The last time a Conservative leader decided to push environmental concerns to the top of the political agenda, a great many things were different. She was Prime Minister, after all, and David Cameron is not.
But Cameron is setting the political agenda in the UK in a way that no Conservative leader since Thatcher has succeeded in doing. And the choice of green issues is a smart one. It is, of course, all about healing the Conservative brand. It is about getting more people to vote Conservative. He wants the Party to be consistently above 40% in the polls.
But there are tactical factors too. Whether 40% is a winning or a losing total depends on how the rest of the votes are distributed. Last time environmental concerns rose up the agenda the Green Party scored 15% in the 1989 Euro-elections. Of course, the Liberal Democrats were in a mess at the time, and the Greens took a great many votes that would otherwise have been theirs. But with people already speculating that Ming Campbell may not see another party conference season, perhaps that situation will recur.
There are Labour voters who are deeply disillusioned: Clare Short being an obvioius example. Some of them could never bring themselves to vote for the Lib Dems, though others might. What if the Green vote started to pick up. It seems to me that they would take some votes from Labour and some from the Lib Dems. Others, of course, would be people who otherwise might not vote.
Could it lead to the Lib Dems crashing as it did in 1989? That seems unlikely, but possible. Could the Greens take 5% each from Labour and the Lib Dems? Sure they could. From Cameron's point of view, where is the downside?