All the __ in this sentence has been removed and stored below.

(CO2)

That's how one version of carbon sequestration works.

The other is more natural. Circle-of-life stuff that has been happening forever.

Both methods reduce the amount of carbon dioxide that is released to the atmosphere. You hear a lot about carbon sequestration or carbon capture these days, techniques that could mean a great deal for North Dakota in the near future. In addition to reducing emissions - something that could soon be required under federal law - stored CO2 can also help pull more money out of the ground by releasing oil and coal-bed methane that traditional wells can't reach. More on that later.

Right now, let's get to the bottom of what the terms mean and how it all works. Carbon management, which includes the capture and storage of carbon dioxide, is a highly complicated process. But it's pretty easy to understand in theory.

First, you need to know that carbon sequestration basically happens in two ways - direct and indirect.

The direct capture of carbon dioxide usually means grabbing the gas before it leaves its man-made source, like a coal-fired power plant. It's then compressed for storage in underground traps. Bismarck's Basin Electric Power Cooperative owns a coal-gasification plant near Beulah that captures more CO2 than any other single source in the world.

Indirect capture refers to the natural carbon cycle, where corn or switch grass or the wild prairie rose "breathe" in CO2. They exhale the oxygen and keep the carbon to help them grow. This effect can be enhanced by improved land-management practices.

Indirect capture is also known as terrestrial sequestration. Direct capture is often referred to as geologic sequestration.

There is a lot of science behind each method, but if you gloss over that and look at the basics, the steps seem pretty simple.

Geologic sequestration

The idea behind this is pretty new - it's only been practiced in North Dakota for about eight years.

The goal is twofold: First, carbon dioxide is prevented from entering the atmosphere; second, when the gas gets stored underground it can repressurize oil, allowing operators to extract more black gold from what had been a dying oil field.

That's what's happening at Basin's Dakota Gasification Co., which sends nearly 9,000 tons of captured CO2 through a pipeline to Saskatchewan every day. The result is millions of dollars in CO2 sales for DGC and many millions more for EnCana, the oil company that uses the CO2 to enhance its recovery operations by 10,000 barrels a day.

That economic possibility, coupled with environmental concerns about global warming, have spurred the interest in geologic sequestration.

In the last two years, the U.S. Department of Energy has invested $80 million to study sequestration options in a region that includes North Dakota. The recipient of the money, the Plains CO2 Reduction Partnership, has said the geology in North Dakota's oil patch is promising for the large-scale storage of carbon dioxide.

But how will all that work?

Well, the first thing that's needed is the technology to capture carbon dioxide. One of the problems is an apparatus doesn't yet exist that can capture carbon from the largest single source in North America - coal-fired power plants.

What happens at smaller commercial sites, like DGC, is the carbon dioxide gets removed from the waste stream and collected in a contactor tower. It works like blowing air through a straw into a glass of water. The CO2 from your breath goes into the water and makes bubbles. Instead of water in the towers, though, they use different solvents to absorb the gas. It's then compressed so it can move through a pipeline to the point where it will go in the ground. How much the gas is compressed depends on how far underground it's going.

The ideal underground home for carbon dioxide is a natural geologic formation where other carbons get trapped. That's why oil fields and unminable coal beds work so well. There are several layers of traps and seals that prevent the buoyant gas from leaking to the surface. Deep underground saline formations, like those scouted in the Williston Basin, also have the potential to make good storage sites.

While underground, the CO2 dissolves in oil or water, adheres to rock and mineralizes. Some of it can stay in gas form.

Another benefit to geologic sequestration is enhanced recovery of coal-bed methane. The methane molecules like to stick to coal; but coal likes CO2 better. There is only so much surface area on the coal, so when the spots newly taken by CO2 are occupied, the methane must go elsewhere. One other place is up through the methane well. Coal-bed methane is the fastest growing source of natural gas in the country, according to the PCOR project.

Terrestrial sequestration

The chemical symbol for carbon dioxide - CO2 - isn't the only mash of letters you've heard of that's related to carbon sequestration.

Here are a couple of others: CRP and PLOTS.

Land-management programs like the Conservation Reserve Program and Private Land Open to Sportsmen were created in part to return soils and habitat to their natural conditions. One major byproduct of that: Better carbon storage.

Terrestrial sequestration uses plants' natural ability to capture carbon dioxide and convert it to carbon. When plants die or soil is turned over for farming, some of that carbon gets released to the air, where it forms again with oxygen and makes more CO2.

Common practices that can be implemented include no-till farming, rotational grazing, growing buffer strips along waterways and planting cover crops.

The major advantage of terrestrial sequestration is that it can be implemented almost immediately, without waiting for technology to catch up.