(Part of the How to Talk to a Global Warming Skeptic guide)
Objection: Scientists claim that global warming from greenhouse
gases is being countered somewhat by global dimming from aerosol
pollution. They even claim that aerosol pollution caused the
cooling in the mid-century. But GHGs are evenly mixed around the
globe, while aerosols are disproportionately concentrated in the
Northern Hemisphere. It follows that warming should be greater
in the Southern Hemisphere — but that’s the opposite of what is
happening. Clearly climate scientists do not know what is really
going on. Answer: Aerosol cooling does indeed affect the
Northern Hemisphere, where most aerosols are produced, more than
the southern hemisphere. It is also true that GHGs are well-
mixed in the atmosphere — apart from a lag of a few years,
southern hemispheric concentrations are rising just the fast as
northern. Where the argument goes wrong is in its assumption
that uniform CO2 concentrations imply uniform heating. It is
completely in line with m