The period 2010 to 2025 corresponds to the period where major reductions in the cost of renewable technologies for electricity generation such as solar PV, geothermal, and wind are expected. While not infeasible, such an amount is clearly very high and not currendy in the range of discussion of what developed countries might be willing to commit without hard negotiations. On the other hand, it is highly plausible that not all countries would be able to reach the threshold we have used for our calculations by 2025, so that the subsidy that would need to be actually disbursed would be lower. However, many other issues would probably arise in the implementation process.