Even as the world continues to reel from Donald Trump’s decision to withdraw from the Paris climate accord, another environmental disaster is already looming. In September, construction is scheduled to begin on a massive expansion of the Trans Mountain Pipeline, a project that will create a dramatic spike in planet-warming pollution by transporting oil extracted from Canada’s tar sands, one of the world’s dirtiest and most energy-intensive sources of crude. The supersize pipeline, stretching along a 715-mile route from Alberta to the Pacific Ocean, will pump 890,000 barrels of oil to the coast each day—more than doubling the current carbon emissions from tar sands. In climate terms, that’s the equivalent of putting another 3.6 million cars on the road.

Mining and processing oil from tar sands creates 14 percent more carbon emissions than the average oil used in the United States—and transporting it from the remote interior of Canada to foreign markets drives up emissions even more. Canada’s oil and gas industry is already the country’s largest source of carbon emissions, and it’s growing rapidly—up 76 percent between 1990 and 2015. James Hansen, one of the first climate scientists to sound the alarm on global warming, has warned that exploiting the tar sands would be nothing short of “game over for the climate.”

The pipeline itself is American, owned by Houston-based energy giant Kinder-Morgan, which boasts of operating a “giant toll road” for the flow of oil and natural gas. But the man paving the way for the pipeline is Prime Minister Justin Trudeau, who has carefully cultivated a reputation among environmentalists as the climate-conscious opposite of Donald Trump. “The pipeline flies in the face of a lot of the values we’re seeing from the prime minister—like his great statements about Canadians believing in climate action after Trump pulled out of Paris,” says Mike Hudema, a climate campaigner with Greenpeace Canada.

The Canadian government says it has factored Trans Mountain’s emissions into its plan to meet its obligations under the Paris agreement. But environmental experts argue that the math doesn’t add up. The new pipeline is projected to spew up to 17 million tons of carbon dioxide into the atmosphere every year—far more than Canadians can be expected to save by cutting back on emissions elsewhere. And the pipeline only makes economic sense if the Paris accord fails: After all, since tar-sand oil is more expensive to extract than light crude, Trans Mountain can turn a profit only if the world keeps burning more and more oil. By saying yes to the pipeline, Trudeau is effectively betting on a global spike in oil consumption. “Approval is predicated on the failure of the Paris agreement,” says Kathryn Harrison, a professor of political science at the University of British Columbia.

But the project’s timeline—let alone its ultimate completion—is far from assured. Trans Mountain has galvanized climate activists and indigenous leaders, who argue that the pipeline will pollute drinking water, injure wildlife, and displace native peoples. The city of Vancouver has filed a lawsuit to block the pipeline, arguing that the accompanying sevenfold increase in traffic by oil tankers poses a serious threat to aquatic life and water safety. Environmentalists say the impact on endangered orcas represents a violation of Canada’s Species at Risk Act; in an email to the New Republic, Kinder-Morgan notes that the government is requiring it to develop a Marine Mammal Protection Program to mitigate the potential threat to whales.