'Now or never': UN urges action to avoid climate catastrophe

Temperatures on Earth will shoot past a key danger point unless greenhouse gas emissions fall faster than countries have committed, the world’s top body of climate scientists has said, warning of the consequences of inaction but also noting hopeful signs of progress.

The 2,800-page report by the UN's Intergovernmental Panel on Climate Change (IPCC) documents to "a litany of broken climate promises", said UN chief Antonio Guterres on Monday in a blistering judgment of governments and industry.

“It is a file of shame, cataloguing the empty pledges that put us firmly on track towards an unlivable world,” he said.

IPCC chief Hoesung Lee said that "we were at a crossroads". "The decisions we make now can secure a liveable future."

There are solutions, the report says, but they touch on virtually all aspects of modern life and require significant investment and need "immediate action". 

"It's now or never, if we want to limit global warming to 1.5C," said Jim Skea, a professor at Imperial College London and co-chair of the working group behind the report. 

READ MORE: World 'sleepwalking' to climate catastrophe: UN

Not without hope

The very first item on the global to-do list is to stop greenhouse gas emissions from rising any further, the report said.

That must be done before 2025 to have a hope of keeping within even the less ambitious warming targets of the Paris deal of two degrees Celsius above preindustrial levels. Scenarios of catastrophic 2.5C of warming also have emissions peaking within three years.

Beyond that, the report said carbon emissions need to drop 43 percent by 2030 and 84 percent by mid-century to meet the more ambitious Paris goal of 1.5C.

"Without immediate and deep emissions reductions across all sectors, it will be impossible", Skea said.

Governments agreed in the 2015 Paris accord to keep global warming well below 2C this century, ideally no more than 1.5C. Yet temperatures have already increased by over 1.1C since pre-industrial times, resulting in measurable increases in disasters such flash floods, prolonged droughts, more intense hurricanes.

The IPCC report is not without some hope, however. Its authors highlight myriad ways in which the world can be brought back on track to 2C or even, with great effort, return to 1.5C after that threshold has been passed. 

This could require measures such as the removal of CO2 from the atmosphere with natural or artificial means, but also potentially risky technologies such as pumping aerosols into the sky to reflect sunlight.

Among the solutions recommended are a rapid shift away from fossil fuels toward renewable energy such as solar and wind, the electrification of transport, more efficient use of resources and massive financial support for poor countries unable to pay for such measures without help.

READ MORE: The small window to act on climate change is closing – IPCC