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