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The UK's official advisers have issued a sombre assessment of government plans to hold climate change at a safe level.

The Committee on Climate Change (CCC) says the government is not on track to meet its pledge of cutting emissions 80% by 2050.

And they controversially warn ministers to park their recent ambition to tighten carbon reduction targets to protect vulnerable nations.

Ministers say they are determined to tackle climate change.

They say they will publish new policies soon.

They support the Paris Agreement on climate which commits to holding temperature rise to 2C - preferably 1.5C.

But the committee is warning the government not to run before it has proved that it can walk.

They controversially advise ministers not to adopt stricter targets for the moment, even though poor nations say they are essential.

Mind the gap

The report states: "Do not set new UK emissions targets now. The UK already has stretching targets to reduce greenhouse gas emissions.

"The priority for now should be robust near-term action to close the gap to existing targets and open up options to reach net zero emissions.

"The most important contribution the government can make now to the Paris Agreement is publishing a robust plan to meet the UK carbon budgets and delivering policies in line with the plan."

It says the government can re-visit the 1.5C ambition in the future.

The advice has infuriated campaigners. Craig Bennett from Friends of the Earth told BBC News: "The job of the committee is to offer advice on carbon budgets based on the scientific evidence, not what feels politically expedient.

"What message will it send to the world for Britain, once a climate leader, to give up on one central tenets of the Paris Agreement less than 12 months after it was signed?

"It's no surprise that the government's approach to climate policy is failing. A five-year-old could tell you building runways, allowing new open-cast coal mines, and forcing fracking on local communities while doing precious little to support renewables or energy saving isn't going to help us limit temperature rises to 1.5 degrees.

"But it's government policy that needs to change and fast, not the targets."

The committee is important because it provides step-by-step technical guidance for government to meet targets stipulated under the Climate Change Act.

Capturing carbon

The first phase of the planned low-carbon transformation - making electricity almost entirely low-carbon by the early 2030s - is more or less on track, members say.

But the government is lagging badly in preparations for the next phase, electric vehicles. And most disturbingly, plans for heating the UK's homes - the last phase - are in disarray as the heat pump technology thought likely to keep us warm in coming decades has failed to meet expectations.

The committee now wants the government to prepare for natural gas in homes to be supplanted by hydrogen, which would entail a revamp of the gas grid and replacement of existing boilers and cookers over time in a process similar to the switch from town gas to natural gas in the 1960s.

But, it says, this will only work if carbon capture technology is used when the hydrogen is produced, and the carbon emissions buried into rocks. This technology has been touted as the get-out-of-jail option for years - but plans to develop it have stalled, mostly because of the cost.

The report warns: "Current decarbonisation policies, at best, will deliver about half the required reduction in emissions. Acting with urgency to close this policy gap would reduce long-term costs and keep open options for the future."

The government admits its low carbon strategy is lagging but the climate minister Nick Hurd previously told me the issue was complex, and it was better to deliberate a while than to adopt the wrong policies.

The strategy is supposed to be out before Christmas but he said it could be delayed until next year.

CO2 measures

If the government adopts a new target of 1.5C the committee says that would entail reducing emissions to what's known as net zero - in which any emissions are offset by activities that soak up CO2.

The committee warn that even with full deployment of known low-carbon measures some UK emissions will remain, especially from aviation, agriculture and parts of industry.

That will mean taking CO2 out of the atmosphere to compensate by various measures, including: planting forests to absorb carbon dioxide; investing in materials that store carbon; burning wood for energy and capturing the emissions; using timber for buildings; encouraging the weathering of rocks, which buffers CO2 - and ultimately directly sucking in CO2 from the atmosphere.

The report says the government should prepare for these technologies to be ready by 2050 to be deployed at scale. It says: "We agree with the government's intention to set a new target in future that reflects the global need to reach net zero emissions.

"However, to be credible it needs to be evidence-based, accompanied by strong policies to deliver existing targets and a strategy to develop greenhouse gas removals."

'Valuable advice'

This reflects sentiment at a recent Oxford conference on removing CO2 emissions. Academics who had previously viewed CO2 removal as a sign of government policy failure were increasingly willing to support the technologies as an unfortunate necessity for keeping the earth habitable.

Even with the CO2 capture technology, difficult choices will have to be made, the report says: "Reducing residual sources of emissions to close to 100 MtCO2e (million metric tonnes of CO2 equivalent) per year would require stretching options in hard-to-treat sectors, such as substantial biofuel use in aircraft and reduced red meat consumption in diets."

A committee spokeswoman rejected the criticism from Friends of the Earth. She said: "The CCC is very clear that the priority now is for Government action.

"The CCC welcomes the Paris Agreement. More work needs to be done on how to translate the net zero goal into a feasible, credible long-term target for the UK."

The government has committed to cutting emissions but the prime minister says her priorities are energy cost and energy security.

A spokesman for the Department for Business, Energy and Industrial Strategy said it would "carefully consider the valuable advice" from the CCC.

He added: "We are already making good progress towards meeting our goal of reducing emissions by at least 80% by 2050 on 1990 levels, and we are now looking ahead to set out how we will continue to decarbonise through the 2020s."

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