Seeing as how many are overzealous in their climate change crusade. Enough so to negatively stigmatize PoW and the crypto mining industry. Perhaps they can be appeased by a stronger effort towards a carbon neutral society.
If your source is correct and that 25% of global warming is caused by methane (these estimations are often wrong to begin with so I take the estimation at face value), then whatever emissions produced from landfills are merely noise in system and of little importance. Humans have to produce pollution, it's a product of existing. The climate change alarmist suggest that crypto mining doesn't produce anything tangible and subsequently becomes an easy target opposed to something like landfills, a necessity. I don't suppose even the most radical climate change activist would support eliminating landfills allowing waste to pile up in local environments.
I don't take these people very seriously, anyways. We would be much better off not trying to aim for a carbon free society and use energy sources until depletion. Then switch to nuclear energy. Carbon based fuel will last at least 5 more decades.