Canada's medical professionals are presenting a solid front during the federal election campaign to urge political parties to take climate change seriously as a public-health issue.

"From a population health basis, it is the most critical problem that we're facing," Sandy Buchman, president of the Canadian Medical Association, said Thursday.

Buchman's group is one of 22 organizations to have signed an open letter to the parties. Others include the Canadian Nurses Association, the Royal College of Physicians and Surgeons, the College of Family Physicians of Canada, the Canadian Public Health Association and the Resident Doctors of Canada.

The groups represent 300,000 health professionals across Canada, including medical officers of health responsible for more than half the country's population.

Climate change is already having a big impact on public health, the letter says.

"We don't use words like climate emergency lightly," Buchman said. "We're using stronger language because we actually do feel the evidence supports it."

Insect-borne illnesses such as Lyme disease have already appeared in British Columbia, Alberta and Ontario where they never were before.

"About 2,000 Canadians a year suffer the impacts of that," said Robin Edger of the Canadian Association of Physicians for the Environment, which circulated the letter.

In Quebec, 66 people died in 2018's heat wave. Larger, more intense wildfires are causing greater respiratory problems as well as mental- health issues such as depression to substance abuse. Food insecurity is growing in the North as climate change makes hunting more difficult.

The World Health Organization lists climate change as the top health threat of the century.

Buchman — who works in palliative care for seniors and with the homeless — says the impacts fall hardest on the poor.

"These things affect vulnerable and marginal populations a lot greater than they effect the more well-to-do."

Yet the issue is usually only discussed in economic terms, he said.

"We haven't heard about the health impacts. That's the kind of attention that we want to bring to it."

The letter makes specific recommendations: Put a price on carbon. Set emission reduction targets that meet international promises and write a plan to meet them. Reduce greenhouse gases from the fossil fuel and agriculture sectors. Fund public transit.

"These have been developed over time and are felt to be the most impactful," Buchman said. "This is based on scientific evidence."

The letter says the world is running out of time. "By the time today's toddlers are in high school, our window for the most effective action will have closed."

A similar letter with the same recommendations — but with fewer signatories — was released in February. Edger said he was able to meet with all major parties to discuss it — except one.

"The Conservatives wouldn't meet with us," he said. Their party's platform doesn't include a price on carbon.

Edger said it wasn't difficult to get the different groups to sign the letter. "It was like pushing on an open door."

"This is one area where we can be unified, because the science is so good," said Buchman.

This report by The Canadian Press was first published Oct. 10, 2019.