OTTAWA—The Supreme Court of Canada says the federal carbon price is entirely constitutional. The split decision upholds a pivotal part of the Liberal climate-change plan that accounts for at least one-third of the emissions Canada aims to cut over the next decade. Chief Justice Richard Wagner says in the written ruling that climate change is a real and existential threat to Canada and the entire world, and evidence shows a price on pollution is a critical element to addressing it. Wagner also says provinces can’t set minimum national prices on their own and if even one province fails to reduce their emissions it could have an inordinate impact on the rest of the country. It is a split decision with six judges entirely in favour, one partial dissent and two entirely in disagreement with the majority. Canada implemented the Greenhouse Gas Pollution Pricing Act in 2019 setting a minimum price …