Paris, Jan 18: When future generations write the history of humanity's faltering quest to repair Earth's climate system, 2015 will have its own chapter.
Nature, along with the usually fractious family of nations, conspired to make it a landmark year: almost certainly the hottest on record for the planet as a whole, and a rare moment of unity when 195 states pledged to curb the carbon pollution that drives global warming.
Whether the December 12 Paris Agreement is the key to our salvation or too-little-too-late depends on what happens starting now, experts and activists told AFP.
"The most compelling thing you can say about Paris is not that it saved the planet, but that it saved the chance of saving the planet," said Bill McKibben, founder of the grassroots organisation 350.org and an architect of the worldwide movement to divest from fossil fuel companies.
Robert Stavins, director of the Harvard Environmental Economics Program at the Harvard Kennedy School, was also chary: "We will only be able to judge whether it is truly a success years, perhaps decades, from now."
But whatever lies ahead, they all agree, the last year has been a "tipping point" on climate change. "Paris represented a real sea change in seriousness in coming to grips with the issue," said Alden Meyer, a veteran climate analyst from the Washington-based Union of Concerned Scientists who has followed the UN process for nearly three decades.
Much of that seriousness was driven by a crescendo of deadly extreme weather and the growing confidence of science in connecting the dots with long-term shifts in climate.
The US National Oceanic and Atmospheric Administration will likely report Wednesday on record-breaking heat in 2015.
They could point to the most powerful hurricane ever registered; freakish, above-freezing temperatures -- if only for a day -- at the North Pole in December; or life-threatening droughts in eastern and southern Africa.
Some of that will be chalked up to El Nino, a natural weather pattern that creates havoc along the tropical and southern Pacific Rim every five or six years.
But the very fact that this El Nino is the most intense ever measured may itself be a by-product of global warming.
Scientists reported last week that climate change has probably pushed back the next Ice Age by 50,000 years.
That may sound like good news, but more than anything it is a stunning testament to the extent to which human activity -- mainly burning fossil fuels -- has played havoc with the planet's thermostat.
Experts have also come a step closer to concluding that our impact on Earth's bio-chemical systems has been so massive as to justify the christening of a new geological era.