The UN's 195-nation climate science body plunged deep into overtime Saturday to finalise a report outlining stark options -- all requiring a global makeover of unprecedented scale -- for avoiding climate chaos.

Working through the night, the closed-door huddle in rain-soaked Incheon, South Korea, was to convene a plenary later in the day to hammer through a "Summary for Policymakers."

Can humanity cap global warming at 1.5 degrees Celsius (2.7 degrees Fahrenheit)? What will it take and how much will it cost? Would climate impacts be significantly less severe than in a 2C world?

The Intergovernmental Panel on Climate Change (IPCC) was tasked with these questions by the framers of the landmark 2015 Paris Agreement, which calls for halting the rise in temperatures to "well below" 2C -- and 1.5C if possible.

That aspirational goal -- tacked on to the treaty at the last minute -- caught climate scientists off-guard.

"Our understanding of 1.5C was very limited, all but two or three of the models we had then were based on a 2C target," said Henri Waisman, a senior researcher at the Institute for Sustainable Development and International Relations in Paris, and one of the report's 86 authors.

Based on more than 6,000 peer-reviewed studies, the 20-page bombshell will make for grim reading when it is released on Monday.

"Leaders will have nowhere to hide once this report comes out," said Jennifer Morgan, Executive Director of Greenpeace International, and an observer at the talks.

- 'Negative emissions' -

At current rates of greenhouse gas emissions, Earth will zoom past the 1.5C signpost around 2040, and as early as 2030.

After only one degree of warming, the world has seen deadly storms engorged by rising seas and a crescendo of heatwaves, drought, flooding and wild fires made more intense by climate change.

Without a radical course change, we are headed for an unliveable 3C or 4C hike.

And yet, humanity has avoided action for so long that any pathway to a climate-safe world involves wrenching economic and social change "unprecedented in terms of scale," the report said.

"Some people say the 1.5C target is impossible," said Stephen Cornelius, WWF-UK's chief adviser for climate change, and a former IPCC negotiator.

"But the difference between possible and impossible is political leadership."

The report is set to lay out four scenarios that could result in Earth's average surface temperature stabilising at 1.5C.

The most ambitious -- dubbed the "low energy scenario" -- would see a radical drawdown in energy consumption coupled with a rapid shift away from fossil fuels and a swift decline in CO2 emissions starting in 2020.

It would not require a temporary "overshoot" of the 1.5C threshold, and does not depend on sucking vast quantities of CO2 out of the air, known as carbon dioxide removal, or "negative emissions."

A second pathway emphasises the need for changing our consumption patterns -- eating less meat, travelling less, giving up cars, etc. -- along with an overhaul of agricultural and land-use practices, including the protection of forests.

- Running interference -

The final scenario compensates for a "business-as-usual" economy and lifestyle by allowing a large overshoot of the 1.5C target.

It also calls for burning a lot of biofuels and capturing the emitted CO2, a system known by its acronym, BECCS. Indeed, an area twice the size of India would have to be planted in biofuel crops.

This "P4" plan also assumes that some 1200 billion tonnes of CO2 -- 30 years' worth of emissions at current rate -- will be socked away underground.

Signficantly, and for the first time, the UN panel quantified changes in the use of coal, oil and gas.

For the low-energy demand pathway, for example, coal consumption would drop 78 percent by 2030, and 97 percent by mid-century. Oil would decline by 37 and 74 percent, respectively, and gas by 25 and 74 percent.

The pathway of least resistance, by contrast, would still see nearly a doubling of oil use by 2030, and a 37 jump in gas.

Coal is a big loser in all the scenarios.

The US delegation -- the first since Donald Trump took office to work on an IPCC report -- did not throw a monkey wrench into the process, as many here had feared.

"The United States is quite constructive, though I don't think they want that said out loud," said on delegate who asked not to be named.

Besides special reports, the IPCC has issued five major Assessment Reports that serve as the scientific foundation for UN climate talk. The next one is due in 2022.

Key points in the UN report on climate change
Incheon, South Korea (AFP) Oct 8, 2018 - The landmark UN report on limiting global warming to 1.5 degrees Celsius was released in South Korea on Monday after a week-long meeting of the 195-nation Intergovernmental Panel on Climate Change (IPCC).

A "Summary for Policymakers" of the 400-page tome underscores how quickly global warming has outstripped humanity's attempts to tame it, and outlines stark options -- all requiring a makeover of the world economy -- for avoiding the worst ravages of climate change.

Here are key findings, grounded in some 6,000 peer-reviewed scientific studies:

- 'Unprecedented changes' -

Capping global warming at 1.5C (2.7 degrees Fahrenheit) above pre-industrial levels will require "rapid, far-reaching and unprecedented changes in all aspects of society", the IPCC said.

Earth's average surface temperature has already gone up 1C -- enough to unleash a crescendo of deadly extreme weather -- and is on track to rise another two or three degrees absent a sharp and sustained reduction in carbon pollution.

At current levels of greenhouse gas emissions, we could pass the 1.5C marker as early as 2030, and no later than mid-century, the report finds with "high confidence".

To have at least a 50-50 chance of staying under 1.5C without overshooting the mark, the world must, by 2050, become "carbon neutral".

Emissions of carbon dioxide -- the main greenhouse gas -- should peak no later than 2020 and curve sharply downward from there, according to scenarios in the report.

Easier said than done: humanity dumped a record amount of CO2 into the atmosphere last year.

- The steep cost of inaction -

The 30-page executive summary also details humanity's "carbon budget" -- the amount of CO2 we can emit and still stay under the 1.5C ceiling.

For a two-thirds chance of success, that is about 420 billion tonnes, an allowance that would -- according to current trends -- be used up in a decade.

The share of electricity generated by renewables -- mainly hydro, solar and wind -- would have to jump by mid-century from about 20 to 70 percent. The share of coal, meanwhile, would need to drop from 40 percent to low single digits.

Limiting global warming to 1.5C will require investing about $2.4 trillion (2.1 trillion euros) in the global energy system every year between 2016 and 2035, or about 2.5 percent of world GDP.

This price tag, however, must be weighed against the even steeper cost of inaction, the report says.

- 1.5C vs. 2C -

Two degrees Celsius was long considered the temperature guardrail for a climate-safe world, but a raft of recent research shows otherwise.

"Climate impacts are exponentially more dramatic when we go from 1.5C to 2C," said Henri Waisman, a scientist at the Institute for Sustainable Development and International Relations, and a coordinating lead author of the IPCC report.

What used to be once-a-century heatwaves in the northern hemisphere, for example, will become 50 percent more likely in many regions with an extra half-degree of warming.

Some tropical fisheries are likely to collapse somewhere between the 1.5C and 2C benchmark. Staple food crops will decline in yield and nutritional value by an extra 10 to 15 percent. Coral reefs will mostly perish. The rate of species loss will accelerate "substantially".

Most worrying of all, perhaps, are temperature thresholds between 1.5C and 2C that could push Arctic sea ice, methane-laden permafrost, and melting polar ice sheets with enough frozen water to lift oceans by a dozen metres, past a point of no return.

- Pathways -

IPCC authors say the 1.5C goal is technically and economically feasible, but depends on political leadership to become reality.

The report lays out four 1.5C scenarios that shadow current and future policy debates on the best way to ramp up the fight against climate change.

One pathway, for example, relies heavily on a deep reduction in energy demand, while another assumes major changes in consumption habits, such as eating less meat and abandoning cars with internal combustion engines.

Two others depend on sucking massive amounts of CO2 out of the air, either though large-scale reforestation, use of biofuels, or direct carbon capture.

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UN report on global warming target puts governments on the spot
Paris (AFP) Oct 1, 2018
Diplomats gathering in South Korea Monday find themselves in the awkward position of vetting and validating a major UN scientific report that underscores the failure of their governments to take stronger action on climate. "This will be one of the most important meetings in IPCC history," Hoesung Lee, chair of the UN's Intergovernmental Panel on Climate Change, told delegates at the opening plenary in Incheon. The special report on global warming of 1.5 degrees Celsius (2.7 degrees Fahrenheit) ... read more