Critiquing the Carney critique of central bank digital currency

Over on the message board we've been discussing the implications of central bank-issued digital currency, otherwise known as CBDC. One view is that a central bank digital currency would lead to increased financial instability, Bank of England governor Mark Carney being a vocal proponent of this idea. There are a lot of criticisms that can be leveled against central bank digital currency, but the Carney critique is the one that worries me the least. Let's see why. 

First off, let's establish what we mean by digital currency. Imagine that a central bank has discovered a technology that allows it to create an exact digital replica of the banknote. Like banknotes, these digital tokens are anonymous and untraceable. To make use of them, people don't have to register for an account. Rather, the tokens are held independently on one's device, sort of like how paper money is held in one's wallet without requiring any sort of registration with the issuing central bank. This combination of features makes it impossible for the central bank to censor or prevent people from using digital currency, in the same way that the central bank can't stop people from trading paper money among themselves.

Unlike banknotes, which can only be passed face-to-face, digital currency can be transferred instantaneously over the internet. There are no storage and handling costs. $10 million dollars worth of $20 bills takes up a lot of space and is awkward to carry around, but in the digital world that same nominal amount has neither volume nor weight. Lastly, digital currency is cheap to create, requiring only a few keyboard strokes. Cash requires large printing machines, ink, and paper.

Having established what a digital currency is, let's introduce it into the economy. The central bank announces a demonetization of all banknotes and coins, offering $1 of digital currency for each $1 worth of cash. Anyone who want to withdraw money from their bank account will now get digital currency, not banknotes. No one visits ATMs or the bank teller anymore to make a deposit or withdrawal: with an internet-connected device, deposits and withdrawals can be made from bed, the toilet, or while commuting on the bus.

Carney's contention is that the introduction of a digital currency could hurt the banking system:
"...a general purpose CBDC could mean a much greater role for central banks in the financial system. Central banks may find themselves disintermediating commercial banks in normal times and running the risk of destabilising flights to quality in times of stress."
First, let's deal with Carney's normal times critique. The idea here is that by introducing a digital version of the banknote, a significant proportion of existing depositorsthose with chequing and savings accountswill desert their bank because they want to hold sleek and shiny central bank digital currency instead. (Presumably they didn't desert their banks when banknotes were around because cash was bulky and couldn't be transferred instantaneously over a communications network.) By causing a mass draining of depositsi.e. disintermediating commercial banksa new digital currency would impair the ability of banks to make loans, and this would affect the economy in a negative way. 

To show why I don't think the Carney critique holds, we need to investigate one of the important differences between cash/digital currency and bank deposits. When people open bank accounts, what interests them is not just the idea of making payments with those accounts but also maintaining a relationship with the bank in order to benefit from a smorgasbord of other financial services. People with bank accounts are like subscribers to a magazine, they want an ongoing connection.

Those who use cash, on the other hand, would rather just buy the magazine once rather than subscribe to it, orfor another analogyprefer using disposable plastic plates to maintaining a set of their own plates. Cash is a one-time use commodity; once you spend it, any relationship to its issuer is severed. This lack of an ongoing connection provides value to some people. Consider the process of budgeting. By sticking some cash in an envelope dedicated to groceries, another for rent, presents, entertainment, clothing, you can closely monitor your spending over the course of a month. Once the cash is used up, spending stops. With a bank, however, a connection remains even after someone's balance has fallen to zero, spending potentially continuing via overdrafts and credit cards. People who may not trust themselves to stay within their means may therefore prefer the one-time use nature of cash.

So when digital currency replaces cash, I don't anticipate a mass migration from bank accounts to digital currency. Depositors who have already chosen a subscription-based banking solution over a one-time payments solution won't change their minds when the next generation one-time use product is introduced. Which isn't to say that there won't be some sort of migration out of bank deposits and into a new digital currency. Consider upstanding members of society who have always wanted to make anonymous digital payments but haven't had the chance to do so because the only anonymous option theretofore available to themcashwas a physical medium, and so instead they have opted for the inferior option of non-anonymous digital payments services of a bank. This group of anonymity seekers will make the switch. 

But the migration of legitimate anonymity seekers out of bank deposits into digital currency will be counterbalanced by a reverse migration out of cash into bank deposits. Let's think for a moment about who uses cash. Illicit users like criminals and tax evaders are big users, and when cash is demonetized they will all shift into digital currency in order to preserve their anonymity. Likewise, licit users of cash who want to keep using a one-time use payments option will opt for digital currency. The undocumented and those who are too poor to qualify bank accounts will also make the migration into censorship resistant digital cash.

That leaves one major group of cash users unaccounted for: those who use cash not because they like any specific feature that it provides but out of pure force of habit. With cash being cancelled, habitual users will have no choice but to switch into some other payments option. And since deposits are the time-tested option, it is likely that many will move their funds into the banking sector. If this wave of inbound habitual users is greater than the wave of outbound anonymity seekers, then the introduction of a digital currency may actually be lead to an increase in bank intermediation rather than Carney's disintermediation!


So if a digital currency won't affect the banking system during regular times, what about Carney's times of stress criticism? The general criticism here is that during a crisis, households and businesses will desperately shift their deposits into the ultimate risk-free asset: central bank money. Presumably when deposits were only redeemable in banknotes (as is currently the case) and one had to trudge to an ATM to get them, this afforded people time for sober contemplation, thus rendering runs less damaging. But if small depositors can withdraw money from their accounts while in their pajamas, this makes banks more susceptible to sudden shifts in sentiment, goes the Carney critique.     

I don't buy it. Small depositors won't exit banks during a crisis because their money is insured up to $250,000 (in the US). But even in jurisdictions without deposit insurance, I still don't think that shifts into digital currency in times of stress would exceed shifts into banknotes. A bank will quickly run out of banknotes during a panic as it meets client redemption requests, and will have to make arrangements with the central bank to get more cash. Thanks to the logistics of shipping cash, refilling the ATMs and tellers will take time. In the meantime a highly visible lineup will grow in front of the bank, exacerbating the original panic. Now imagine a world with digital currency. In the event of a panic, customer redemption requests will be instantaneously granted by the bank facing the run. But that same speed also works in favor of the bank, since a request to the central bank for a top-up of digital currency could be filled in just a few seconds. Since all depositors gets what they want when they want, no lineups are created. And so the viral nature of the panic is reduced.

But what about large depositors like corporations and the rich who maintain deposits well in excess of deposit insurance ceilings? During a crisis, won't these sophisticated actors be more likely to pull uninsured funds from a bank, which have a small possibility of failure, and put them into risk-free central bank digital currency?

I disagree. In a traditional economy where banknotes circulate, CFOs and the rich don't generally flee into paper money during a crisis, but into short-term t-bills. Paper money and t-bills are government-issued and thus have the same risk profile, t-bills having the advantage of paying positive interest whereas banknotes are barren. The rush out of deposits into t-bills is a digital one, since it only requires a few clicks of the button to effect. Likewise, in an economy where digital currency circulates, CFOs are unlikely to convert deposits into barren digital currency during stress, but will shift into t-bills. The upshot is that banks are not more susceptible to large deposit shifts thanks to the introduction of digital currencythey always were susceptible to digital bank runs thanks to the presence of short-term government debt.

The ability to mitigate shifts out of the banking system during times of stress may be even more potent in a world with digital currency than one without. During a crisis a central bank will generally reduce its main policy interest rate in order to stimulate the economy, short-term market interest rates falling in sympathy. Now, consider an economy with banknotes. Even as short-term rates fall, the interest rate on banknotes stays constant at 0%, the effect being that the relative return on banknotes steadily improves. This only encourages further shifts out of the banking system into cash.

Digital currency updates the cash model by introducing a wonderful new invention: the ability to adjust the interest rate on cash. Now when the central bank reduces its policy rate to offset the weakening economy, it can simultaneously reduce the rate on digital currency. This has the effect of maintaining a constant relative return on currency throughout the crisis. So unlike a banknotes-only world in which the relative return on notes steadily improves as the crisis deepens, thus encouraging disintermediation of the banking sector, a digital currency-only world guards against the sort of return differential that might engender disintermediation.


So the Carney critique, which frets over mass adoption of digital currency, doesn't amount to much, in my view. A better critique of digital currency is the exact opposite: instead of mass adoption, it is very possible that no one (apart from criminals and tax evaders) uses the stuff.

Let's see why digital currency could fail on takeoff. One potential migration pattern I mentioned above involves upstanding members of society who desire anonymous online payments adopting digital currency. But what if there just aren't that many people who care about online privacy? Countries like Sweden, where banknote usage is plummeting, give credence to this concern while surveys of cash users in the eurozone show that anonymity is not terribly important to them:

Another large base of potential digital currency users includes all those who value cash for both its throw-away nature and lack of censorship. But what if these people choose to adopt pre-paid debit or credit cards instead, both of which are open systems that do not obligate users to maintain an ongoing relationship with the issuer?

If neither of these blocks of licit users adopts digital currency, that leaves only criminals and tax evaders keen to use a new central bank digital currency. For a central banker who is advocating the stuff, that's not a very firm political leg to stand on. In sum, Carney has got it all wrong. A central bank digital currency is less likely to have a massively disruptive effect than it is to arrive stillborn.

PS: Thanks to Antti, Oliver and the rest on the discussion board for helping me think about this more concretely.

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