One expert has delivered a grim outlook for share markets around the world. 

Stocks have tumbled after US President Donald Trump slapped tariffs on Canada, China and Mexico. 

Infometrics Chief Forecaster Gareth Kiernan says markets surged after the election with thoughts that Trump might promote growth. 

He says there might not be a quick fix for the issue. 

"I suspect it's going to be something that could last a lot longer, and we could be in a more serious downward trend that lasts for up to 12 months."

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