There’s an “uncomfortably high” chance that a recession could hit the global economy in the next 12-18 months — and policymakers may not be able to reverse that course, an economist said.

“I think risks are awfully high that if something doesn’t stick to script then we do have a recession,” said Mark Zandi, chief economist of Moody’s Analytics. “I’ll say this also: Even if we don’t have a recession over the next 12-18 months, I think it’s pretty clear that we’re going to have a much weaker economy.”

Avoiding a slowdown in economic activity requires many factors to “stick to script” at the same time, he said. That includes U.S. President Donald Trump not escalating the tariff war with China, the U.K. finding a resolution to Brexit and central banks continuing their monetary stimulus, Zandi explained.

“I think high, uncomfortably high,” he told CNBC when asked about the chances of a global economic recession.