Climate change will cost Canada about $5 billion a year by 2020, a startling new analysis commissioned by the federal government warns.

Those costs will continue to climb, to between $21 billion and $43 billion a year by the 2050s, the report estimates. It all depends on how much action is taken to cut global greenhouse-gas emissions, as well as how fast the population and the economy grow too.

In the worst-case scenario, climate change could cost as much as $91 billion per year by 2050.

The report was issued Thursday morning by The National Roundtable on the Environment and the Economy. Its members are business leaders, academics and researchers who were chosen by the federal government to advise them on how to handle the climate change crisis, while also continuing to stimulate the economy.

In its report, the think-tank projects the cost of climate change based on four scenarios, ranging from slow population and economic growth combined with low climate change, to rapid population and economic growth and high climate change.

Though the researchers came up with a range of estimates, they point to the same conclusion: the longer the effects of climate change are ignored, the costlier they become.

"Climate change will be expensive for Canada and Canadians," the report states.

As the Earth warms over the next few decades, it will have a number of economic effects on Canada, the group says.

Polar ice caps are expected to melt and sea levels to rise, leading to an increase in flooding and storm surges. The resulting flood damage could cost between $1 billion to $8 billion a year, the report estimates, with higher-than-average impacts in Atlantic Canada.

Climate change will also cause havoc to the country's timber industry, the group predicts. By the 2050s, the changes in pests, fires, and forest growth are expected to cost the Canadian economy between $2 billion and $17 billion per year.

Poorer air quality from higher temperatures will lead to more hospital visits, resulting in millions of dollars in costs to local health care systems for at least four of Canada's major cities: Toronto, Montreal, Vancouver and Calgary. In Toronto alone, the illnesses associated with the impacts on air quality will cost the health care system between $3 million and $11 million per year by the 2050s.

The report concludes that if Canada wants to keep the costs of climate change in check, it will have to work to reduce global greenhouse gas emissions and invest in ways to manage the impacts to come.

The study found that many adaptation strategies are easily worth their costs, including:

• improving forest-fire protection by planting resilient trees and actively controlling pests
• banning new buildings in areas at risk of flooding
• installing pollution control technologies to limit ozone formation

Other initiatives, on the other hand, might help to reduce greenhouse gas emissions, but would come at a high cost, including replacing conventional roofs with green roofs in cities.

The group also warns that while many of the costs of adaptation can seem large at the outset, the cost of not adapting could be more expensive.

"The highest costs result from a refusal to acknowledge these costs and adjust through adaptation," the report concludes.

"Once the benefits of adaptation are incorporated, adaptation can often lead to greater savings than costs."