Man at B&Q wrote:

The is quite a long list of things that contribute to the variability of
climate. One of these is the CO2 concentration in the atmosphere. This
is now about 50% above the pre industrial level. You might not think
that the huge amount of CO2 resulting from human activity in the recent
past has anything to do with this rise or with climate change but the
great majority of the scientists who investigate such matters do.

So? Were the majority who used to believe in the miasmatic theory of
disease correct?

Methodology in science has come a long way since then.

I'm sure there are plenty of other examples where passionately and
strongly held majority views were eventually shown to be wrong.

Possibly but I can't think of anything like that in the recent past. The
closest I get is the steady state universe versus the big bang which
isn't exactly the recent past these days and in any case was at the
leading edge of cosmology at the time. It often takes time for a new
theory to have its kinks ironed out. The greenhouse effect has been
established fact too long for the basics to be wrong. Where the argument
needs to be is in the extent to which AGW is adding to the underlying
natural variation as that influences what counter measures are needed or
can be effective if taken.

What's different about AGW?

The huge amount of compelling evidence.

For there to have been no AGW you would have to accept either that
mankind had nothing to do with the 50% increase in CO2 concentrations or
that CO2 is not a greenhouse gas.