Natural Sinks Still Sopping Up Carbon

                                                                 Ecosystems haven’t maxed out ability to absorb fossil fuel emissions

Ecosystems haven’t maxed out ability to absorb fossil fuel emissions

Earth’s ecosystems keep soaking up more carbon as greenhouse gases accumulate in the atmosphere, new measurements find.

The research contradicts several recent studies suggesting that “carbon sinks” have reached or passed their capacity. By looking at global measurements of atmospheric carbon dioxide, the new work calculates instead that total sinks have increased roughly in line with rising emissions.

“The sinks have been more than able to keep up with emissions,” said Pieter Tans, an atmospheric scientist at the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory in Boulder, Colo. Tans presented the findings May 15 at an annual conference on global monitoring hosted by the lab.

Careful measurements of atmospheric carbon dioxide taken in the rarefied air atop Mauna Loa, Hawaii, and elsewhere have established that levels of the gas are rising steadily, from 316 parts per million in 1959 to 392 parts per million today. The question is how Earth’s great ecosystems respond to that increase. Forests can suck down carbon dioxide through photosynthesis, whereas oceans take it up proportionally as levels rise in the air.

Previous work has relied on carbon inventories that gather data from multiple sources to try to estimate how much is being put into the atmosphere and how much is being taken out every year. For the new study, Tans and his colleagues went back to basics, choosing 42 marine sites where carbon dioxide levels have been measured for decades.

The researchers then analyzed how much carbon dioxide was in the atmosphere above each of these sites over time. “Less carbon dioxide has remained in the atmosphere, relative to the amount of fossil fuel emissions, today compared to 50 years ago,” Tans said. Even including the effects of land use change, which may alter carbon sinks, produced no measurable trend, he added.

Exactly where the sinks are isn’t clear. One possibility is that forests are regrowing in parts of the world more than scientists had thought, sucking up carbon in the process. Or the oceans may be taking up significantly more carbon than researchers had estimated.

Ralph Keeling, an atmospheric scientist at the Scripps Institution of Oceanography in San Diego, agrees that both land and the oceans aren’t yet done absorbing all the carbon they can. “The land is responding in a big way” to increasing fossil fuel emissions, he says.

Both Keeling and Tans warn that society shouldn’t get complacent just because carbon is still being absorbed. Rising levels of atmospheric greenhouse gases are triggering other planet-wide changes, such as alterations to the oceans’ chemistry. “The situation is bad enough,” Keeling says, “even with the sinks hanging in there.”

Written by Alexandra Witze@ScienceNews.org

 

A Shiny New Pipe Dream

Capturing the carbon dioxide from power stations is not hard. But it is expensive. A new project in Norway aims to make it cheaper

As Helene Boksle, one of Norway’s favourite singers, hit the high notes at the Mongstad oil refinery on May 7th, the wall behind her slid open. It revealed, to the prime minister and other dignitaries present, an enormous tangle of shiny metal pipes. These are part of the world’s largest and newest experimental facility for capturing carbon dioxide.

Such capture is the first part of a three-stage process known as carbon capture and storage (CCS) that many people hope will help deal with the problem of man-made climate change. The other two are piping the captured gas towards a place underground where the rocks will trap it, and then actually trapping it there. If the world is to continue burning fossil fuels while avoiding the consequences, then it will need a lot of CCS. There is no other good way to keep the CO₂ emitted by power stations, and also by processes such as iron- and cement-making, out of the atmosphere. To stop global warming of more than 2°C—a widely agreed safe limit—carbon-dioxide emissions must be halved by 2050. According to the International Energy Agency, an intergovernmental body that monitors these matters, CCS would be the cheapest way to manage about a fifth of that reduction.

To do this, the agency reckons, requires the building of 100 capture facilities by 2020 and 3,000 by 2050. Which is a problem, because at the moment there are only eight, none of which is attached to a power station. Another 28, mostly in North America, are under construction or planned. But some are likely to be cancelled—as happened on May 1st to a project in Alberta. CCS is thus having difficulty reaching escape velocity.

That is not because it is hard. Since 1996, for example, Statoil, Norway’s largest oil company, has captured and stored the CO₂ which forms part of the natural gas extracted from the Sleipner field in the North Sea. Rather, the process consumes a lot of power that would not otherwise have to be generated—which is ironic, and also makes it expensive. 

Hence the need for experiments like those at Mongstad, to try to improve and cheapen it.

Burying bad news

The most common capture technologies involve running the gas to be processed through a solution of amines or ammonium carbonate. These react with CO₂ to form soluble chemicals called carbamates and bicarbonates. The remainder of the exhaust (mostly nitrogen) can then be vented safely to the atmosphere. The carbon-rich solution, meanwhile, is treated in a separate vessel to release its burden of CO₂, which can then be piped away and stored, and the amines or ammonium carbonate thus liberated recycled.

All of which is fine and dandy except that, if rigged to the average coal-fired power station, this process might use a quarter of the energy the plant produces. According to Howard Herzog, a chemical engineer at the Massachusetts Institute of Technology who has made a study of the matter, that implies a cost of between $50 and $100 per tonne of carbon stored. Carbon dioxide can sometimes be sold to oil companies for injection into partially depleted wells, in order to force more petroleum out of them. For that use it fetches at most $40 a tonne. But much CO₂ is not produced near depleted oil wells—and anyway, the price would surely drop if CCS became widespread. In one way or another, then, the technology will need to be subsidised if it is ever to become important.

There was a rush of interest in CCS in the late 2000s, including $3 billion for it in America’s stimulus package of 2009. But many projects are now being cancelled. Either the developers have lost confidence in government commitments to support them or their costs have turned out higher than expected. Mongstad—a billion-dollar development owned jointly by the Norwegian government and three oil companies, Statoil, Shell and Sasol of South Africa—is a rare exception that has actually opened. Hence the hoopla.

The facility itself consists of two capture plants fitted with more than 4,000 instruments to monitor what is going on, and with a total capacity of 80,000 tonnes of carbon a year. These plants are connected to the exhaust flues of the refinery and also to a nearby gas-fired power station. That lets operators experiment with different flow rates and carbon-dioxide concentrations, which can be tweaked to be anything from 3.5% to 14% (roughly equivalent to those from a coal-fired power station).

The operators will also experiment with the capture technology itself. At one of the two plants Aker Clean Carbon, a Norwegian firm, will have 14 months to try out a new amine solution. At the other Alstom, a French concern, has 18 months to test the ammonium-carbonate process.

Amine- and ammonium-carbonate-based CCS are not, however, the only ways to do things. Two other techniques, called gasification and oxy-combustion, work by reacting coal with pure oxygen rather than air, and thus produce exhausts that require little treatment before burial. The former uses coal, oxygen and steam to produce burnable hydrogen. The latter burns coal directly. Purifying oxygen and raising steam, however, both consume energy. And gasification also requires bespoke plants. Unlike the other processes it cannot be retrofitted to existing power stations.

The upshot is that there is no free lunch. If people are serious about carbon capture and storage, they will have to pay for it. The best that facilities like Mongstad can do is make the meal as cheap as possible.

 The Economist