The problem is, that really doesn't prove what he wants it to prove.
As an aside, he shows himself in the same article to have a very shaky grasp of numbers: he says "This oddball rabble are five times bigger than the Lib Dems, despite getting only 13 per cent more support." What he means is that the Tories got more votes than the Lib Dems by an amount of 13% of the total votes - in fact the Tories got 56% more votes than the Lib Dems did. That is the only ratio that it makes any sense to compare with the sizes of the respective parliamentary parties. He could also say that the Tories got 38% more of the seats in the Commons despite getting only 13% more of the votes in the country. Using the correct 56% number rather than the irrelevant 13% wouldn't have weakened the reasonable point Hari was making, but it proves he is either habitually dishonest even where it doesn't help him, or very stupid indeed.
Back to the 91%, then, assuming we can in this instance trust Hari to report a percentage accurately. I have just checked the Conservative Manifesto:
We will reduce UK greenhouse gas emissions and increase our share of global markets for low carbon technologies.
Labour have said the right things on climate change, but these have proved little more than
warm words. Despite three White Papers, a multitude of strategies and endless new announcements, the UK now gets more of its energy from fossil fuels than it did in 1997
If 91% of the candidates who successfully ran for election under that manifesto do not believe in man-made Global Warming, what it proves is that politicians' positions on climate change bear no relation to what they actually believe to be true.
It further proves that man-made global warming is a politically convenient position - one that politicians find it advantageous to adopt, even if they don't believe it.
This is tremendously important, because it is the positions taken by politicians that have set the public scene. It is politicians who have set up and maintained the IPCC, set the priorities of NASA and the Met Office, and form the context for any public debate. And those politicians are under pressure to pretend to believe in man-made Global Warming, even when they don't.