So what have we learned? Decarbonising the electricity supply can be done with a mixture of renewables and maybe a dash of nuclear. Decarbonising domestic heating is the biggest challenge and will cost half a trillion pounds.

The technologies we need to do it already exist and there’s every chance that new better ones will emerge. As we move towards 2050, successive governments will have to back several horses to make sure it’s not locked into any one path. Some of those bets may fail.

The task, then, is daunting but not impossible. But there are some inconvenient truths that this analysis and the targets the government has set ignores.

Firstly, international aviation is not included in the net zero target. It’s estimated that the UK’s share of aviation may make up as much as 7% of the UK’s total emissions.

And secondly, the way we currently measure emissions does not include the environmental cost of the goods we import.

If the UK were to close down a carbon-hungry steel plant, our emissions would go down. But we still need steel so we would import it - from China, say, where it’s made in a more carbon and energy-intensive way.

So actually while the emissions produced on UK soil go down, the UK’s carbon footprint goes up.

Dieter Helm, the author of a government cost-of-energy review argues we cannot ignore our overall consumption.

“We have to be brutally honest,” he says. “This is one of the reasons why despite everything the people in Europe and the UK have been doing, we haven't made an iota of difference to climate change.”

Helm points out that even a relatively small country such as Denmark, with a population of 5.8 million, has increased its carbon consumption. The increase in the carbon intensity of its imports has far outweighed the reduction in emissions it made through uptake of renewable energy.

Concentration of CO2 in the atmosphere has continued to rise every single year since 1990 despite 30 years of low emissions targets in the West.

“You have to address the incentives which lie in China, India and Africa,” says Helm. “These countries are doubling in size every 10 years in economic input. This is where climate change is going to be determined and we should not have a policy which positively incentivises them to substitute our home production with more carbon intensive output.”

That sounds like a counsel of despair. The UK is responsible for just 1% of global CO2 emissions. Even if we spend a trillion pounds getting our net emissions to zero it won’t make any difference – so why bother?

Baroness Brown says the UK has a moral responsibility to lead, because it has profited so much from emitting CO2 over the years.

“We like to claim that we are the cradle of the industrial revolution. So actually we have a huge responsibility for historic emissions. We should be prepared to make a strong statement now.”

But if, as Baroness Brown points out, we became rich the dirty way, can we really say with any authority that others should do things differently now? Helm says no.

“Preaching to developing countries how they should mend their ways when we've caused much of the problem… is never going to cut it. It's arrogant, it's morally unacceptable and it smacks of imperialism.”

Instead, he suggests that the UK - and the West - should provide the means by which the world’s fastest growing economies can decarbonise.

The biggest of these is China, whose $13tn economy is growing at 6% per year. It’s the world’s biggest burner of coal, but it’s also the biggest global investor in renewables.

Emma Pinchbeck from Renewables UK is optimistic about China’s willingness to adopt low-carbon technology. She thinks that as the country’s “megacities” grow, poor air quality and poor quality of living will create political pressure to tackle the issue.

“The availability of low carbon technology means they may just go straight there. Do not underestimate the visible benefits of low carbon living in the industrial world skipping straight to industrialised economies.”

Panda-shaped solar panels, Datong power plant, China Panda-shaped solar panels, Datong power plant, China

The UK has proved it is possible to grow your economy while reducing emissions. It’s also shown it can lead in green technology adoption.

As well as its leading position in offshore wind, the UK’s particular history and geography means it is well placed to lead in carbon capture and storage (CCS), a process which extracts the carbon from fossil fuels the moment they're burned.

That carbon is then stored securely underground in depleted oil and gas fields. - which by happy coincidence we have right on our doorstep in the North Sea. Many think it is impossible to hit the zero carbon target without developing this technology.

Being in the vanguard of these methods will create industries and expertise the rest of the world will need. It could be a massive export opportunity.

Imagine a world in which renewable power is used to charge a small number of shared electric cars - which double as energy storage units - while also being used to make hydrogen to supplement electric heating systems for well-insulated homes of citizens who eat very little meat and have international travel rationed, with everything managed by optimised networks powered by artificial intelligence (while the humans plant a lot of trees).

It’s a massive environmental, economic, societal and moral journey - and it may be a lonely one.

We need to get moving – down several paths – some of which will turn out to be less successful than others.

It will be very very expensive.

But not as expensive as a climate catastrophe.