Recent weeks have witnessed a surge in borrowing costs globally, propelled by volatile government bond markets. This marks a significant challenge for the global economy, raising concerns about debt sustainability in advanced nations.
Since July, US Treasury yields have trended upward, with yields across maturities from 2-year to 30-year notes generally increasing. On September 10th, the US 10-year Treasury yield approached 4.95%, its highest level since January 2025, while the 30-year yield climbed to 5.37%, a peak not seen in two decades.
Other highly indebted economies have also seen their bond yields hit new highs. The UK's 30-year yield reached its highest point since 1998, while Japan's 10-year yield touched 3% for the first time since 1996. Similarly, yields in Germany and France have risen to levels not observed in over ten years.
Fan Yanhui, a professor at the China School of Finance at the University of International Business and Economics, explains that bond prices and yields move inversely. When markets anticipate interest rate hikes, investors sell off government bonds, causing prices to fall and yields to rise. The current downtrend in developed market bond markets is directly tied to expectations of central bank tightening, with markets already pricing in clear rate hikes from the Federal Reserve and the Bank of Japan. Many advanced economies have already begun raising rates, and financial markets are reacting accordingly.
The Bank of New Zealand announced a rate hike on September 2nd, marking its second such move this year. The Bank of Japan raised rates in June, and the Bank of Korea followed with consecutive hikes in July and August. Meanwhile, the European Central Bank recently increased its benchmark interest rate to 2.5% during a renewed bond market sell-off. The ECB has also warned that inflation in the eurozone is expected to remain well above its 2% target for a "considerable period" due to persistently high energy prices stemming from the Middle East conflict.
Why are advanced economies resorting to rate hikes now? Fan points to high international oil prices caused by the US-Iran conflict as a key external factor. Japan's heavy reliance on oil imports makes it particularly vulnerable to imported inflation, while many European nations are also facing inflationary pressures from rising energy costs. Central banks are adopting tighter monetary policies in an attempt to control inflation.
A recent report from OPEC indicates that Saudi Arabia's crude oil production averaged 6.2 million barrels per day in August, its lowest monthly figure since 2026 and a decline of 23% from July. S&P Global Energy suggests that with the prospect of a full resolution to the US-Iran conflict fading, oil markets are entering a "new normal" of high prices. This is the first time the research firm has forecast that Middle East crude output will not return to pre-conflict levels by the end of 2027.
The Middle East turmoil has driven up prices for oil and natural gas, with European gas prices already more than double their pre-conflict levels and likely to rise further as countries replenish storage ahead of winter. Policymakers are responding to increasing signs of upward price pressure. Average annual inflation in advanced economies has stalled, no longer falling toward the 2% target adopted by most nations, and has actually ticked slightly higher in recent months. In August, the eurozone's annual inflation rate reached 3.3%, a three-year high.
Aside from energy, other factors are at play. Estimated average annual "core" inflation in advanced economies, excluding energy and food prices, has risen from 2.7% in early 2026 to 2.9% currently. Simultaneously, advanced economies generally face significant debt burdens, such as the US federal debt surpassing $40 trillion and high levels of public debt relative to GDP in Japan. The combination of high debt and high inflation intensifies concerns about debt sustainability, contributing to the broad decline in bond markets.
The interplay of these factors makes it clear that the market is reflecting worries about fiscal sustainability. Under significant debt loads, higher interest rates mean increased government borrowing costs. If a country's bond yields approach or exceed its economic growth rate, it signals market apprehension about that nation's ability to manage its debt. Currently, US Treasury yields for one-year and longer maturities are above 4%; if they consistently exceed GDP growth, this could trigger volatility in US debt markets and international financial markets.
However, historical patterns suggest that in times of international financial turmoil, global capital often flows back to the US as a safe haven, purchasing Treasury bonds and pushing their prices up while yields fall. This dynamic can offer some relief to the US. Given the dollar's status as the world's reserve currency and the importance of the US economy, fluctuations in the US bond market have a spillover effect internationally.
Looking ahead, the direction of bond markets will largely depend on the persistence of the US-Iran conflict and its impact on oil prices and inflation expectations. Given the current situation in the Middle East, a quick end to the conflict seems unlikely. If a balanced state of "stalemate without escalation" holds, market expectations of heightened conflict may weaken, potentially easing inflation expectations and upward pressure on interest rates in advanced economies, which would help stabilize bond markets. Nevertheless, for advanced economies, navigating the impact of high oil prices on supply chains and addressing massive debt levels remains an ongoing and significant test.