A U.S. activist derided by Canadian Energy Minister Joe Oliver this week over his opposition to the Keystone XL pipeline says Canada's government is a "Neanderthal" on climate issues, in an interview airing Saturday on CBC Radio's The House.

James Hansen, a former NASA scientist who has been a vocal opponent of Alberta's oilsands and the proposal for a pipeline to carry oilsands crude to the Texas Gulf coast, was reacting to Oliver's characterization of his arguments as "nonsense" during a visit to Washington this week.

"Well, the current government is a Neanderthal on this issue," Hansen told host Evan Solomon.

Hansen said Canada can still be a leader on the carbon emissions issue, pointing to British Columbia's carbon tax and adding that Canada has in the past "been ahead of the U.S. on environmental issues."

Hansen said the science of climate change is "crystal clear."

"But ... many of the governments are denying and trying to ignore what's going to happen a few decades downstream. They're only worried about the next two or three years."

Listen to James Hansen's full interview with Evan Solomon on The House, Saturday at 9 a.m. on CBC Radio One and watch it here at CBC.ca.