James Hansen has an opinion piece in the Guardian.
Hansen gets to the point.
Stabilising climate requires restoring our planet's energy balance. The physics is straightforward. The effect of increasing carbon dioxide on Earth's energy imbalance is confirmed by precise measurements of ocean heat gain. The principal implication is defined by the geophysics, by the size of fossil fuel reservoirs. Simply put, there is a limit on how much carbon dioxide we can pour into the atmosphere. We cannot burn all fossil fuels. Specifically, we must (1) phase out coal use rapidly, (2) leave tar sands in the ground, and (3) not go after the last drops of oil.
Hansen favours a carbon 'tax and dividend'.
A carbon fee is the only realistic path to global action. China and India will not accept caps, but they need a carbon fee to spur clean energy and avoid fossil fuel addiction.
Hansen has no time for emissions trading.
Governments today, instead, talk of "cap-and-trade with offsets", a system rigged by big banks and fossil fuel interests. Cap-and-trade invites corruption. Worse, it is ineffectual, assuring continued fossil fuel addiction to the last drop and environmental catastrophe.