Global bond markets are sending an increasingly clear warning to governments; persistent fiscal deficits, rising debt loads and geopolitical shocks are pushing long-term borrowing costs higher, threatening to squeeze households, companies and financial markets.
From the United States and Japan to Germany, France and the UK, long-term government bond yields have climbed to multi-year or multi-decade highs in recent weeks.
The moves have come as the prolonged U.S.-Iran conflict has pushed oil prices higher, while investors have also grown increasingly concerned about the amount of debt governments need to issue.
The U.S. 30-year Treasury yield climbed above 5% earlier this week to its highest level since 2007, while Japan's 10-year borrowing costs approached 3%, a level not seen in three decades.
Germany's 10-year Bund yield reached its highest since 2011, while French yields climbed to their highest since 2008.
The pressure is particularly significant in the U.S., where outstanding public debt has surpassed $40 trillion.
At the same time, technology companies are borrowing heavily to fund the construction of artificial intelligence data centres and related infrastructure, increasing competition for available capital.
The Iran effect
The now six-month-old Iran war has increased uncertainty for the bond market as hopes for a diplomatic breakthrough have faded, while disruption around the Strait of Hormuz has pushed energy prices higher.
Brent crude has moved back above US$90 a barrel, reinforcing concerns that a prolonged conflict could keep inflation elevated and delay interest-rate cuts.
That has increased the pressure on longer-dated bonds, whose yields reflect expectations for future growth, inflation and government borrowing as well as central-bank policy.
Yet the recent rise in yields cannot be explained by inflation expectations alone.
ING analysts Padhraic Garvey and Benjamin Schroeder argue that the biggest driver has been an increase in U.S. real yields.
They estimate that practically all of the rise in the 10-year nominal Treasury yield over the past six months has come from higher real yields, rather than a comparable increase in inflation expectations.
Before the Iran war, the U.S. 10-year real yield was around 1.7%. It has since risen to about 2.4%, which ING considers much closer to historically normal levels.
The bank estimates that a U.S. 10-year nominal yield of around 4.5% represents a normal level, with the market currently trading above that threshold.
That distinction matters because it suggests investors are demanding greater compensation for holding long-term debt even without a major deterioration in expected inflation.
Fiscal fears take centre stage
Developed economies are running large budget deficits, while governments face rising debt-servicing costs and continued borrowing requirements.
Higher yields then create a feedback loop: as borrowing costs rise, governments need to allocate more money towards interest payments, potentially requiring further borrowing.
Reuters reported that the New York Fed estimates the term premium on 10-year Treasuries - the additional compensation investors require to lend to the government for a decade - at around 80 basis points, close to its highest level in 12 years.
The U.S. 10-year yield was around 4.71% on 18 August, with the 5% level increasingly in focus.
The consequences extend well beyond government finances. Sovereign bond yields form the benchmark for a wide range of borrowing costs, including mortgages, corporate loans and other consumer credit.
As yields rise, companies face more expensive financing while households can face higher mortgage and lending rates.
The impact is already visible in financial markets, with higher bond yields putting pressure on equities, particularly growth and technology stocks whose valuations are more sensitive to changes in discount rates.
AI creates another source of demand for capital
The artificial intelligence investment boom is adding to the pressure.
Technology companies and AI infrastructure operators are borrowing vast amounts to build data centres, expand electricity capacity and develop the computing infrastructure needed to support increasingly sophisticated models.
Analysts cited by Reuters noted competition for capital from AI hyperscalers as one factor exacerbating the government bond sell-off.
ING, however, takes a more measured view. While acknowledging that AI-related long-duration debt issuance has increased dramatically, its analysts argue that strong demand for corporate credit means the surge in technology borrowing is not the primary explanation for higher Treasury yields.
Instead, they point to persistent fiscal deficits across developed economies as a more important and durable source of pressure.
Carl Weinberg, founder of High Frequency Economics, offered a different assessment, arguing that AI infrastructure spending is competing directly with governments for the world's pool of savings.
"The build-in of AI infrastructure, the investment in technology, the investment in utilities and so forth — that’s borrowed a lot of money," he said, according to CNBC. Weinberg estimated that as much as $600 billion may have been borrowed for AI development over the previous year, with another $200 billion of funding, borrowing, new issuance and IPOs already in the pipeline.
The result, he argued, is a new "hyper borrower" in the form of the "collective AI enterprise", competing with governments and other businesses for capital.
Treasury steps in
The sharp rise in long-term yields prompted the U.S. Treasury to intervene this week.
Treasury Secretary Scott Bessent announced that the department would double the size of its planned buybacks of 10- to 30-year Treasury securities to at least $4 billion per operation, up from $2 billion. The programme will run from 9 September through 4 November.
The move followed a spike in the 30-year Treasury yield to 5.34% on Tuesday, its highest level since 2007.
Following the announcement, the yield fell to around 5.18%, while the 10-year yield declined by roughly six basis points to 4.66% on Wednesday.
The Treasury said the larger buybacks were designed to provide greater liquidity to longer-dated bonds, where it said there was strong investor demand.
But the intervention does not address the fundamental problem of rising government debt.
The scale of the intervention is also relatively small. The additional $2 billion per operation is tiny compared with the roughly $32.2 trillion Treasury market and around $5.5 trillion of outstanding 20- and 30-year bonds.
ING similarly argues that the buybacks are unlikely to change the underlying direction of long-term yields. The bank said the timing of the announcement was important because the Treasury had only set its quarterly buyback schedule two weeks earlier, suggesting the decision was at least partly intended to reassure markets that officials were monitoring the rise in long-term yields.
Bessent and Warsh face a policy dilemma
The Treasury intervention has also raised questions about the relationship between fiscal and monetary policy.
Federal Reserve Chairman Kevin Warsh has emphasised the importance of allowing markets to determine the appropriate level of long-term borrowing costs, while maintaining a focus on bringing inflation back to the Fed's 2% target.
Warsh led a 9-3 decision in July to leave the policy rate unchanged. He has also expressed scepticism about using the Fed's balance sheet to influence long-term yields and has made reducing the central bank's $6.8 trillion balance sheet a key objective.
Bessent, meanwhile, has argued that the Treasury and Fed could work together if there were changes to the central bank's balance sheet, while insisting that the buyback programme is separate from monetary policy.
"Part of it is signaling here, and to show that we believe that the yields don't reflect the underlying fundamentals," Bessent reportedly said in a CNBC interview.
The contrast creates a difficult policy dynamic. Treasury intervention aimed at lowering long-term yields can ease borrowing costs, but aggressive Fed purchases of long-term securities could resemble monetary easing at a time when inflation remains above target.
Why Main Street should care
The bond sell-off is ultimately less about traders watching yield charts and more about the cost of money across the economy.
Long-term Treasury yields feed directly into mortgage rates and corporate borrowing costs. A sustained rise therefore risks keeping housing unaffordable, increasing financing costs for businesses and weighing on investment.
That creates a difficult trade-off for policymakers. Allowing yields to rise can help impose discipline on governments and reflect the market's assessment of inflation and fiscal risks. But an uncontrolled increase can tighten financial conditions across the economy and undermine growth.
The problem is particularly acute when governments are already running large deficits. Any shock - from higher oil prices to weaker growth or geopolitical instability - can cause investors to demand greater compensation for holding long-term debt.
The recent bond sell-off may eventually prove self-correcting. Higher yields can attract investors who had previously been unwilling to lock in capital at lower rates, eventually restoring demand for government debt and pushing yields back down.
But the risk is that the market has entered a more volatile era in which governments can no longer assume that there will always be sufficient demand for their debt at historically low borrowing costs.
For the U.S., the 5% threshold on the 10-year Treasury yield is therefore becoming an important psychological and financial marker. A sustained break above it could further tighten financial conditions, pressure equities and raise questions about the sustainability of government finances.
Treasury buybacks may buy policymakers some time, but they cannot resolve the underlying imbalance between government spending, revenues and debt issuance. As the global bond market increasingly asserts itself, governments may find that fiscal discipline is no longer simply a political choice - it is becoming a condition imposed by investors.
