PHOTO: AFP/FILE

REUTERS, Tinos

Government borrowing is unsustainable in the United States and much of Europe. There is also huge pressure to increase spending on climate, defence and ageing populations. Some mixture of higher taxes and inflation will ultimately be unavoidable.

Global public debt as a percentage of output has been rising almost without a break since the mid-1970s. It will reach over 100 percent of GDP by 2030, the highest level since World War Two, according to a forecast by the International Monetary Fund.

The problem is that governments are spending more than they are raising in taxes. Borrowing can only be sustainable if it is stable or falling as a percentage of gross domestic product. But that is only true if the annual budget deficit as a proportion of output is equal or less than nominal growth - an economy’s growth rate before adjusting for inflation.

Among the Group of Seven rich countries, the United States, France and the United Kingdom have the biggest problems. Their governments’ deficits are forecast to be 7.4 percent, 5.4 percent and 4.3 percent of GDP this year respectively, according to the IMF. Meanwhile, their economies’ sustainable nominal growth rates are probably no more than 4 percent, assuming both growth and inflation of 2 percent. With debt at 121 percent, 113 percent and 101 percent of GDP respectively in 2024, something will have to change.

The other G7 countries’ debts are not on an upward path because their annual deficits are more or less under control. But Japan’s debt at 237 percent of GDP and Italy’s at 135 percent are uncomfortably high. Only Germany and Canada are in reasonable shape.

An unsustainable debt load does not necessarily lead to a financial crisis. Rich countries typically have a lot of rope with which to hang themselves. This is especially true of countries which print their own currencies, such as the United States, the United Kingdom and Japan. It is less so of France and Italy, which must live by the monetary policy set by the European Central Bank.

But even if the day of reckoning is not round the corner, borrowing cannot rise forever. The problem is that there are few easy ways to bring it under control.

The best option would be to increase growth. But unless artificial intelligence provides a miraculous boost to their economies, rich countries seem more likely to slow down in the coming years - not least because US President Donald Trump is undermining the world trading system with his tariffs.

Another option is to cut government spending. But there is massive public resistance to this. Just look at how France is unwilling to put up the age at which its citizens receive pensions.

In fact, “structural headwinds” could boost public spending by around 3 percent of GDP in coming years, according to Erik Nielsen, senior advisor at Independent Economics.

The biggest items are ageing populations which push up pension and healthcare costs, defence spending, climate-related outlays, and infrastructure.