They know a conservative government has no plans to do anything at all about climate change. A CPC government will not just prevent progress, but actively accelerate climate change. Pierre was part of Harper's government, who did such a bad job (sector by sector regulatory approach, repeat) that Canada was on track not only to miss our targets , but also start increasing our GHG output. If it wasn't for electing Trudeau in 2015, we'd still be on that path and the thing about conservatives is they're perfectly willing to put us back on it.