What is the ecological effect of increased work for the Bitcoin chain? As more users use Bitcoin and "forced work" difficulty increases what effect does this have ecologically? It is a silly question I know. I'm just comparing let's say value or effect of using computational power for protein folding vs Bitcoin and curious if anyone has given or found some thought/exploration on the matter.
Blockchain.info reckons the network used    156.51 megawatt hours of electricity in the last 24 hours. This random physics page I googled up reckons a car driving at 40mph takes 100kW (so, 2.4 MWh in 24 hours).

So by these (very) rough figures, running the Bitcoin network takes about as much energy as driving 65 cars.

How many vehicles are used in the transportation of physical cash? Not to mention the energy costs of physically storing and securing cash. I'd say Bitcoin is almost certainly a net positive for the environment to the extent that it displaces physical cash.