This potentially-revolutionary method of making fertilizer that almost completely removes greenhouse gas emissions has received a grant from Bloomberg Philanthropies to be incorporated into 7 major cities' landscaping programs.

Making "biochar" as it's called, has been modernized recently in Sweden, and is done by putting grass trimmings, hedge clippings, tree branches, or any other kind of yard waste, into an enclosed space and "pyrolyzing it" in such a way as to avoid the rapid oxidation of CO2.