In a controversial move, the United Nations chief is today calling on polluting developed countries like the UK to “fast forward” net zero targets by a decade to 2040, warning the “climate time bomb is ticking”.

It comes as the most comprehensive review yet of the state of climate change delivers a bleak picture of humanity’s failure to tackle it, warning the window to secure a “liveable and sustainable future” is “rapidly closing”.

But climate scientists have rallied to point out there are still grounds for hope.

Today’s report from the United Nations’ IPCC is the culmination of eight years of work by hundreds of the world’s leading climate scientists, summarising six underlying reports.

The final sign-off by all governments was repeatedly pushed back amid a battle between rich and developing countries over emissions targets and financial aid to vulnerable nations.

The last similar report in 2014 paved the way for the ambitious Paris Agreement the following year.

The next of its kind won’t arrive until 2030, making this effectively the last collective warning and action plan from scientists while the 1.5°C warming is still in reach – though only just.

Key findings of the IPCC report

• Human activity has “unequivocally” warmed the planet by 1.1°C above pre-industrial levels.
• Emissions must fall 48% by 2030 – the first time such a bold target has been signed off in a global political document.
• Climate risks make things like pandemics or conflicts worse.
• Emissions from existing fossil fuel infrastructure alone would blow the agreed 1.5°C warming target, unless they are captured via still risky technology.
• Global sea levels have already risen by 20cm on average.
• At least 3.3 billion people are “highly vulnerable” to impacts including “acute food insecurity” and water stress.
• Extreme heat is already killing people in every region.
• Vulnerable communities who have historically contributed the least are disproportionately affected.

‘Hope not despair’

In the year since the last report in this series, the world has suffered violent flooding in Pakistan, drought across the northern hemisphere and a hunger crisis in the Horn of Africa – all of which were made worse by climate change.

But amid the bleak warnings of lost jobs, homes, crops and lives, scientists insisted there were still grounds for hope.

IPCC chair Professor Hoesung Lee painted a picture of a “liveable sustainable future for all” – though only if we “act now.”

“We should feel considerable anxiety,” said Professor Emily Shuckburgh from Cambridge University, who recently co-authored a book on climate change with King Charles, but was not involved with this report.

“But hope, rather than despair,” she added, highlighting that the IPCC said it’s still possible to limit warming to the agreed safer threshold of 1.5°C.

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The report says changes in how we eat, travel, heat our homes and use the land can all cut climate-heating gases, while reducing air pollution, improving health and boosting jobs.

And there is enough global capital to rapidly slash climate-heating pollution.

“Not despair, but not just hope, because there is a lot of work to do,” said Dr Friederike Otto, a member of the core writing team and senior lecturer at Imperial College London.

“But we don’t need any new magic invention that we have to do research on for the next 30 years or so. We have the knowledge… But we also need to implement this.”

‘The wolf is at the door’

But because the window to act is “rapidly closing,” the UN Secretary-General Antonio Guterres will today attempt to heap pressure on rich nations to make up for lost time.

In 2018 the IPCC loudly warned of the “unprecedented scale of the challenge required to keep warming to 1.5°C”.

Five years later, that challenge is “even greater” due to a failure to cut emissions enough, it said.

“Leaders of developed countries must commit to reaching net zero as close as possible to 2040,” Mr Guterres is expected to say shortly.

“This can be done,” he will add in an address to launch the report, which he calls “a how-to guide to defuse the climate time bomb”.

Mohamed Adow, director of thinktank Power Shift Africa, said it was “only fair that Guterres is setting more ambitious goals for wealthier countries who can make the transition more quickly and who have got rich off the back of burning fossil fuels”.

But the proposal may spark some backlash for apparently moving the goalposts. Countries are already struggling to meet the previously agreed target of net zero by 2050.

Asked about the proposed date change, a UK government spokesperson said: “Today’s report makes clear that nations around the world must work towards far more ambitious climate commitments.”

Britain is currently off track to get its emissions to net zero even by 2050, according to an independent assessment last week, and the recent budget was criticised for falling short on climate policies.

Rebecca Newsom, head of politics at Greenpeace UK, said: “Forget distant tropical islands and future generations – we have already seen what 40°C summers and flash flooding look like here in the UK. The wolf is at the door.”

Fossil fuel battleground at COP28

The COP28 climate summit will take place in the United Arab Emirates in December.

The findings of the latest IPCC report are supposed to inform those climate negotiations in Dubai.

This year’s summit is seen as particularly important, taking a “global stocktake” of how countries have progressed since the 2015 Paris Agreement.

Observers pointed out that every government had signed off on the scientific conclusions released today, which include the call for a “substantial reduction in fossil fuel use”.

The necessary approval process by all nations is designed to ensure governments act on the contents.

Yet some countries resist that language in other forums such as the more political COP climate summits, with oil and gas states last year blocking a pledge to “phase down all fossil fuels” from the final agreement at COP27 in Egypt.

“By signing off the IPCC reports all governments, even those of high-emitting countries such as Saudi Arabia, Australia, the US and the UAE, acknowledge that climate change is a real and present danger,” said Richard Black from energy thinktank ECIU.

The UN will hope there is similar agreement in December – which needs to result in meaningful action.

Watch the Daily Climate Show at 3.30pm Monday to Friday, and The Climate Show with Tom Heap on Saturday and Sunday at 3.30pm and 7.30pm.

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The show investigates how global warming is changing our landscape and highlights solutions to the crisis.