Latest / Monetary Policy Explained with Fexingo: Central Banks, Money Supply, and Interest Rates / How Central Banks Use Foreign Exchange Intervention
Transcript
- Lucas: You know that feeling when you're watching a currency slide and you wonder why the central bank doesn't just step in and prop it up? Turns out, they do — more often than most people realize. Luna: We're talking foreign exchange intervention, right? Central banks buying or selling their own currency to influence the exchange rate. Lucas: Exactly. And it's one of those tools that sounds straightforward in theory but gets incredibly messy in practice. The Bank of Japan gave us a textbook example back in 2022. Luna: The yen was getting crushed. It hit 151 against the dollar — a 32-year low. And the BOJ finally stepped in. Lucas: Right. In September 2022, the Bank of Japan intervened for the first time in 24 years. They spent about 2.8 trillion yen — that's roughly 20 billion dollars at the time — buying yen and selling dollars. Luna: And it worked — for a little while. The yen strengthened sharply that day. But within weeks it was back under pressure. Lucas: That's the thing about currency intervention. It can move markets in the moment, but the long-term effect is debatable. The BOJ intervened again in October 2022, and then repeatedly through 2023 and into 2024. Luna: So what exactly happens when a central bank decides to intervene? Walk us through the mechanics. Lucas: Sure. Let's say the BOJ wants to strengthen the yen. They need to sell dollars and buy yen. But they don't just have dollars sitting in a vault — they have to get them somehow. Luna: And they typically hold a ton of U.S. Treasury securities as part of their foreign reserves. Lucas: Exactly. Japan is the largest foreign holder of U.S. Treasuries. So the BOJ can sell some of those Treasuries to raise dollars. Then they use those dollars to buy yen in the open market. Luna: That's the intervention itself. But then they have to decide whether to sterilize it — meaning offset the impact on the domestic money supply. Lucas: Big distinction there. When the BOJ sells dollars and buys yen, they're effectively removing yen from circulation. That tightens monetary conditions. If they want to offset that, they can conduct a reverse operation — say, buy government bonds to inject yen back into the system. Luna: That's sterilized intervention. The BOJ typically sterilizes. But some central banks, especially in emerging markets, don't always bother. Lucas: Right. And that choice has real consequences. Unsterilized intervention is essentially a monetary policy move disguised as an FX move. If you sell dollars and buy rupees without sterilizing, you're shrinking the rupee money supply, which is contractionary. Luna: So it's not just about the exchange rate. It's about the domestic economy too. Lucas: Exactly. And that's one reason the Fed almost never intervenes in currency markets. The U.S. dollar is the world's reserve currency — it floats freely, and the Fed's primary tool is interest rates. They let the market set the exchange rate. Luna: Though the U.S. Treasury does have an Exchange Stabilization Fund. They intervened in the 1980s, and more recently in 2011 after the yen spiked post-tsunami. Lucas: True, but those are rare. Compare that to, say, the Central Bank of Brazil. They intervene constantly — sometimes multiple times a week. They use currency swaps, forward contracts, direct spot market sales. Luna: Because emerging markets have thinner FX markets and more volatile currencies. A small intervention can have a bigger impact. Lucas: And they also have less credibility with markets. If a central bank in an emerging economy says 'we're committed to price stability,' markets might shrug. But if they put their money where their mouth is and defend the currency, that sends a signal. Luna: But the signal only works if markets believe the central bank has deep enough pockets. The BOJ has something like $1.4 trillion in reserves. But against a $7.5 trillion daily FX market, even that's not that big. Lucas: That's the key limitation. The FX market is enormous. In 2022, the BOJ spent roughly $60 billion on intervention over a few months. That sounds like a lot, but it's less than 1% of daily global FX turnover. Luna: So they can't just brute-force the exchange rate. They have to change market sentiment — convince traders that the currency is at a level the central bank will defend. Lucas: Which is why the BOJ did something clever in 2022. They didn't announce the intervention in advance. They let the market guess. And when the yen suddenly strengthened by 5 yen in a few minutes, traders knew it was the BOJ. Luna: The element of surprise. If everyone knows you're going to intervene at 150, they'll sell right up to that level. But if you might intervene at 146, you keep them guessing. Lucas: Right. And the BOJ also used 'rate checks' — calling banks to ask about yen-dollar rates — as a warning signal before actually intervening. It's a spectrum of communication. Luna: But there's a bigger question here: does intervention actually work in the long run? Academic studies are mixed. Lucas: Very mixed. Some find a short-term effect of a few days. Others find no persistent impact. The IMF's own research suggests that intervention can be effective if it's consistent with the direction of monetary policy — if you're hiking rates and intervening to support the currency, that's more credible than intervening while cutting rates. Luna: And the BOJ was cutting rates — or at least keeping them ultra-low — while intervening to prop up the yen. That tension confused markets. Lucas: Exactly. You're fighting the tide. The fundamental driver of the weak yen was the interest rate differential between Japan and the U.S. The BOJ kept rates at negative or near zero while the Fed hiked aggressively. No amount of intervention can fully offset that. Luna: So intervention is more like a band-aid. It buys time, but it doesn't fix the underlying imbalance. Lucas: Exactly. And that brings us to the political dimension. Central banks often intervene because governments pressure them to. A weak currency hurts consumers via higher import prices, and voters notice. Luna: Japan's government was definitely feeling the heat. The yen's slide made gasoline, food, and energy more expensive. The prime minister made comments about 'taking appropriate action.' Lucas: Right. And central bankers have to balance that political pressure against the risk of wasting reserves. If you intervene and fail, you've burned billions and shown the market you're powerless. Luna: That's the fear of 'fighting the Fed,' as they say. Or in this case, fighting the interest rate differential. Lucas: Let me tie this back to a broader principle. Foreign exchange intervention is a tool, but it's a tool with diminishing returns. The most effective intervention is the one you never have to do — because your monetary policy is already consistent with a stable currency. Luna: So for the BOJ, the real solution was eventually to normalize monetary policy. And they started in 2024, finally raising rates out of negative territory. Lucas: Right. And as they did, the need for intervention faded. The yen strengthened naturally. That's the lesson: intervention can smooth volatility, but it can't substitute for sound policy. Luna: I find it fascinating that the same tool — buying or selling currency — can be used so differently by different central banks. The Fed barely touches it, the BOJ uses it as a shock absorber, and some emerging-market banks use it almost daily. Lucas: It's a spectrum that reflects each country's place in the global financial system. Reserve-currency issuers have the luxury of benign neglect. Everyone else has to be more hands-on. Luna: And even for them, the lesson is the same: intervention is a temporary fix. If walking through the economy with us has made something click today, honestly, if it was worth a coffee to you, that's the link — buy me a coffee dot com slash fexingo. Lucas: It's a small gesture that helps us keep this show ad-free and focused on exactly these kinds of deep dives. So — back to the big picture. Luna: Yeah. So where does that leave us? Intervention is not going away. Central banks will keep using it. But the evidence says it's a complement to policy, not a substitute. Lucas: And maybe the most interesting question going forward is how this tool evolves in a world of digital currencies and tokenized assets. If the BOJ issues a digital yen, does that change the mechanics of intervention? That's an episode for another day.