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UNSW : UNSW Atmosphere Study Guide
Atmosphere Study Guide 31 While the price tag for this technique would be relatively cheap - photosynthesis is free, and burying the wood would cost about US$14 per tonne - the environmental toll could be substantial. To sequester five billion tonnes of carbon a year, 10 million such trenches would need to be dug and filled. That’s one every three seconds. BLOOMIN’ MARVELLOUS In certain parts of the oceans, especially along the western coasts of large continents, nutrient-rich waters fuel the growth of algae and other phytoplankton. Their growth pulls CO2 from the atmosphere. Many parts of the ocean, however, lack one or more vital nutrients, particularly dissolved iron, and are therefore nearly devoid of life. Adding iron to the surface waters in some seas could help reduce CO2 build-up in the atmosphere and forestall climate change, some scientists suggest. Or maybe not. Recent studies in the North Atlantic and North Pacific confirm that natural algal blooms can indeed sequester CO2, but in many cases the phenomenon may be only temporary, with little if any carbon making its way into deep water or seafloor sediments. In late 2004 and early 2005, a similar study near the Crozet Islands southeast of South Africa further demonstrated that natural algal blooms result in only modest carbon sequestration. Many uncertainties remain about how effective any artificial attempts to boost algal growth might be, says Statham. First of all, he notes, scientists aren’t sure which forms of iron are the ones that marine phytoplankton find most nutritious. And the long-term effects of adding the wrong type of iron - and maybe even the right type - could damage marine ecosystems for years. “There’s a huge gap in our understanding of these phenomena.” SOAK IT UP Today, coal and petroleum each account for about 40% of global CO2 emissions. Of the two, however, coal poses by far the larger threat to future climate. Coal produces more CO2 per unit of energy than any other fossil fuel - burning natural gas only generates 60% of the CO2 emissions, for example. Also, coal is abundant and therefore relatively cheap. Worldwide, coal-fired power plants each Explain (article three) Adding iron to some seas could help reduce CO2 build-up. WIKIMEDIA An algae bloom off the southern coast of England in 1999 year generate about eight billion tonnes of CO2, an amount that contains about 2.2 billion tonnes of carbon. And, says Daniel Schrag, a geochemist at Harvard University in Cambridge, Massachusetts, emissions are poised to get even worse: more coal-fuelled power plants are planned for the U.S . and China opens one such plant every week or so. Because coal-fired power plants are point sources of immense volumes of CO2, they’re tempting targets for sequestration efforts, says Tom Feeley, an environmental scientist at the U.S. National Energy Technology Laboratory in Pittsburgh, Pennsylvania. He and his colleagues are studying ways to capture emissions, ranging from using CO2 -hungry materials to sop the gas from smokestacks to building new plants that burn coal differently. The active materials could either absorb CO2 like a sponge, or chemically bind to it. STORAGE SOLUTION Capturing vast amounts of power plant emissions is just half the task. The next step is storage. Many scientists propose locking CO2 underground or in the deep ocean. Under high pressure - as found at ocean depths below 500 m - CO2 is a dense liquid, not a gas, and doesn’t mix well with water. Therefore it is possible to deposit CO2 on the ocean floor. However, many researchers have concerns about how large pools of concentrated CO2 might affect ecosystems there. The CO2 might slowly dissolve into the surrounding water, creating acidic conditions. Immense volumes of subterranean strata are another tempting dumping ground. Some types of rock formations are naturally impervious to the flow of gases and liquids and have, in fact, already proven themselves by sequestering naturally formed CO2 for millions of years. Oil companies have been mining that CO2 , transporting it through pipelines and pumping it into the ground to enhance the recovery of petroleum from faltering oil fields for decades - an irony indeed to think that CO2 is being pumped into the ground so that petroleum, a raw material for even more CO2, can be extracted. In many parts of the world, saline aquifers lie deep beneath the ground. Because that salty water isn’t suitable for drinking, some of those strata, especially those sandwiched between or capped by impervious rocks, could be used to store CO2. Disposal of CO2 in ancient volcanic rocks may provide an even more secure sequestration technique. The world needs carbon sequestration, says Schrag - and soon, on an enormous scale. The challenge, he notes, is to ensure that carbon capture technologies are ready when political action on climate change is finally taken. And according to King, that time is looming. “It’s beginning to dawn on people,” he says, “that they can change the planet in ways larger than the planet can change itself.” – Sid Perkins