Government bond yields across the G7 have surged following the COVID-19 pandemic and Russia's invasion of Ukraine, as central banks raised interest rates aggressively to tame surging inflation.
Elevated longer-term borrowing costs also reflect that investors want better returns to compensate for the risk of holding the debt.
A surge in borrowing by AI "hyperscalers" is an added pressure, as buyers demand higher returns to keep purchasing the flood of bonds hitting markets.
The difference between shorter and long-dated government bond yields has increased sharply, making it relatively more expensive to borrow for longer.
The pressure is being intensified by fiscal concerns, central banks reducing bond holdings and some big traditional investors in long-term debt such as insurers and pension funds reducing their purchases from Japan to Britain.
To mitigate the impact, many governments have started selling bonds with shorter maturities. But that's risky too because they have to repay or refinance the debt sooner, so any rise in yields feeds faster into interest costs.
Debt is roughly equal to or higher than economic output across the G7 bar Germany, Europe's biggest economy.
The 2008 global financial crisis, the 2011-12 euro zone debt crisis and the 2020 pandemic all increased debt levels, hurting growth. More recently, the Russia-Ukraine war, the Iran war and extreme heat have added to spending needs.
Japan has the highest level, with debt more than double its output, while even Germany, once a champion of austerity, is ramping up its borrowing. Germany's finance ministry told Reuters that Russian aggression was driving up funding needs for massive defence investment, pushing borrowing costs higher.
Ageing populations, interest bills and increased spending on defence and climate change could raise debt levels further.
Higher post-pandemic borrowing costs are feeding into governments' interest payments.
While well below historical peaks for many countries, interest payments as a share of output have risen steadily across most G7 countries recently, notably in the United States.
In fact, interest payments across OECD countries, including the U.S., already topped defence spending in 2024.