Edited to add: That's roughly 60 tons of CO2 emissions per BTC mined. https://www.eia.gov/tools/faqs/faq.php?id=74&t=11
The other aspect here is let's say you're a speculator and you think the price of BTC can go up another 50x or roughly $1M/BTC. Then even spending any amount less than the BTC spot price now is a bargain.
The same can be said for Ethereum. The shortage of GPUs is preventing the difficulty to raise fast enough. The profit margin has been like 5-10x the electricity cost for the last few months. If you bought a RTX 3080/3090 it would have paid itself and the electricity by now.
Speculation > silicon constrained mining > power & capital constrained mining
I believe the silicon constraints would instantly relax as soon as speculation falls into line based on how much hardware everyone has been stacking up on lately.
At the end of they day, the cost of energy & your ability to keep the machines operational will be the final constraint. This is the one that the long investors should anticipate. I.e. "How do I mitigate power cost in a power-cost-constrained market".
Right now at current market prices, owning an entire power plant to run your operation is folly. In a few more years when a delta of 2c/KWh is make-or-break on profitability, it makes perfect sense.
Surely this cannot last. This kind of outsize profit ought to be bringing online enough new mining capacity to increase the block difficulty until that margin erodes away - is it the worldwide chip shortage preventing that from happening?