May’s Brexit catastrophe will define her – but her climate target will have the greater impact on British politics

In her desperation to leave a legacy, the prime minister has taken a small but significant step to a green future

The prime minister has come to life. After two years of unpleasant jibes about being a “dead woman walking”, she is now hyperactive, delivering strong, passionate speeches and trying to get things done.

Announcements from No 10 arrive in my email inbox more frequently now than during most of Theresa May’s time there. Most journalists hardly glance at them, more interested in the latest news from Sajid Javid’s team changing the time of his leadership campaign launch.

But the plan to legislate to set a net zero carbon target for Britain by 2050 has attracted attention. Is this a pledge to transform the economy, or is it simply a desperate attempt by a failed prime minister to leave some kind of legacy – any legacy at all?

It can be both. She has six weeks left in No 10 and so she has entered an accelerated farewell phase, a bit like Tony Blair’s last two years in office but compressed into a month and a half.

She must be acutely aware that she has failed in her central mission as prime minister, and has little to show for the last three years. And sceptics are entitled to point out that she has shown little interest in climate change in her time. Indeed, much of the momentum that has made the net zero target plausible was generated by the Labour government – one of Blair’s legacy issues was his effort to persuade George W Bush that the US should join the global effort to minimise climate change.

But that does not mean the amendment to Labour’s Climate Change Act 2008 is worthless. At the time, Conservatives complained that it was legislation by slogan, trying to write aspirations into law with no idea how they were to be delivered, and yet the decarbonisation of the UK energy sector since then has been spectacular.

Setting targets is effective: remember how the opportunists in opposition attacked Labour for them in the NHS, child poverty and schools, and rejoice that the sinners repent.

Even Greenpeace welcomed the net zero target: “Judging by the headline, this is a legacy Theresa May can be proud of.” Of course, its spokesperson went on to complain about the small print, pointing out possible loopholes and complaining that 2050 isn’t soon enough, but that is Greenpeace’s job.

Some of the criticisms that the Conservatives used to make of Labour grandstanding on climate change can still be applied to this target. It is all very well an outgoing prime minister setting ambitious goals, the Tories used to say: he cannot bind future parliaments.

It is true that, just as Theresa May can amend the Climate Change Act, so Boris Johnson – or whichever Dark Horse sneaks unexpectedly through the middle to seize the crown – could amend it back again. But these things usually operate like a ratchet: once a target has been set it becomes quite hard to unset it. At a time when public opinion is shifting in favour of more radical action on climate change, it will become difficult for a new prime minister to turn back the clock.

Theresa May is desperate for a legacy, and history will remember her for only one big thing – her failure to deliver Brexit – but let the footnotes record that she also took a small but significant step towards a greener future.