STEVE INSKEEP, HOST:

Yesterday on this program we followed up on California's own strategy on climate change. Rather than waiting for global action, California passed its own law. The state begins enforcing it in just over a year. It is supposed to limit emissions of greenhouse gases from factories, power plants, and eventually vehicles. Already businesses are looking for ways to reduce their emissions, and NPR's Christopher Joyce reports that one option could be growing weeds.

CHRISTOPHER JOYCE, BYLINE: Let's say you run a power plant in California. You can reduce your emissions footprint by buying new, cleaner equipment. But that can be expensive. So instead, you can help pay to protect a growing forest, for example, because it sucks carbon dioxide out of the air. Or you can pay a farmer to capture methane from a pond of pig waste.

The market for these so-called greenhouse gas offsets is growing already, and lots of people are angling to come up with new kinds of them.

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JOYCE: One potential bumper crop lies in the state's huge agricultural heartland - the San Joaquin Valley.

WHENDEE SILVER: And what we found was that this area was a really big source of greenhouse gases.

JOYCE: When biologist Whendee Silver walks through the valley, she sees something that most people don't notice: greenhouse gases coming up out of the peat-rich soil - carbon dioxide, nitrous oxide and methane. At the University of California at Berkeley, Silver studies ways to reduce those gases. That could create offsets that farmers and ranchers could sell to businesses trying to reduce their carbon footprint. One way to cork up those gases is to flood the peat land and grow a tall grass called tule. Silver and Berkeley environmental scientist Dennis Baldocchi take me to see a field of densely packed reeds about 12 feet high, swaying in the wind. Over centuries, this stuff breaks down into peat soil.

DENNIS BALDOCCHI: These things have grown in this region for about 10,000 years or so. You can stick your hand down if you want to feel the stuff, you can actually...

JOYCE: I'll let you do that.

BALDOCCHI: Okay. Undecomposed (unintelligible). Here we go. This is the stuff that will form the soils that are now being lost as this land is being drained.

SILVER: Smell it. Do you smell the sulfur? That tells you that the air is gone. So take a good sniff. It smells like rotten eggs.

JOYCE: The flooded soil means there's very little oxygen down there. That keeps bacteria from chewing carbon out of the plants and soil and sending it up into the atmosphere. And as the reeds grow - and they grow fast - they suck carbon out of the atmosphere like a big sponge.

SILVER: It's pretty clear when you can see this beautiful green swath of wetland growing next to the brown hills at this time of year, you can see, this is carbon.

JOYCE: Flooding would return the land to the way it used to be. But that would reduce acreage for farmers and ranchers. If they can get paid enough for the greenhouse gases they capture, though, it could be profitable for them. And local rice farmers are interested as well. They flood land to grow rice, and that could capture greenhouse gases too.

BALDOCCHI: Here we may have a small area, but it's a very, very intense carbon sink, and that's the strength of this project.

JOYCE: But there are kinks to work out. For example, flooding land may reduce carbon and nitrous oxide emissions but increase methane.

SILVER: So that's part of the reason we're looking at this, is how much methane comes out, how much carbon gets stored in, and is it sustainable. Can we keep that positive balance of carbon coming in?

JOYCE: Silver calls this carbon ranching, an alternative to expensive retrofits at factories. Derik Broekhoff is with Climate Action Reserve, which ensures that these offsets actually do what they're supposed to do: lower emissions.

DERIK BROEKHOFF: A lot of these emission reductions you can do that a lot more cheaply and so it reduces the overall cost.

JOYCE: California officials are interested in carbon ranching, not least because the state government needs to reduce emissions from its own facilities and vehicles. And it owns plenty of land in the delta. Christopher Joyce, NPR News.

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