They say Bitcoin is a waste of electricity
As long as mining is profitable, the difficulty will increase. As long as difficulty increases there will be more mining. This means that periodically, mining will damage the environment increasingly.
Not necessarily. Use of renewables is considerable, and is growing. The 'waste of electricity' argument will become less relevant over time.
A
Cambridge University study last year into use of renewables in crypto mining found that 'the majority of identified mining facilities use
some share of renewable energy sources as part of their energy mix', and that the average contribution of renewables is around 28%.
From page 84 of the report (my bold):
Less than a quarter of identified miners do not use any forms of renewable energy sources at all, although the energy mix of one quarter of facilities could not be identified. Certain regions such as Xinjiang Province in China rely almost entirely on coal. Nevertheless, weighing the farms by identified megawatts results in a similar picture and shows that cryptoasset mining is much less dependent on fossil fuels than anticipated. Identified facilities draw on average 28% of their energy requirements from renewables. However, the share of renewables varies considerably from one facility to another: while some only use a marginal proportion, others run almost exclusively on renewables. On average, roughly 28% of the total energy supply for both small and large facilities is generated through renewable sources. Among renewables, hydroelectric power is the most frequently used energy source. Nearly half of the identified megawatt capacity featured in the cryptoasset mining map is generated through hydropower. It is worth noting that the mining map identifies 30% of the lower-bound total energy consumption estimate. An interesting pattern emerges when comparing the energy mix with the location of the respective mining facilities. Regions with substantial green power sources seem to become attractive targets for miners, since these locations tend to overlap with places where there is an abundance of low-cost hydroelectric power that is unused and stranded. Energy in these locations is often cheap because demand cannot compensate the oversupply.