Blockchain technology and its popular cryptocurrencies such as bitcoin and Ethereum have most revolutionary technological advances in recent history, capable of transforming businesses, government, and social interactions. However, there is a darker side to this technology which is the immense energy consumption and potential climate impact of the blockchain and cryptocurrencies. According to Digiconomist's Bitcoin Energy Consumption Index, Bitcoin has such an impact on the environment (118.9TWh/year) – considering the huge amount of energy used – that it compares to the power consumption of countries like the Netherlands (117.1 TWh/year) or Pakistan (125.9TWh/year). There is an urgent need to address this danger to ensure the long-term sustainability of IoT.