LONDON (Reuters) - Global economic growth is slowing, according to the International Monetary Fund, policymakers and hundreds of economists polled by Reuters - but that downturn is coming at a time when central banks’ arsenals are running on empty.

FILE PHOTO: The International Monetary Fund (IMF) headquarters building is seen ahead of the IMF/World Bank spring meetings in Washington, U.S., April 8, 2019. REUTERS/Yuri Gripas/File Photo

On Tuesday, the IMF cut its expectations for world growth to its lowest level since 2016, its third downgrade since October, and said risks to the global financial system have grown over the past six months.

“This is a delicate moment for the global economy,” IMF chief economist Gita Gopinath told a news conference.

Major central banks have reined in their forecasts, and in recent months economists in Reuters polls have repeatedly trimmed their expectations for the countries they cover.

“Last week’s releases provide some reassurance that the world economy is not falling off a cliff, which had seemed a plausible, if relatively small, risk as recently as a month or so ago. This is clearly good news,” said Neil Shearing, group chief economist at Capital Economics.

“But we remain in the late stages of this global economic expansion. Springtime inevitably brings with it an air of optimism for the future – but in the case of the world economy at least, we expect growth to remain subdued.”

Rising trade protectionism and tighter financial conditions have been blamed for the slowdown. Uncertainty over how to practically implement Britain’s June 2016 decision to quit the European Union has also played its part.

Trade conflict with the United States and sluggish demand means China’s economic growth is expected to slow to a near 30-year low of 6.2 percent this year, a Reuters poll showed on Friday.

While still waging a trade war against China that is widely regarded as harmful to global growth, U.S. President Donald Trump has now threatened to slap tariffs on $11 billion of products from the EU.

Those threats come as British politicians continue to struggle to agree on a way to leave the EU. A messy exit would almost certainly further damage the economies of both sides in the divorce, with the impact likely spreading further afield.

In the early hours of Thursday, EU leaders gave Britain six more months to leave the bloc. But the latest extension still offers little clarity on when, how or even if Brexit will happen.

British Prime Minister Theresa May has so far failed to build support in the UK parliament for the withdrawal terms she agreed with the EU last year, but she now has until Oct 31 to do that or find an alternative course.

“Brexit was originally supposed to have occurred two weeks ago but the intractability of the problem coupled with political incompetence on the part of the UK means that it has been postponed yet again,” said Peter Dixon, an economist at Commerzbank.

“The scope for lifting Brexit-related uncertainty is thus limited, which suggests little prospect of a sustainable rebound in either the economy or sterling.”

THE CUPBOARD WAS BARE

What appears to be a globally synchronized economic slowdown comes as central banks run out of tools for supporting growth.

After the 2008 financial crisis policymakers slashed interest rates - sometimes below zero - and also turned to more unconventional measures to boost growth, such as pumping trillions of dollars into economies.

But as inflation has never really picked up, many of them have yet to change tack and start tightening.

The U.S. Federal reserve led the pack and has hiked rates nine times in the current cycle, but it is probably now done with increases until at least the end of next year.

The Bank of England has lifted Bank Rate twice since the June 2016 referendum, but borrowing costs remain very close to record lows and expectations for a rate hike later this year are far from set in stone.

The European Central Bank, already on its longest break from changing interest rates, may have missed its chance to raise them this time around altogether. According to a median forecast in a Reuters poll, the first increase won’t come until after June next year.

On Wednesday, ECB President Mario Draghi even raised the prospect of more support for the struggling euro zone economy if its slowdown persisted, saying the central bank had “plenty of instruments” with which to react.

However, one problem is that after pushing borrowing costs to record lows and taking 2.6 trillion euros’ worth of bonds out of the market, the ECB’s options are limited and there are fears what it has will not be enough.

“Market pricing is expressing more anxiety that the ECB is either too slow to use whatever is left in its policy toolbox or – worse – that it thinks the tools won’t do much anyway,” said Laurence Mutkin, global head of G10 rates strategy at BNP Paribas.