The BBC once again strode into a den of carnivorous Bitcoiners by publishing a piece about mining entitled: Every Bitcoin payment ‘uses a swimming pool of water.’
This piece claims to cite a “study” published in the journal Cell Reports Sustainability. The analysis in this commentary to calculate indirect water usage relied on taking the estimates for power demand and spatial distribution of Bitcoin mining from the Cambridge Centre for Alternative Finance and assuming that the indirect water usage of Bitcoin in those countries was typical for that type of energy usage in those countries.
Conducting this analysis results in an estimate of indirect water consumption of 1,573.7 gigaliters.
To calculate the direct water usage, the piece relied on assuming that Bitcoin mining operations had water usage similar to other data centers.
The author of this commentary, Alex de Vries, was the one quoted in the BBC article as saying that every Bitcoin transaction used a swimming pool’s worth of water. This number is arrived at by taking the total estimated amount of water consumed per year by the miners securing the network and dividing that number by the number of transactions that were written to the Bitcoin blockchain that year.
Namely, 1,573,000,000,000 liters/96,700,000 transactions result in 16,729 litres per transaction, or enough to fill about a 12-foot-diameter, 5-foot-deep circular pool.
Bitcoiners were quick to take to X to express their frustration with the frame of the piece, especially infuriated that de Vries chose to rely on a ‘per transaction’ value for Bitcoin, which many believe fails to capture the nature of the system.
Critics hit back at BBC Bitcoin mining piece
The critiques of this type of analysis generally will at least touch on the use of ‘per transaction’ values for either energy usage or water consumption, focusing on the fact that transacting on Bitcoin does not actually drive the energy consumption or the water usage.
To explain, the energy consumption of miners is driven by their potential rewards; they are incentivized to spend nearly as much as they stand to receive, and much of this spend is in the form of energy consumption. The rewards they stand to gain are a combination of newly ‘issued’ bitcoins and the sum of transaction fees in blocks they produce. The truth is that transaction fees are a small (though growing thanks to people finding new ways to store arbitrary data on the Bitcoin blockchain) portion of those rewards, and they are primarily driven by the newly issued coins.
What this practically means is that even if Bitcoin transactions were half as common as they currently are, we would not necessarily expect the energy or water consumption of the network as a whole to decrease.
Because of this, Bitcoiners often seem to feel that it is ‘unfair’ to focus on ‘per-transaction’ numbers because the transactions are not what are driving the consumption. Many also seem to feel that it is unfair to focus on transactions on the blockchain, believing that Bitcoin’s destiny is to have many of its transactions occur off of the blockchain.
The dynamics of this effect are even present in de Vries analysis when we realize that the calculated water use per Bitcoin transaction in 2020 ends up being approximately 1/3 of the water consumption per Bitcoin transaction in 2021. This means that in 2020, instead of a 12 foot diameter pool that’s 5 feet deep you can only have a 6 foot diameter pool that’s 5 feet deep. This was driven by the denominator (Bitcoin transactions per year) reducing from 113 million transactions in 2020 to 96.7 million transactions in 2021 at the same time that the numerator (energy consumption * water use per unit energy) significantly increased due to miners moving to Kazakhstan, which had reported water intensity numbers much greater than China. One of the implications of this is that if miners in China actually did not relocate, but instead relied on VPNs or other tools to appear to exist in other locations then that would result in an overestimate of water consumption.
For much of 2021, Cambridge University’s estimate that this report relied on reported China’s share of global mining as 0% (though with methodological notes present discussing the limitations), however, other reports suggested that China was still a significant portion of mining and relied on VPNs to hide this activity.
Cambridge itself realized this by 2022, a year not included in this water usage analysis, publishing a new analysis that discussed how they had detected a ‘re-emergence’ of Chinese Bitcoin mining activity, passing up the previously discussed Kazakhstan.
What this demonstrates is that our final calculated number both for energy consumption and water consumption ends up quite sensitive to assumptions that we have reason to think are not precise, but the true disagreement is deeper.
The fundamental disagreement
The critics and the Bitcoiners fundamentally disagree on how Bitcoin should be assessed.
The critics (at least the ones who understand what they are criticizing) do not believe that the transactions are driving the energy or water consumption of the network; what they are trying to express is something closer to (environmental costs of the system)/(use of the system) to try to understand whether the benefits of the system outweigh the costs. They believe that transactions occurring on the Bitcoin blockchain are a reasonable proxy for (use of the system).
First, Bitcoiners will argue the costs are different than they appear, pointing towards Bitcoin mining taking advantage of surplus or difficult-to-capture energy.
Furthermore, Bitcoiners think the use of Bitcoin cannot be measured by transactions, or at least not on-chain transactions. They will often point towards transactions that do not occur on-chain, on a spectrum of censorship resistance from Lightning to transfers between Coinbase accounts, all occurring without 1:1 corresponding on-chain transactions. Surely, they argue those most count as ‘use’ of Bitcoin, and therefore excluding that use is not appropriately expressing the ratio of (environmental costs of the system)/(use of the system).
Additionally, Bitcoiners will argue that the value of Bitcoin itself is in part related to factors that (they believe) are intrinsically linked to features tied to these costs. For example, if you believe that Bitcoin’s value is tied to censorship resistance and that this censorship resistance is tied to the specific incentives of Bitcoin mining as it exists today, then it is possible to argue that things that depend on the ‘value’ of Bitcoin are used benefitting from that cost.
So, if Bitcoin is valuable and you can use that value to achieve other economic value, then that should be considered a use as well. If Bitcoin is being used as collateral for lending and the funds that are borrowed are used for other economically important activities, then perhaps that is the use of Bitcoin. Or perhaps the value of Bitcoin is instead being used as a reserve for economically important actors; then perhaps that is use as well.
Remember, Bitcoiners HODL, and HODLing is not transacting.
It is possible then that good-faith actors on both sides are honestly trying to assess (environmental costs of the system)/(use of the system) but are just disagreeing on what the use of the system looks like. For spherical cryptocurrencies in an intellectual vacuum, we can see that Bitcoiners have a theoretical point, and we can objectively observe that there is non-zero use of Bitcoin that occurs without corresponding transactions.
The critics, however, would respond that Lightning adoption has been extraordinarily slow, Bitcoin transactions for merchants using things like Coinbase Commerce have been slow to see adoption, and Bitcoin collateralized lending has already caused significant harm in multiple cases. They may also suggest that Bitcoiners are wrong that censorship-resistance or decentralization or whatever is not actually tied to the costs in the manner that they believe. This is why some critics will propose ideas that are culturally unacceptable to Bitcoiners, like hard-forking to a new chain relying on proof-of-stake.
The fundamental question that you would assume most participants in this debate are trying to answer is: Are the costs of this system outweighed by the benefits? Once you stop getting distracted by ratios, this is the natural endpoint, and for most of the critics, when they look at Bitcoin, they cannot see enough value provided by the system to justify these costs. Bitcoiners believe very deeply in the value of the system, so deeply that changing consensus like other chains have is completely untenable, and as such, the costs must be justified.
Update December 4, 21:18 UTC: The article discussed in this piece was peer-reviewed. A previous version of this article suggested otherwise.