Bond Yields Surge as Inflation, Fiscal and AI Debt Weigh on Markets

Global bond markets are undergoing one of their most severe repricings in years. The selloff picked up pace on Tuesday, September 1, and continued into Wednesday, with investors grappling with fresh inflation threats, rising oil prices, worsening fiscal conditions and the prospect that central banks may maintain tighter policy for an extended period.

The magnitude of the move stands out. The US 10-year Treasury yield rose to roughly 4.81%, near a three-year peak, and a climb towards 5% is increasingly seen as plausible. Japan's 10-year government bond yield topped 3%, the highest in three decades, and Australia's 10-year yield hit 5.198%, a level not seen in over 15 years. In Europe, German Bund futures sank to their lowest since 2011, while French OAT futures also set new record lows. The UK's 30-year gilt yield, meanwhile, reached levels last observed in 1998.

Investors who have favoured equities in recent years may find bonds increasingly appealing as yields rise, and bonds' diversification benefit could grow if stock market momentum eventually fades.

Oil has reignited the inflation problem

The direct trigger for the latest selloff was a fresh spike in energy prices, as hostilities between the US and Iran resumed near the Strait of Hormuz.

WTI crude jumped over 5%, topping $90 a barrel, and Brent gained more than 4% to surpass $94. The latest disruption follows a decline below $70 earlier this summer, making the turnaround especially swift.

For those holding bonds, the issue goes beyond higher oil costs. Energy prices can flow into transport, manufacturing, food and household expenses, possibly generating a second inflation wave. That is significant because the market had been hoping inflation would moderate enough for central banks to hold rates steady or cut them.

This geopolitical shock undermines that expectation.

Eurozone inflation, for instance, picked up to 3.3% in August according to early figures, with energy inflation notably high. Simultaneously, Brent crude has drifted back towards $96 a barrel.

This makes for a challenging backdrop for government debt. Anyone buying a 10-year bond today requires compensation for the time value of money and for the risk that inflation will diminish the real value of future coupons. Rising inflation expectations typically prompt investors to seek higher yields.

The outcome is a self-reinforcing loop: energy price hikes lift inflation expectations, driving yields up and raising borrowing costs throughout the economy.

Fiscal concerns are becoming impossible for bond markets to ignore

The oil shock is just the most recent catalyst. Beneath the selloff lies a deeper structural issue: governments are loaded with historically high debt loads while borrowing costs have moved far from zero.

The US national debt neared $40 trillion in July, increasing by over $3 trillion in the prior year. Across advanced economies, investors are growing more sceptical about how governments will fund ongoing deficits without substantially stronger growth, expenditure reductions or tax increases.

Japan stands out as a crucial case. Its 10-year yield has climbed to levels not observed since the 1990s, as investors reconsider inflation and the nation's fiscal trajectory. Higher debt-service costs could limit the government's capacity for additional fiscal stimulus.

The same pattern appears in Europe and the UK. The UK's public-sector net debt hit nearly 95% of GDP by June 2026, and servicing costs are still historically high. France, too, is under growing scrutiny due to its ongoing budget shortfall and political instability.

This generates what is sometimes termed a fiscal risk premium. If governments must issue ever-larger amounts of debt, investors might require higher yields to take on that supply.

Higher yields also make refinancing costlier, possibly necessitating further borrowing. That is the debt dynamic troubling bond investors more and more.

Central banks may not be able to rescue the bond market

During most of the post-financial-crisis era, investors counted on central banks to prop up government bond markets when economic conditions worsened.

That assumption now stands on much shakier ground.

The current inflation jolt is especially awkward, arriving as central banks are already doubting that inflation is fully tamed. Recent remarks from Federal Reserve Chair Kevin Warsh have reignited expectations of a rate hike in September, and markets are also pricing in higher odds of further tightening in other regions.

The US 2-year Treasury yield, highly responsive to monetary policy expectations, rose to roughly 4.41% on Wednesday, its strongest reading since January 2025. According to Reuters, markets were assigning about a 68% chance of a US rate increase later in September.

This matters for the longer-dated part of the bond market. If investors think central banks will maintain elevated rates for an extended period, the case for buying long-duration government bonds at prior yields weakens.

So the market is not simply waiting for central banks to declare rate increases. Bond investors are already tightening conditions on their own.

The AI boom is creating an unusual bond supply problem

Another element setting the current climate apart is the massive corporate debt issuance tied to artificial intelligence.

The biggest tech firms are pouring hundreds of billions into data centres, chips and computing infrastructure. More of this spending is being funded via debt rather than solely from internal cash flow.

According to Reuters data, the five leading AI hyperscalers—Alphabet, Amazon, Meta, Microsoft and Oracle—had issued roughly $220 billion of debt by August 2026.

The Bank of England has pointed out the magnitude of this trend: investment-grade debt from hyperscalers in the first six months of 2026 was roughly equivalent to UK gilt issuance in that same half.

This is significant because investors have limited capital. A flood of highly-rated corporate bonds with appealing yields can vie directly with sovereign debt. The upshot is an additional force pushing yields higher, especially at the longer end of the curve.

Why higher yields could make bonds attractive now

At this juncture, the current selloff presents an interesting chance for investors.

For years, near-zero rates rendered bonds relatively unappealing. Investors gleaned scant income from government debt, pushing capital into equities, corporate credit, real estate and other risk assets.

That setting helped fuel the equity rally of recent years. Robust earnings growth, especially from technology and AI firms, also enabled stocks to keep outpacing even as valuations grew costly.

But the investment calculus may be shifting.

A US 10-year Treasury yield near 4.8% offers investors a considerably higher initial income than they could get in the zero-rate era. Should yields eventually fall—due to moderating inflation or slowing growth—holders of longer-duration bonds could also enjoy capital gains.

This yields a potentially appealing dual return structure: current income and possible price appreciation down the road.

The contrast with equities is becoming more pertinent. Stocks can still beat bonds if earnings growth stays strong, but higher bond yields increase the discount rate on future corporate profits. All else being equal, that diminishes the appeal of pricey growth stocks.

Higher yields also raise financing costs for leveraged firms and squeeze heavily indebted businesses. Hedge funds and other leveraged players active across various asset classes can become more exposed as funding costs and volatility climb.

This does not imply that investors should ditch equities. Sustained corporate earnings, AI-driven productivity gains and resilient economic growth can still underpin stocks. Yet it undermines the notion that a portfolio should be heavily weighted in equities just because stocks performed remarkably well in the past few years.

For diversified portfolios, bonds also deliver something equities cannot consistently guarantee: contractual income and, in high-quality sovereign debt, a relatively defensive asset that can gain when economic growth falters and rates eventually decline.

The current bond selloff is thus not necessarily a reason to shun fixed income. It may be the very process that makes bonds attractive once more.

For investors who rode the equity rally in recent years, September's selloff serves as a reminder that portfolio building should not hinge solely on the best-performing asset class of the recent past. As inflation, fiscal risks, geopolitical strains and monetary policy grow less predictable, diversification becomes more valuable.

The key question for investors is no longer if bonds can beat stocks in every situation. It is whether, following this repricing, the income and diversification they provide are compelling enough to warrant a bigger allocation in portfolios.