United Nations (UN) Secretary-General Antonio Guterres cautioned rich nations against the “climate time bomb, which he said, is ticking” and urged stakeholders to work on an urgent basis to curb emissions sooner after a new assessment from scientists said there was little time to lose in tackling climate change.

Guterres raised an alarm pointing towards the rate of temperature rise in the last half-century, which is the highest in 2,000 years.

“Concentrations of carbon dioxide are at their highest in at least 2 million years. The climate time bomb is ticking," he said.

According to him, the sixth “synthesis report” from the UN’s Intergovernmental Panel on Climate Change (IPCC) is “a survival guide for humanity”.

He appealed to developed countries to commit to reaching net zero emissions by the earlier date of around 2040.

The synthesis report, which is designed to provide clarity for policymakers as they consider further action to slash emissions, contains the summarised findings from three expert assessments published between 2021 and 2022 that looked at the physical science, impacts, and mitigation of climate change. 

“We have the tools to stave off and reduce the risks of the worst impacts of the climate crisis, but we must take advantage of this moment to act now,” said US climate envoy John Kerry.

The 37-page report serves as a guide for a global climate change “stocktake” set to take place this year, in which countries will assess progress. Under the 2015 Paris Agreement, nations are also expected to update climate pledges by 2025.

According to the IPCC, emissions must be halved by the mid-2030s if the world is to have any chance of limiting temperature rise to 1.5 degrees Celsius (deg C) (2.7 Fahrenheit) above pre-industrial levels – a key target enshrined in the Paris accord.

“If we act now, we can still secure a liveable sustainable future for all,” said IPCC chair Hoesung Lee.

Environmentalists often raise alarm over the fact that the planet is on track to warm by 3.2 degrees Celsius by the century’s end, and temperatures could still rise by at least 2.2 degrees Celsius even if existing pledges are met.

Average temperatures are already 1.1 deg C higher than 1850-1900 levels, driving more extreme weather events worldwide. “In the words of very senior colleagues in the IPCC, we’re up the proverbial creek – that’s really the key message from the report,” said synthesis report co-author Frank Jotzo of Australian National University.

Observers said the major areas of contention included the language around finance and the projected impacts of climate change, as well as the issue of “equity” and climate justice for poorer countries.

Some governments also wanted to give more prominence to their favoured climate solutions, including solar power or carbon capture.

Amid dangers of more extreme weather, rapidly rising sea levels, melting Arctic ice, and the growing likelihood of catastrophic and irreversible “tipping points”,  the IPCC advocated that the world needs to accelerate the transition to green energy and transform agriculture and eating habits if it has any chance of making the necessary cuts in emissions.

Experts expressed concern because nearly half the world’s population was already vulnerable to climate impacts.