It is indeed from the mining side, because they keep increasing the work needed for mining. However, I've also come across other sources which figured out that for example a bank in the top 20 of the US uses 10 times more power if you compare what is needed for offices and buildings etc. to the entire international bitcoin network. So it might not be that problematic at all in the end?

Check it out: https://webonanza.com/2015/10/06/is-bitcoin-mining-an-energy-waste-3/