The U.S., Mexico and Canada are expected to pledge on Wednesday to collectively generate 50 per cent of their electricity from zero-carbon sources by 2025, according to White House officials…The agreement is expected to be struck at the North American Leaders’ Summit in Ottawa…Wednesday’s agreement will put all three countries on a path to meeting their climate goals, though it won’t be enough by itself, said Michael Mann, a Penn State University climatologist…For example, hydropower reservoirs often emit methane — a powerful greenhouse gas helping to drive climate change. California does not consider large hydropower projects to be a renewable power source.“Wind and solar are arguably preferable choices from a full environmental cost-accounting standpoint, but such matters are worthy of a robust policy debate,” Mann said.

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