and there's another vital service that trees and plants provide: photosynthesis. vegetation reduces the greenhouse effect by taking carbon dioxide out of the atmosphere. a measure of what restoring nature can do has been shown here on china's loess plateau, where farmers have continued to prosper despite the worst drought in decades. >> [singing] >> since the beginning of the project, the soil that nurtures their crops has been accumulating organic material from plants and animals. this holds the moisture and contains carbon. what's interesting about this is all these root materials, all this other stuff, this is organic material. and this organic material is mixing together with the loess, the geologic soils here, and is making a living soil. this is where the moisture resides. yesterday it rained and there's still moisture in the soil. this is where the nutrients are recycled so that each generation of life emerges here. and this is where the carbon is. what's interesting about this, they made this field, this is new, so they're helping to sequester carbon. livi

since they survive on photosynthesis, they tend to live near sunlight, or in shallow waters. seabeds are diverse ecosystems supporting fish, algae, and yes, oysters. >> so right now this grass below us is actually doing a service. >> it is, it is doing a service. we're finding that it's complicated. >> complicated because of this: when the sun shines, sea grass absorbs carbon, but at night the opposite happens, photosynthesis stops and respiration is dominate, carbon is released back into the water. >> so how do you guys monitor what sea grass beds are actually doing? >> we actually place sensors that measure temperature and salinity and ph and carbon dioxide and oxygen inside the sea grass beds themselves and we let the sensors sit there for weeks at a time and collect data. >> it is still too soon to know what, if any, long-term promise sea grass holds. it may only work in a small, localized estuary like here in tomales bay, but that's a start. >> when i look around here it is beautiful the oysters taste great. but for you it's a bit of laboratory. >> it is a natural labora

they absorb carbon dioxide from the atmosphere, and, through photosynthesis, produce the oxygen we need