  A review of some of the evidence for the IPCC's conclusion that doubling
CO$_2$ levels will warm Earth significantly, in contrast to the claims of a
recent article$^1$. Simply looking at raw temperature and CO$_2$ data over the
past 150 years gives a transient response of roughly 2 K per doubling, in good
agreement with IPCC conclusions based on far more extensive analysis. The 0.58
K of Ref. 1 is very unlikely.
