This page opposes the building of a 1,700-mile pipeline called the Keystone XL, which would carry diluted bitumen — an acidic crude oil — from Canada’s Alberta tar sands to the Texas Gulf Coast. We have two main concerns: the risk of oil spills along the pipeline, which would traverse highly sensitive terrain, and the fact that the extraction of petroleum from the tar sands creates far more greenhouse emissions than conventional production does.

The Canadian government insists that it has found ways to reduce those emissions. But a new report from Canada’s environmental ministry shows how great the impact of the tar sands will be in the coming years, even with cleaner production methods.

It projects that Canada will double its current tar sands production over the next decade to more than 1.8 million barrels a day. That rate will mean cutting down some 740,000 acres of boreal forest — a natural carbon reservoir. Extracting oil from tar sands is also much more complicated than pumping conventional crude oil out of the ground. It requires steam-heating the sands to produce a petroleum slurry, then further dilution.

One result of this process, the ministry says, is that greenhouse gas emissions from the oil and gas sector as a whole will rise by nearly one-third from 2005 to 2020 — even as other sectors are reducing emissions. Canada still hopes to meet the overall target it agreed to at Copenhagen in 2009 — a 17 percent reduction from 2005 levels by 2020. If it falls short, as seems likely, tar sands extraction will bear much of the blame.