the real alternatives?
To comment on or ask any questions about the issues raised in Warm World, email the programme makers here.
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| What Is The Greenhouse Effect? |
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Gases such as carbon dioxide, methane and chlorofluorocarbons (CFCs) trap outgoing long-wave radiation keeping heat close to the Earth's surface.
Human activity is increasing the concentration of these gases and the result is that the climate system is out of balance as more energy is entering it rather than leaving it.
At present we are putting seven billion tonnes of carbon into the atmosphere in the form of CO2 each year. The most pessimistic estimates predict this could rise to 25 billion tonnes by the end of the century. That is the scale of the problem the world faces. |
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