Pre-print, Working paper: The paper starts from a proposition of institutional design for climate policies made previously by David Bradford and labelled GPGP (Global Public good Purchase). The scheme is compared with other possible post- Kyoto schemes that are, or not, "Kyoto compatible". The comparison puts the emphasis on the participation issue, (free riding, ratchet effect), and on the desirable flexibility of the schemes. It argues that the incidence of climate policies on the final price of fossil fuels is a key and difficult issue which has not received, untill now, the amount of required attention.