(This is also featured as a guest post on Skeptical Science) The
greatest source of uncertainty in understanding climate change
is arguably due to the role of aerosols and clouds. This
uncertainty offers fertile ground for contrarians to imply that
future global warming will be much less than commonly thought.
However, some (e.g. Lindzen) do so by claiming that aerosol
forcing is overestimated, while others (e.g. the NIPCC) by
claiming that aerosol forcing is underestimated. Even so, they
still arrive at the same conclusion… Let’s have a look at their
respective arguments. Below is a figure showing the radiative
forcing from greenhouse gases and from aerosols, as compared to
pre-industrial times. The solid red curve gives the net forcing
from these two factors. The wide range of possible values is
primarily due to the uncertainty in aerosol forcing (blue dotted
line). The greenhouse gas forcing (dashed red curve) is
relatively well known, but the aerosol forcing (dashed blue
curve) is not. The resulting net a