The world will be switching to renewable source of energy before that happens and coals as source of energy will be gone. With all the talk of climate change, most country will adopt to solar, wind, geothermal or hydro as source of energy. Asics will adopt as well to consume less energy with better output. So i think this is not a problem at all.
There is no doubt that Bitcoin does acquire a lot of electricity intake . Many such concerns regarding the over-exploitation of electricity and energy resources for consumption of electricity to perform Bitcoin mining have been shown in the past . The concerns are not wrong but the give a sense of "plotting" and "degrading" the already controversial image of Bitcoin . In coming years there is going to be a maximum consumption and production of electricity via renewable resource .
Major innovations and developments are being made in order to minimize the cost and energy consumption for the process of Bitcoin . Already the advances of technology has gone from CPU mining to ASICs and cloud mining to resolve and support the issue . I think it would be fair to give them some time to further improve and improvise.