A groundbreaking farm scheme in California has the potential to cancel out the state’s entire commercial and residential carbon emissions – by using waste. A collaboration between scientists and San Francisco’s garbage disposal unit, the scheme turns food and yard waste into compost and spreads it into rangeland, i.e. grassland, pasture, scrub and chaparral. A study by UC Berkeley calculated that covering just 5% of California’s degraded, grazed rangeland with half an inch of compost would remove an amount of carbon roughly equal to the CO2 released in providing the energy used by the state’s homes and businesses in a year.
As the calculation includes carbon drawn down into the rangeland and a reduction in emissions from landfill, it promises to create an elegant, circular economy-style solution to the twin problems of waste and climate change. After eight years of small-scale trials, the scheme, which is part of a wider Marin Carbon Project, is now ready to be tested on whole ranches or batches of government-owned land. ‘If we prove this out in the next two years, you could go for 5%,’ Kevin Drew, San Francisco’s Special Projects Zero Waste Co-ordinator, told Apolitical. ‘It would be a mammoth effort, capturing the food and yard waste currently going to landfills and combining it with manure and trimmings, but that could create a lot of compost, enough to take a shot at the 5%.’
The science is comparatively straightforward: as every gardener knows, compost makes plants grow bigger. Their photosynthesis draws in carbon dioxide from the air and gives out oxygen. The bigger the plants, the more carbon they use. The new news is that applying compost just once kick-starts a cycle of increased carbon sequestration for a period the researchers estimate at 30-100 years. To give a sense of the potential scale of this process, the amount of carbon in the atmosphere worldwide drops 2ppm after every spring. (The global level generally fluctuates around 400ppm and the level considered safe by climatologists is under 350ppm.)
Drawing carbon out of the atmosphere – rather than reducing emissions – is attracting increasing interest as a means of preventing climate change. Norway has given out billions of dollars in subsidies to countries like Brazil to encourage tree planting. And France has launched a campaign to increase the amount of carbon in its soil by 0.4% every year from now on.
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