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

Businesses will lead the world out of the climate crisis, Gore said in an optimistic speech on the final day of the Climate Summit of the Americas.

Cheap energy, he said, allows businesses around the world to finance their operations. The renewable energy sector is a rapidly growing market, Gore added.

"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, the Caribbean is also in a drought and wildfires across western Canada and the United States shows society something is wrong.

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

After the 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.

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

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

Former Mexican President Felipe Calderon was scheduled to speak Thursday afternoon.