In a 2-minute ad spot, the company pitches its formula to fight obesity: Choose products with low or even zero-calorie content, including a broad array of low-calorie drinks from its own portfolio ( Coming Together).
Mr Varian argues that this overcomes the free-rider problem, a particular pain for makers of online content because it can often be reproduced at zero cost.
Lehmann, the lead author of the paper which is published in the journal Nature Geosciences, said that the black carbon content of soils in the study ranged from zero to 82 percent of soil organic carbon.