Cryptocurrency energy use

I have been reading about the amount of energy that the cryptocurrency industry uses each year.  One source said that in the US, 25-50 million tons of carbon dioxide are emitted per year from cryptocurrency activity, which is about the same as the emissions from the diesel fuel used by all the railroads in the US.  Other sources say that global cryptocurrency activities use more energy than many countries use.  One cryptocurrency system has developed a protocol that significantly cuts energy use, but it is not clear if other systems will adopt similar protocols. 

In addition, significant amounts of computer hardware are discarded each year as bigger, faster computers are acquired to support cryptocurrency activities.  Significant energy and resources are required to build and then dispose of these computers and other hardware.  Along with considering the security of your money if you buy cryptocurrency (there have been some collapses of cryptocurrency companies recently), consider the environmental impact of cryptocurrency before you decide if cryptocurrency is right for you.