The United Nations is poised to release a major new capstone report to provide a sobering reminder that time is running out if humanity wants to avoid passing a dangerous global warming threshold. More than a decade ago that threshold was agreed, and we were warned not to pass.
In the realm of climate diplomacy, it's the little engine that could, the 80-to-1-odds Kentucky Derby winner, the low-budget multiverse fantasy that came out of nowhere to sweep the Oscars. We are talking, of course, about the Paris Agreement goal of capping Earth's average surface temperature at 1.5 degrees Celsius (2.7 degrees Fahrenheit) above levels in the late 19th century, when burning fossil fuels began to seriously heat up the planet.
At barely 1.2 degrees Celsius above that threshold, the world today has already seen a crescendo of deadly and destructive extreme weather.
Fifteen years ago, a 1.5 degrees Celsius limit on global warming – championed by small island nations worried about sea level rise – was rejected by most scientists as unrealistic and by most countries as unnecessary.
A 2 degrees Celsius "guardrail" was assumed to be safe enough.
Today, the 1.5 degrees Celsius target is enshrined in everything, everywhere, all at once. While technically no more than an "aspirational" goal, it has become the de facto North Star for United Nations climate talks, national climate plans and the business world.
From Apple and Facebook to Big Pharma and even Big Oil, multinationals have unveiled promises and plans to be "1.5 Celsius-aligned," even if most of those plans don't hold up very well under scrutiny.
You can draw a straight line from 1.5 degrees Celsius to the science-base imperative to nearly halve global emissions by 2030 and achieve net zero around mid-century, meaning any residual carbon pollution must be offset by removals.
Both of these targets are set to be affirmed in a report summarizing six years of climate science, released Monday by the U.N.'s Intergovernmental Panel on Climate Change (IPCC).
This raises a perplexing question, according to Beatrice Cointe, a sociologist at France's National Center for Scientific Research and co-author of a recent study on the history of the 1.5 degrees Celsius target.
"How did an almost impossible target become the point of reference for climate action?" she asked.
And what will happen when the world experiences its first full year at or above 1.5 degrees Celsius, which the IPCC says could easily happen within a decade, even under aggressive emissions reduction scenarios?
"The target appears increasingly unattainable," Cointe and co-author Helene Guillemot, a historian of science at the Centre Alexandre-Koyre, wrote in the journal WIREs Climate Change.
"And yet calls to 'Keep 1.5 Celsius Alive' have been growing louder."
The backstory of the 1.5 degrees Celsius goal reveals an interplay of science and politics, with one driving and shaping the other.
Going into the 2015 climate negotiations that yielded the breakthrough Paris treaty, it seemed unlikely that 195 nations would significantly improve on the 2 degrees Celsius target already set in stone.
But a scientific evaluation by a U.N. technical body delivered ahead of the December summit sounded an alarm about the dangers of a +2 degrees Celsius world and suggested greater ambition might be wise.
"While the science on the 1.5 Celsius limit is less robust, efforts should be made to push the defensive line as low as possible," it concluded.
A growing coalition of developing nations, meanwhile, had gathered behind the 1.5 degrees Celsius goal, eventually joined by the European Union and the United States.
Emerging giants and oil exporters baulked, fearful of the constraints on their fossil-fuel-dependent economies.
"China was against it, India was against it, Saudi Arabia fought us tooth-and-nail to the very end," recalled Saleemul Huq, director of the International Center for Climate Change and Development in Dhaka.
Even today, these nations remain lukewarm on the idea.
But in the end, nearly 200 nations committed to cap warming at "well below 2 Celsius," while "pursuing an effort to limit the temperature increase to 1.5 Celsius."
It was a stunning diplomatic coup. Many scientists, however, were less than thrilled.
"It will be very hard – if not impossible – to keep warming below 1.5 degrees Celsius during the entire 21st century," Joeri Rogelj, a climate modeler currently at Imperial College London who played a key role in the technical report, told Agence France-Presse (AFP) at the time.
But because the target was part of the Paris Agreement, nations called on the IPCC – which exists to brief policymakers on climate science – for a "special report."
The resulting bombshell, delivered in October 2018, left no doubt as to the difference a half-a-degree makes: a 1.5 degrees Celsius world will see deep change but remain liveable; a 2 degrees Celsius world could tip the climate system into overdrive, outstripping our capacity to adapt, it warned.
Today, the IPCC – including Rogelj, a lead author of the 2018 report – insists that the 1.5 degrees Celsius goal is technically feasible.
But that conclusion hangs by the thinnest of threads.
There is no scenario that avoids "overshooting" the target, and bringing temperatures back under the wire will require extracting billions of tons of CO2 from thin air, something we can't do yet at scale.
However, whether the 1.5 degrees Celsius target is feasible may be missing the point, say others.
"Getting 1.5 Celsius into the agreement was a moral target," Huq told AFP not long after the Paris pact was inked.
"It's our leverage, the whip we will use to hit everybody on the back so they can go faster," he added.
"Whether we achieve it or not is going down a dark track. From now on, it's about raising ambition."
Piers Forster, director of the University of Leeds Priestley International Center for Climate and a coordinating lead author for the IPCC, describes the 1.5 degrees Celsius objective as a "huge, but not impossible, task."
"Hopefully, the IPCC report can push the urgency," he told AFP. "If it's ignored, we would have to give up on 1.5 Celsius."
