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 on Wednesday. "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's "Squawk Box Asia" when asked about the chances of a global economic recession.

Other economists appeared less worried about a recession, but shared Zandi's sentiment that growth would continue to weaken. Eswar Prasad, a professor at Cornell University, said consumer spending has helped support growth in several economies — even as momentum falters in other sectors. But that's not sustainable, he added. "Consumers and households cannot be counted on to keep growth going. So, really, the key is to come up with a set of policies that are going to spur a revival of business and consumer confidence, and end up boosting investments," he told CNBC's "Street Signs Asia" on Wednesday.

Monetary and fiscal support

On Tuesday, the International Monetary Fund made a downward revision to global growth. In its World Economic Outlook report, the IMF forecast that the global economy will grow 3% this year and 3.4% in 2020. That's lower than the 3.2% and 3.5% — for 2019 and 2020, respectively — that the fund projected in July.