The difference between Cambridge (CCAF) and Bitcoin Mining Council (BMC) data on sustainable energy use of the Bitcoin Network is primarily due to CCAF underreporting, not BMC over-reporting of sustainable energy use, as many in the media have assumed.
Evidence:
Cambridge (CCAF) to their credit acknowledge openly that their sample represents less than half the total data-set and does not include flare-gas and off-grid mining that could "reasonably be expected to reduce emissions".
"Sample may not be sufficiently representative:
The Bitcoin mining map is based on an extrapolation of a sample of mining pool data. This sample may not be fully representative as it (i) represents less than half of Bitcoin’s total hashrate"
https://ccaf.io/cbeci/mining_map/methodology
Also
"Our estimates do not account for any activities that could reasonably be expected to reduce emissions, such as using flare-gas, off-grid (behind the meter) Bitcoin mining, waste heat recovery or carbon offsetting."
https://ccaf.io/cbeci/ghg/methodology
The conclusion when we factor in the missing data: Bitcoin runs on at least 52.6% sustainable energy.
source: http://batcoinz.com/BEEST
Are there other problems with the Cambridge data?
Yes, several shortcomings.
The mining map is now 16 months out of date (matters a lot because Kazakhstan mining is now a shadow of what it was)
Average Joules/Terahash calculation upon which their model is based is overstated. I’ve triangulated this with Mara, Luxor and Blockware who all have a very similar (and lower) calculation based on more accurate and up-to-date data about actual miner mix (more efficient than Cambridge assumptions)
There’s other issues too. But those are the main ones that lead to the host of following flow on effects
- coal incorrectly identified as major energy source
- bitcoin sustainability mix incorrectly labelled sub-50%
- bitcoin network incorrectly identified as not trending more sustainable since the China-ban
- emission intensity incorrectly overstated and labelled as increasing
- emissions per annum figure (obtained by multiplying 2 overstated figures: % fossil fuel x energy consumption ) is overstated by a factor of 2x