Is acceptance of the science of global warming by politicians primarily a result of the bandwagon effect?
First off, political agendas in Western democratic countries are, of course, shaped by the masses. 

Secondly, global warming is becoming a science in its own right. Climatology is important and is based on models based on historical data to predict the future, taking into account current greenhouse gas concentrations, melting of the polar caps, sea levels, population growth and what not. In other words, it is far too complicated a subject to be completely understood by the regular ground folks. 

Thus, indeed, [intelligent, capable] politicians rely on scientists to do the thinking for them. In turn, politician's agendas are shaped by the populace so their focus is, and should be guided by the masses.

This should, however, not be a reason to adhere to hypotheses and theories to be correct or incorrect based on the people's opinion. And hence I do not agree that politician's opinions in general are shaped according to the bandwagon appeal.