Lots of them.
In fact, the room is so full of elephants, it's hard to move, let alone think clearly.
Here is elephant #1: Over-population.
We can talk all we like about CO2 levels, resource depletion, or the rate of species depletion/extinction, but it will mean zip until we factor into the debate the real impact of over-population, either at the national, regional, or global level.
And it's an elephant for very good reasons: No one (except the Chinese) is game to tackle this issue either as a topic for debate or as a subject for policy-making.
Sticking our heads in the sand will not make this elephant go away...