It's going to be real work for scientists to estimate what the real reductions in greenhouse gases will be with this sort of scheme. In this case, Chile can do the work and Japan can buy its way out. Then there is the problem of things like hydroelectric projects that (as pointed out in the article) were going to go ahead anyway and thus are not replacing any real greenhouse gas production.
Also, modern farms often throw away large parts of their yield without thinking about it. Yes, pigs make manure and pig manure makes natural gas. But chickens produce heat (there is such a thing as a chicken-heated greenhouse) and chicken manure is very rich in phosphates. These are examples of important yields that are usually thrown away.