The threat is in the form of increasing global warming which results in climate change. Generating Bitcoin requires a capable computer to solve complex mathematical puzzles and high electricity consumption. so that some countries prohibit mining for several other reasons such as in China and Iran some time ago. if so will bitacoin and others be able to run forever or is this just an excuse to change the green field to red..
According to google 0.55% of total global power consumption are used by mining bitcoins & other cryptocurrency. It will be unfair to put the blame on bitcoin mining alone since its less than 1% of what the world consume. Even if bitcoin mining stops it will not have an immediate effect on lessening the global warming.