IMHO, the discrepancy on the effects of pollution are related to whether one
is looking at the problem from a local or global perspective.
Smog in cities is (was) largely due to cars, however, this effect is quite
local. When winds disperse this pollution, it is then insignificant to the
global climate. However, it is significant to the conditions under which
most of us live.
When one is investigating what sources of pollution have a global impact,
cars then become quite minor.
It is important to recognize that many of the other pollution sources are
away from cities (power stations, cows, etc). THese contribute on a global
scale, but don't affect pollution in cities very much.
No warrantees on the accuracy of the above, YMMV, etc.
Simon
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