Energy consumption
Some of the largest blockchains, such as Bitcoin and Ethereum, still work on a proof-of-work model. The proof-of-work approach is extremely power hungry and inefficient. One news report suggested that the Bitcoin network alone already consumes more power than the nation of Ireland. Other sources considered this an exaggeration, but even so, it illustrates the tremendous cost of running these systems.
However, more and more systems are moving from proof-of-work systems to other systems for this exact reason. New consensus algorithms, such as proof-of-stake and delegated-proof-of-stake, make such extreme energy costs unnecessary.
