TORONTO -- Former U.S. vice-president Al Gore and former Mexican president Felipe Calderon say fighting climate change will be a boon to the global economy, despite critics' fears that abandoning fossil fuels will cripple world markets.

On the final day of the Climate Summit of the Americas both tried to dispel the notion that society must choose between economic growth and helping the environment.

"We're seeing in some of the states and provinces reductions in (carbon dioxide) emissions accompanied by economic growth surging," Gore told a crowd of hundreds of invitation-only delegates in attendance.

"Places like B.C., California, Quebec and Ontario."

Calderon, now chair of the Global Commission on the Economy and Climate, echoed Gore's thoughts, saying his organization's research shows economies can grow while at the same time reducing greenhouse gas output.

"Sweden increased more than 50 per cent its economic growth and reduced almost 25 per cent its carbon emissions related to 1990," he said.

"For the first time in 40 years at the global level, the GDP of the world increased almost three per cent and the emissions didn't grow -- in other words we started to decarbonize the economic growth."

Calderon said societies need to fundamentally change their systems, from getting away from fossil fuels, to ending deforestation, to building better cities and retrofitting aging infrastructure to make them more environmentally friendly.

Earlier in the day, Gore drove his point home in an optimistic speech that only briefly touched on severe weather and natural disasters.

"The thrilling news is the cost of renewable sources of energy is plummeting much faster than anyone expected they would," he said.

The economy is already converting to one with an environmental focus and costs for alternative energy sources such as solar and wind energy will continue to drop, he said.

Gore laid out his speech in three parts to explain the climate crisis, answering yes to his own questions: "Must we change? Can we change? Will we change?"

"You can go around the world and see that Mother Nature is sending us very clear messages," he said.

He said 99 per cent of California is in a drought, as is much of the Caribbean and wildfires across western Canada and the United States shows society something is wrong with the planet.

"It is striking isn't it that every night on the television news is like a nature hike through the Book of Revelation?"

Gore said moving to an environmentally focused economy will be a lot of work. For example, he said, old buildings need to be retrofitted by installing solar panels and energy-saving windows.

All that work "provides jobs, lots of jobs," he said.

"And they're the kind of jobs that can't be done by robots -- at least not yet."

After Gore's talk, Ontario Premier Kathleen Wynne and 21 other subnational states signed a climate action statement that commits to supporting carbon pricing, meet greenhouse gas reduction agreements and ensure public reporting.

Quebec, Newfoundland and Labrador, Manitoba, California and Vermont are among those who also signed the statement along with several regions in Brazil and Mexico.

On Wednesday, Quebec joined Ontario and California and other subnational states after Premier Philippe Couillard signed a memorandum of understanding in a pledge to keep warming at or below two degrees Celsius by 2050.

The leaders emphasized the role subnationals, such as provinces and states, can play in reducing greenhouse gas emissions.