How Climate Policy Went Wrong

livemint.com:

I chuckle when somebody insists CO2 is a greenhouse gas and that’s all there is to it. Virtually all expert science would say, then, don’t worry about CO2 because the direct effect of increased CO2 is easily calculated to be only about 1 degree Celsius of warming from an expected atmospheric doubling later this century. To make CO2 responsible for the warming already observed—1.2 degrees—scientists have to posit “positive" or warming feedbacks.

In a new paper, veteran NASA scientist James Hansen offers a larger estimate of the (ironically) negative feedback from particulate emissions. This negative feedback (cooling) becomes, in effect, a positive feedback (warming) only because our efforts to curb air pollution allow more sunlight to reach Earth’s surface. In his overall model, 70% of warming comes from positive feedbacks rather than from CO2 directly, slightly more than in some standard models.

These feedbacks start life as exercises in scientific imagination, since they don’t necessarily announce themselves or their magnitude or even direction (warming or cooling). Important feedbacks are believed to include changes in water vapor, darker or lighter clouds, increases in light-absorbing ground cover, decreases in light-reflecting ice, etc. Amid so much scientific guesswork, a blessing is that the recommended policy, a carbon tax, could be implemented in “no regrets" fashion, by cutting other taxes in a way that would stimulate global society’s growth and adaptation overall.