Extinction Rebellion seems to have cracked using protests to transform public debate. But as it starts another major rebellion this week, it might find the challenge ahead is even greater.

Extinction Rebellion’s April protests were an enormous success. Together with the BBC’s Attenborough documentary and the school climate strikes, they created a surge in public concern about the environment. The climate emergency is now established in the top five most important issues facing the UK today, at around the same level as the economy. Since the April protests, the government has legislated for net-zero greenhouse gas emissions by 2050 and Labour is moving towards a much more ambitious target.

Few people could have predicted that a two-week blockade of central London would be met with so much support or have such political impact. So the natural question is whether a new round of protests can repeat the success.

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The fact this month’s rebellion won’t be such a novelty could make things harder. It’s the difficult-second-album problem: repeat your material and you’re boring; innovate and you may lose the magic. And with the police preparing to move faster against protesters this time, it’s inevitable that opponents of climate action will call for tougher law enforcement.

But difficult though it will be for the protests to recapture the novelty and public support of the April protests, that is far from the biggest problem. Ironically, the greatest threat to the movement is its apparent success over the past six months. If the public believe the protesters have already won, continued street blockades could look unnecessary.

It’s here that public opinion turns from being helpful to being a problem for Extinction Rebellion. The overwhelming majority want action to limit climate change and support a net-zero target; most even support bringing that target forward from the government’s current date.

Play Video Extinction Rebellion protesters stage 'die-in' outside London fashion week venue – video

But most people’s attention stops there. Few people pay attention to the details or punish politicians who don’t have a plan. This means there’s not much incentive for politicians to go beyond simply pledging to tackle the climate crisis with ambitious-sounding targets.

Take the government’s net-zero law. It would just about make the UK compliant with the Paris agreement’s goal of avoiding dangerous warming (although it is too slow for that if you consider the UK to have a responsibility to clean up faster than less- affluent countries). But the government wasn’t even on course to meet its old, weaker target; we are nowhere near meeting the new one.

Or take Labour’s conference motion to meet the net-zero target by 2030. This is close to Extinction Rebellion’s demand, but the party shouldn’t get much credit for environmental saviourhood until it shows how it would deliver. Scrapping its support for Heathrow expansion will be hard enough for Labour – with the party’s union funders firmly behind more tarmac and more planes – and that would be among the simplest of the policy switches needed to decarbonise in 11 years.

So apparent allies of the protesters can actually be a threat to faster climate action. Emission-cutting pledges can be useful – but if they aren’t combined with a plan they can undermine the cause by making it seem like the battle has been won. The next wave of Extinction Rebellion protests will be a success if it forces climate-friendly politicians to show their proposals. When a politician says they will stop the climate crisis from escalating, the first question that needs to be asked is: “how?”

Answering that question requires politicians to expose the fact that avoiding dangerous warming will be disruptive and difficult. Many people will look for reasons to find a way out and so the debate may return to “why?” But this is Extinction Rebellion’s specialist subject: its explanation of the climate emergency may be terrifying but it is well-evidenced.

This challenge – to force apparently “green” politicians to come with a plan – is daunting. But few people would have imagined that a climate change protest could occupy central London and be met with widespread public backing. The protesters might just be the people who can do it.

• Leo Barasi is the author of The Climate Majority: Apathy and Action in an Age of Nationalism, published by New Internationalist