Latest / Monetary Policy Explained with Fexingo: Central Banks, Money Supply, and Interest Rates / How Central Banks Use Currency Intervention
Transcript
- Lucas: So last week, the Bank of Japan confirmed it had spent roughly 5.5 trillion yen — that's about $37 billion — in a single day back in late April to prop up the yen. And the market barely blinked. The yen weakened again within hours. That's the kind of moment that makes you ask: does currency intervention even work? Luna: It's a huge number for one day. But I remember the old playbook — the Bank of Japan and the Swiss National Bank used to move markets for weeks with smaller sums. What changed? Lucas: The short answer is that interest rate differentials are so vast that intervention is fighting a tsunami with a garden hose. Let's back up. Currency intervention is when a central bank buys or sells its own currency to influence the exchange rate. If the yen is too weak, the BOJ sells dollars from its reserves and buys yen. That pushes the yen up. Simple in theory. Luna: But in practice, they did exactly that — and the yen kept falling. Lucas: Right. Because the underlying driver was the gap between U.S. interest rates, which were above 5 percent, and Japan's near-zero rates. That gap makes it profitable for investors to borrow yen, sell it, and buy dollars to put in U.S. bonds. That's the yen carry trade. Every time the BOJ bought yen, a thousand hedge funds sold it right back. Luna: So intervention only works if it changes expectations, not just the spot rate. Lucas: Exactly. And there are two kinds: sterilized and unsterilized intervention. Unsterilized intervention is when the central bank buys its currency and does not offset the impact on the domestic money supply. So if the BOJ sells dollars and buys yen, yen leave the banking system, raising short-term interest rates. That can make the currency more attractive. But it means the central bank is effectively tightening monetary policy, which may conflict with its domestic goals. Luna: And sterilized is when they neutralize that? How? Lucas: They buy yen by selling dollars, but then they buy government bonds to inject the yen back into the banking system. So the money supply stays unchanged. The exchange rate moves purely through the supply-demand mechanics of the forex market, without affecting interest rates. That's what the BOJ has been doing. And it's widely considered less effective, because the interest rate incentive to short the yen remains. Luna: So the BOJ was basically running on a treadmill. They sold dollars, bought yen, then re-lent the yen back into the system. The carry trade stayed profitable. Lucas: Exactly. And the scale is staggering. In the quarter ending June, the BOJ likely spent over $60 billion. That's roughly 7 percent of Japan's total foreign reserves. For a country that relies on those reserves for crisis management, that's not trivial. And the effect? The yen is still weaker than it was before the intervention started. Luna: So when does intervention actually work? I'm thinking of the Plaza Accord in 1985, or the SNB's cap on the franc in 2011. Lucas: Good examples. The Plaza Accord worked because it was coordinated among five major central banks and backed by real policy changes. The SNB's franc cap worked because they set a hard floor and promised to buy unlimited foreign currency to defend it — and they did. That's commitment. The BOJ's recent moves look more like a one-off slap on the wrist. Luna: But there's a political angle too. Japan's finance ministry is under pressure from exporters and lawmakers. They have to be seen doing something. Lucas: Absolutely. A lot of currency intervention is signaling. You're telling markets: 'We are watching, and we will step in if the move becomes disorderly.' The hope is that speculators get cautious. But if the fundamentals are clear — wide rate gap, weak growth, large trade deficit — the signal loses its power. Luna: What about other central banks right now? The Swiss National Bank has been intervening to weaken the franc, because it's too strong for their export sector. Lucas: That's the flip side. The SNB wants a weaker franc. They buy foreign currency and sell francs. And they've been doing it for years. But because they operate in a very different environment — Switzerland has a current account surplus and low inflation — they have more room. They can afford to accumulate reserves. Luna: And they've also used negative interest rates to discourage franc inflows. That's another tool. Lucas: Right. Intervention is most effective when it's backed by other policy levers. If you're only trading in the spot market, you're just one more participant. And your balance sheet is finite. The market's daily turnover in USDJPY is over $500 billion. A central bank spending $37 billion in a day can move the rate momentarily, but it can't change the tide. Luna: So the lesson is that intervention can smooth volatility, but it can't set the level. Lucas: That's the consensus among academic economists. A 2019 study by the Bank for International Settlements looked at decades of intervention data. They found that sterilized intervention typically moves the exchange rate by only 1 to 2 percent in the short run, and the effect fades within weeks. To have a lasting impact, you need to change the interest rate differential or the risk premium. Luna: Which is why the BOJ's eventual policy shift matters more than any intervention. If they raise rates, that'll do more than any dollar sale. Lucas: Exactly. And we've already seen hints. In March, the BOJ ended negative rates. If they follow through with more hikes, the carry trade becomes less attractive, and the yen might find a floor naturally. Intervention can buy time, but it's not a substitute for policy. Luna: There's also a risk of losing credibility. If you intervene and the market brushes it off, you look weak. Lucas: That's the big concern. The BOJ has stepped in repeatedly over the past two years. Each time, the effect has been smaller. Some traders now see intervention as a buying opportunity: they sell yen into the BOJ's buying. That's a dangerous dynamic. It's like the central bank is feeding the very speculation it's trying to curb. Luna: So what's the takeaway for our listeners? When they read 'central bank intervenes in currency markets,' they should ask: sterilized or unsterilized? Coordinated or solo? And what's the interest rate backdrop? Lucas: That's exactly the framework. And one more thing: look at the reserves. If a central bank is burning through 10 percent of its reserves in a quarter, that's unsustainable. Eventually, they have to let the currency adjust. Luna: It's a reminder that central banks aren't all-powerful. They have tools, but each tool has limits. Lucas: Speaking of limits — one thing we're proud of on this show is that we don't run ads. We keep the focus on the economics. If you've found this walk through the central bank toolkit useful, there's a way to support that approach. It's buy me a coffee dot com slash fexingo. No pressure, really. Just a way to keep the show ad-free and independent. Luna: Yeah, it's a small gesture that goes a long way. We appreciate everyone who chips in. Lucas: Alright. So to wrap up — currency intervention is like a fire extinguisher. It works great for small flare-ups. But if the whole room is on fire, you need to address the cause, not just spray at the flames. For Japan, that cause is the interest rate gap. Until that narrows, the yen's weakness story isn't over. Luna: And for central banks watching from the sidelines, the lesson is: use intervention sparingly, and only when you have policy backing it up. Otherwise, you're just throwing money into the wind. Lucas: Well said. That's it for this episode. We'll be back next time with another tool from the central bank's playbook.