Don: Time to go again to the A Moment of Science mailbag. A listener writes:

     Dear Don & Yaël,
     I've been reading a lot about climate lately, and I know that the earth stores lots of      carbon in different places, like in the ocean and in plants. Are there any other major      carbon stores?

Yaël: Great question. And the answer might surprise you. While plants and oceans do      store a lot of carbon, much of the planet's carbon is stored in soil. When forests and      crops and other plants absorb carbon dioxide from the atmosphere, they channel      most of it into the soil.

D: Hmm...So I guess the next question is, does global warming have any affect on this      soil-carbon-capture system?

Y: Actually, it does. When soil warms, the microorganisms in it grow feistier and eat      more of the carbon stored in soil. When all those millions of tiny organisms aspirate,      or breathe, they release that carbon back into the atmosphere in the form of carbon      dioxide...

D: Which is the main greenhouse gas that causes global warming. So warming soil      creates a sort of global warming feedback loop-- the warmer soil gets, the more      CO2 it releases.

Y: Right. But there are things we can do to stop or at least slow the process. For      example, farmers could increase the amount of carbon stored in soil by planting more      cover crops, like legumes, that protect and enrich soil between harvests. Farmers      can also do less tilling, because stirring up soil riles its microorganisms and makes      them consume more carbon. So keeping more carbon in soil is good for the      atmosphere, and good for the soil.

D: So it's a win-win.

Y: Right.  

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