Depends on the infrastructure, actually. Some machines are more efficient than others, and therefore consume less energy for the same work. Nobody knows the exact number, but you can make an estimation based on the hash rate and the energy required for the most efficient machine to hash. You can assume every hash is being produced by the most efficient, and figure out what's the least energy consumed for mining.
I keep hearing it is an ‘energy intensive’ industry, but I know for a fact that there are industries that are a lot more polluting than Bitcoin Mining.
The financial sector, first and foremost.