With more than half of G20 members attending -- representing most of the world's largest economies -- "this first gathering of its kind aims to further galvanize global momentum for the implementation of the Paris Agreement," the European Commission said.
Prime Minister Justin Trudeau of Canada, who will make a brief appearance at the Montreal talks, will again stand apart from US President Donald Trump on this issue and resolutely commit Canada to reduce its carbon footprint, Canadian officials have said.
When Trump chose to withdraw the United States from the Paris accord, Canada, China and the European Union immediately reaffirmed their respective commitments to the climate pact, and in July the G20 called the accord "irreversible."
Nearly 200 countries agreed in Paris at the end of 2015 to limit or reduce carbon dioxide emissions with the aim of keeping the rise in average global temperatures to no more than 1.5 degrees Celsius by 2050, compared to preindustrial levels.
On the eve of the Montreal conference, Europe's top climate official Miguel Arias Canete said the EU continues to press for "full and swift implementation" of the accord, noting that progress has been made toward finalizing details of its plan to reduce European emissions by 40 percent by 2030.
Despite being the world's sixth-largest oil producer, Canada is "committed to its international climate obligations," said the environment ministry.
It hopes to reach its climate goal by massively investing in "clean energy" technologies, a spokeswoman added.
US stance a setback
Key player China and its special representative Xie Zhenhua will bring to the table a potentially major advancement in transportation. China, along with Britain and France, has announced its intentions to ban petrol and diesel cars starting in 2040. This would bring a huge drop in air pollution in the world's largest car market.
And in a speech in Strasbourg on Thursday, European Commission President Jean-Claude Juncker reaffirmed the EU's aim of being "at the forefront of the fight against climate change."
The US dealt that fight a major setback when Trump pulled the world's biggest economy out of the Paris accord in June.
To bolster the EU position, Juncker promised to soon put forth a proposal to reduce carbon emissions in the transportation sector.
Catherine McKenna, Canada's environment minister, will meantime press her counterparts and multinationals chief executives to develop solutions for "a low-carbon, climate-resilient economy."
Holding the meeting in Montreal is not coincidence. It is here that negotiations led to the first international agreement on the environment 30 years ago, with a ban on ozone-depleting gases.
In addition to Canada, the EU countries and China, nations including Russia, India, Mexico, Brazil, Indonesia, South Africa, South Korea and Turkey will be represented by senior ministers.
With only 50 days before the next United Nations Conference on Climate Change (COP23), some of the low-lying nations hardest hit by the effects of climate change (the Marshall Islands, Fiji, Maldives) and some of the poorest (Mali and Ethiopia) will also be present.