Hundreds of thousands across the country packed city streets in a call to halt climate change.

Floods, heatwaves, and erratic winter weather are among the signs experts say global warming is a reality.

Kregg Hetherington is a lead researcher on Montreal's waterways and doesn't think Montreal is prepared for the effects of a warming planet.

"I don't think anybody is, to be honest," he said. "People already know that in the last few years we've seen kinds of flooding in Montreal that we've never seen before. That's one of the obvious effects of climate change coming, and in order to be able to change a city to be able to deal with that kind of thing takes huge investment in infrastructure, but also huge social rethinking of what our relationship is with the natural environment, water and everything else that comes with it."

He said one area the city needs to look at seriously is the massive system of pipes underground that channel water from the many streams and rivers that once existed on the island. Building bigger pipes is the most common response to increased water levels, but Hetherington said bringing water to the surface is another, more progressive way to deal with it.

"Having more water is going to have a good effect on temperature, it brings more animals to the surface, (and) it helps you think about your relationship to the natural world in a different way that is a little bit hard in this concrete block right now," he said.