Remember carbon capture and storage? Five years ago, the idea of grabbing the carbon dioxide from coal and gas power plants and burying it deep underground was considered an essential technology for curbing the world's greenhouse-gas emissions.

A diagram of how various sorts of carbon capture might work. (Congressional Budget Office)

But carbon capture hasn't fared well in the years since. Since 2008, world governments committed at least $25 billion to fund large-scale demonstration projects, the Financial Times reports. And we have remarkably little to show for it so far.

At the moment, there are only two coal power plants on the horizon that are capable of capturing and sequestering their carbon emissions: The Kemper County plant in Mississippi and the Boundary Dam project in Saskatchewan. Both are slated to open in 2014 and will pump the carbon they capture into nearby oil wells to flush out more crude.

Beyond that? The landscape is thin. A recent report from the Global CCS Institute notes that the number of carbon-capture projects on the drawing board actually declined last year, from 75 to 65. The technology is still expensive — and governments are now shying away. (The FT notes that about $8 billion worth of that $25 billion in financing is being clawed back.)

The case for CCS

The Global CCS Institute argues that carbon capture is indispensable for averting drastic climate change. They cite a recent International Energy Agency report that envisions a major role for carbon capture in cutting emissions enough to avoid 2°C of global warming:

What's more, the report points out that carbon capture is one of the few viable ways to reduce greenhouse gases from cement, iron, steel, chemical and refining plants, which together make up 20 percent of global emissions. "Without [carbon-capture]," the report says, "it is unlikely that the 2°C target is achievable."

The report points out that carbon capture isn't unproven: There are at least 12 large projects worldwide that use the technique. Most of them involve taking carbon-dioxide from gas processing or fertilizer plants and pumping the gas into older oil wells in order to flush out hard-to-reach crude oil, a technique known as "enhanced oil recovery."

The real challenge, however, is adapting this technology for use by power plants, refineries, cement plants and other industrial facilities. That's the ultimate goal — and that extra step remains maddeningly elusive.

The difficult economics of carbon capture

Even if one accepts that carbon capture is a good idea, the economics are daunting. A 2012 report by the Congressional Budget Office estimated that coal-fired power plants that capture and store carbon will initially cost around 75 percent more than regular coal plants. That's mainly because of the extra energy needed to capture and compress the carbon-dioxide.

In the United States, that's a deal-breaker for utilities. Right now, the low cost of natural gas has made it uneconomical to build regular coal plants — let alone ones outfitted with carbon-capture technology.

The big exception, Southern Co.'s $2.4 billion Kemper County plant in Mississippi, was built with the help of a $270 million grant from the Department of Energy and a $133 million tax credit. That plant also has a special funding stream: It will sell some of the carbon it captures for use in enhanced oil recovery to defray costs.

The Kemper County CCS project in Mississippi, slated to open in 2014, though fewer new projects are underway globally. (Mississippi Power)

Yet Southern Co. argues that the Kemper plant is so unique that it's unlikely to be widely duplicated, noting that the facility's "ideal" location allows the carbon to be used by the nearby oil industry. "The unique characteristics that make the project the right choice for Mississippi cannot be consistently replicated on a national level," said spokesman Tim Leljedal in a recent statement.

The Obama administration, for its part, has hinted at providing $8 billion in loan guarantees for low-carbon fossil projects to promote further carbon capture. Yet it's still unclear when this money will materialize. And coal backers note that the Environmental Protection Agency's recent carbon standards for new power plants could make it harder to develop carbon capture, by preventing the industry from working incrementally toward its goal.

Similar funding difficulties are popping up elsewhere in the world. Last month, the Norwegian government pulled back on a plan to capture carbon from the Mongstand oil refinery after sinking $220 million into a project that had gone well over budget. (Norway will continue funding R&D for carbon capture.)

The Global CCS Institute expects more projects to falter unless governments increase their support for the technology — through more funding for R&D and demonstration. "Existing policy support alone is not enough," the report argues, noting that only a handful of smaller carbon-capture projects will be able to support themselves through selling carbon for oil recovery at this point.

Is China the last hope?

The one bright spot for the carbon-capture industry, the report notes, is China: "China now has 12 projects spread across all stages of development planning compared to five in 2010, ranking second to the U.S. China is well positioned to influence the future success of [carbon capture]."

Unlike the rest of the world, China is planning to double its budget for carbon-capture projects, hoping to attract some $380 million in investment over the next five years. As the map above shows, China is planning several coal and gas power plants that can bury their carbon deep underground. And they're partnering with U.S. companies to do so.

For now, China is looking into offsetting the extra cost of these power plants by using the captured carbon to recover oil from nearby wells. The hope is that China could then move to build coal plants that can stash their carbon in vast underground aquifers.

The latter technique would be necessary for carbon capture to ever catch on widely with power plants. (A recent study suggested that the United States had enough space in its underground saline aquifers to store 100 years' worth of coal-plant emissions.) But this is still a ways off.

Further reading:

— A helpful primer on what carbon capture is, how it works, what it can do. There are maps and graphs.

— The CBO has taken a look at why carbon-capture efforts aren't going so well in the United States.

— For those who really want to wonk out, here's a 2010 paper (pdf) from the Energy Department on why CCS that depends on enhanced oil recovery is unlikely to be a good stepping-stone to widespread CCS.