Though she still thinks we Must Act Now:

Discussions over how to mitigate climate change’s worst effects — which policies we can and should implement — have set off one of the most important and most complex debates to take place in Congress.
Only one idea, a carbon cap-and-trading scheme, has received significant attention on Capitol Hill. And yet, serious doubt has been cast on such a system’s ability to keep energy affordable and our economy strong while still achieving substantive emission reductions. Other policy options — a tax on carbon, massive investment in advancing clean energy technology, even geo-engineering — have largely been ignored.
I recognize that time is short and that action is needed soon. But at what point did we decide cap-and-trade was the most effective way to address climate change? Setting politics aside, are there other approaches capable of achieving the same results at lower cost and with greater regulatory efficiency? Would the debate over climate policy benefit from an attempt to re-evaluate our options?