1As we saw in the last lecture,
2a major cause of climate change is the rapid rise in the level of carbon dioxide in the atmosphere over the last century.
3If we could reduce the amount of CO2,
4perhaps the rate of climate change could also be slowed down.
5One potential method involves enhancing the role of the soil that plants grow in,
6with regard to absorbing CO2.
7Rattan Lal, a soil scientist from Ohio State University, in the USA,
8claims that the world's agricultural soils could potentially absorb 13% of the carbon dioxide in the atmosphere -
9the equivalent of the amount released in the last 30 years.
10And research is going on into how this might be achieved.
11Lal first came to the idea that soil might be valuable in this way not through an interest in climate change,
12but rather out of concern for the land itself and the people dependent on it.
13Carbon-rich soil is dark, crumbly and fertile, and retains some water.
14But erosion can occur if soil is dry,
15which is a likely effect if it contains inadequate amounts of carbon.
16Erosion is of course bad for people trying to grow crops or breed animals on that terrain.
17In the 1970s and '80s,
18Lal was studying soils in Africa so devoid of organic matter
19that the ground had become extremely hard, like cement.
20There he met a pioneer in the study of global warming,
21who suggested that carbon from the soil had moved into the atmosphere.
22This is now looking increasingly likely.
23Let me explain.
24For millions of years, carbon dioxide levels in the atmosphere have been regulated, in part,
25by a natural partnership between plants and microbes - tiny organisms in the soil.
26Plants absorb CO2 from the air
27and transform it into sugars and other carbon-based substances.
28While a proportion of these carbon products remain in the plant,
29some transfer from the roots to fungi and soil microbes,
30which store the carbon in the soil.
31The invention of agriculture some 10,000 years ago
32disrupted these ancient soil-building processes
33and led to the loss of carbon from the soil.
34When humans started draining the natural topsoil, and ploughing it up for planting,
35they exposed the buried carbon to oxygen.
36This created carbon dioxide and released it into the air.
37And in some places,
38grazing by domesticated animals has removed all vegetation, releasing carbon into the air.
39Tons of carbon have been stripped from the world's soils - where it's needed -
40and pumped into the atmosphere.
41So what can be done?
42Researchers are now coming up with evidence that even modest changes to farming
43can significantly help to reduce the amount of carbon in the atmosphere.
44Some growers have already started using an approach known as regenerative agriculture.
45This aims to boost the fertility of soil and keep it moist through established practices.
46These include keeping fields planted all year round,
47and increasing the variety of plants being grown.
48Strategies like these can significantly increase the amount of carbon stored in the soil,
49so agricultural researchers are now building a case for their use in combating climate change.
50One American investigation into the potential for storing CO2 on agricultural lands is taking place in California.
51Soil scientist Whendee Silver of the University of California, Berkeley,
52is conducting a first-of-its-kind study on a large cattle farm in the state.
53She and her students are testing the effects on carbon storage of the compost that is created from waste -
54both agricultural, including manure and cornstalks,
55and waste produced in gardens, such as leaves, branches, and lawn trimmings.
56In Australia, soil ecologist Christine Jones is testing another promising soil-enrichment strategy.
57Jones and 12 farmers are working to build up soil carbon by cultivating grasses that stay green all year round.
58Like composting, the approach has already been proved experimentally;
59Jones now hopes to show that it can be applied on working farms
60and that the resulting carbon capture can be accurately measured.
61It's hoped in the future that projects such as these
62will demonstrate the role that farmers and other land managers can play in reducing the harmful effects of greenhouse gases.
63For example, in countries like the United States,
64where most farming operations use large applications of fertiliser,
65changing such long-standing habits will require a change of system.
66Rattan Lal argues that farmers should receive payment not just for the corn or beef they produce
67but also for the carbon they can store in their soil.
68Another study being..