September ended with a warning from sovereign debt

The most consequential market development this week was not another record in artificial intelligence spending or another swing in oil. It was the message from the world's government bond markets. Investors are beginning to accept that the price of money may remain structurally higher than they had expected.

The adjustment has been abrupt. US two-year Treasury yields rose almost 60 basis points during September, their largest monthly increase since early 2023. On Thursday, the 10-year yield briefly reached 5.34%, its highest since 2002, after recording its largest quarterly rise since 1994. Britain's 30-year gilt yield climbed above 6% for the first time since 1998, while Japanese yields remained near multi-decade highs.

This is no longer simply a Federal Reserve story. Energy costs have revived inflation risks across developed economies just as the AI investment boom is supporting growth and capital demand. Australia's central bank illustrated the dilemma on Tuesday, raising its cash rate by 25 basis points to a 15-year high of 4.60%, its fourth increase this year.

Europe provided another warning. September inflation reached 3.4% in France, 4.1% in Italy, 3.3% in Germany and 5.0% in Spain. Markets are now pricing four further European Central Bank increases over the coming year.

What investors may have underestimated is that the energy shock is colliding with economies that remain surprisingly resilient. That combination is considerably less friendly to bonds than an inflation shock accompanied by recession.

The Fed has bought time, but inflation has not gone away

America complicated the picture this week because the data argued simultaneously for patience and vigilance.

Wednesday's personal consumption expenditure figures were softer than feared. Headline PCE inflation rose 0.3% in August and 3.4% from a year earlier, while core inflation increased 0.2% monthly and 3.0% annually. Consumer spending, however, surged 0.9%, while second-quarter GDP growth was revised up to an annualised 2.2%.

Thursday then delivered a reminder of the underlying price pressure. The ISM manufacturing index remained firmly expansionary at 54.5 in September, while new orders strengthened to 55.3. More strikingly, the prices-paid index jumped from 71.1 to 77.9.

The Fed nevertheless appears reluctant to follow September's rate increase immediately with another. New York Fed President John Williams said there was "no need for urgency", while Vice Chair Philip Jefferson argued that policymakers may need more time to assess the data. By Thursday, markets were pricing roughly a 25% probability of an October increase, down from around 70% earlier in the week, while a December move remained the dominant expectation.

That repricing helped Treasury yields retreat from Thursday's extremes, with the 10-year ending around 5.24%. Equities responded positively, although only modestly. Wall Street closed slightly higher after recovering from early losses.

The distinction matters. The Fed may pause in October, but that does not mean the tightening cycle is finished. Investors have merely shifted the timing.

Higher yields are becoming an earnings problem

For equities, the danger is less about whether the next Fed move comes in October or December than about where interest rates ultimately settle.

A sustained Treasury yield above 5% changes investment arithmetic. Future corporate cash flows are discounted more heavily, government bonds become a credible competitor for capital and refinancing becomes progressively more expensive. Companies can still deliver strong earnings in that environment, but investors have less reason to pay exceptional multiples for them.

AI makes the tension particularly interesting. The data-centre build-out is supporting manufacturing, investment and economic growth, yet it also requires enormous capital expenditure. If that investment raises productivity and free cash flow quickly enough, it can justify high valuations. If returns arrive more slowly while borrowing costs remain elevated, the hurdle rate facing those projects rises materially.

The same pressure eventually reaches households through mortgages and consumer credit, businesses through refinancing and governments through higher debt-servicing costs. That is why the long end of the bond market matters far beyond fixed-income portfolios.

Today's US employment report is the next immediate test. Economists expect roughly 90,000 additional non-farm jobs and unemployment to remain at 4.1%. But the bigger question extends well beyond one payroll number.

Markets spent much of the post-pandemic period waiting for interest rates to normalise downwards. September's bond rout suggests investors are reconsidering what normal means. If energy remains expensive, AI investment keeps growth firm and inflation proves difficult to return to 2%, the surprise of the next 6-24 months may not be another rate increase. It may be how long the world has to live with the yields already on the screen.

Sources and references

• reuters.com
• reuters.com
• reuters.com
• reuters.com
• reuters.com
• reuters.com
• reuters.com