Shell’s sale of dirty tar sands assets cleans up debt and spruces image

But campaigners remain unconvinced by firm's shift towards cleaner energy

When Shell sold most of its Canadian tar sands operations last week, the Anglo-Dutch oil company took a modest step towards making good on its promise to be part of the solution on global warming, rather than the problem.

Tar sands are reviled by climate change campaigners as one of the dirtiest forms of energy. The sands are a glutinous, bitumen-addled mix when extracted from the ground and a huge amount of energy is need to turn them into synthetic crude oil.