Humanity has a dozen years to hold off the accelerated risks of extreme heat waves, wildfires, flooding, drought, sea level rise, and extensive poverty that would result from 2.0°C average global warming by pursuing a tough but doable pathway to 1.5°C, according to a long-awaited science report released in Incheon, South Korea this morning by the Intergovernmental Panel on Climate Change (IPCC).

After months of leaked drafts, warnings that the IPCC was “pulling its punches” to keep the world’s biggest polluters at the table, and intense last-minute efforts to derail the report, the review of about 6,000 scientific studies on key aspects of the climate crisis delivered a stunning set of conclusions, leading to an urgent call to action. It concluded that the Paris Agreement target of 2.0°C average global warming produces impacts far beyond what scientists previously believed, that the 1.5°C “buffer zone” originally added to the Paris deal as a largely aspirational goal is actually the “guardrail” that must not be crossed—and that a target written off as impractical by business-as-usual analysts and interests is actually achievable, albeit with unprecedented action by the world’s governments and citizens.

“Limiting warming to 1.5ºC is possible within the laws of chemistry and physics but doing so would require unprecedented changes,” said IPCC working group co-chair and veteran low-carbon analyst Jim Skea.

“Climate change is occurring earlier and more rapidly than expected. Even at the current level of 1.0°C warming, it is painful,” Hothouse Earth report co-author Johan Rockström told The Guardian. “This report is really important. It has a scientific robustness that shows 1.5°C is not just a political concession. There is a growing recognition that 2.0°C is dangerous.”

“It’s like a deafening, piercing smoke alarm going off in the kitchen. We have to put out the fire,” said UN Environment Programme Executive Director Erik Solheim. “Net zero [emissions] must be the new global mantra.”

“Every extra bit of warming matters, especially since warming of 1.5ºC or higher increases the risk associated with long-lasting or irreversible changes, such as the loss of some ecosystems,” added IPCC working group chair Hans-Otto Pörtner.

“It’s a line in the sand, and what it says to our species is that this is the moment and we must act now,” said working group co-chair Debra Roberts. “This is the largest clarion bell from the science community, and I hope it mobilizes people and dents the mood of complacency.”

“I hope this can change the world,” said report co-author Jiang Kejun of China’s semi-governmental Energy Research Institute. “Two years ago, even I didn’t believe 1.5°C was possible, but when I look at the options I have confidence it can be done. I want to use this report to do something big in China.”

“The document says the world’s annual carbon dioxide emissions, which amount to more than 40 billion tons per year, would have to be on an extremely steep downward path by 2030 to either hold the world entirely below 1.5°C, or allow only a brief ‘overshoot’ in temperatures,” the Washington Post reports. “Overall reductions in emissions in the next decade would probably need to be more than one billion tons per year, larger than the current emissions of all but a few of the very largest emitting countries. By 2050, the report calls for a total or near-total phaseout of the burning of coal.”

On that point, the report points to decarbonization of the electricity sector as one element of the 1.5°C transition that is on track, with the global coal phaseout accelerating, renewable energy costs plummeting, and energy storage now ready for prime time and competing successfully against coal and natural gas on cost.

The Post notes that the IPCC scenarios lean heavily on unproven Biomass with Carbon Capture and Storage (BECCS) systems, “a currently nonexistent program to get power from trees or plants and then bury the resulting carbon dioxide emissions in the ground, leading to a net subtraction of the gas from the air.” BECCS is an unproven and controversial technique described by its harshest critics as science fiction, and a handful of recent studies have shown pathways to 1.5°C without relying on it.

The 91 authors from 40 countries who produced the report “say urgent and unprecedented changes are needed to reach the target, which they say is affordable and feasible although it lies at the most ambitious end of the Paris agreement pledge,” The Guardian reports. With average global warming already at 1.0°C above pre-industrial levels, “the IPCC makes clear that climate change is already happening, upgraded its risk warning from previous reports, and warned that every fraction of additional warming would worsen the impact,” noting that the difference between 1.5 and 2.0°C means:

• 50% fewer people around the world exposed to water stress;
• Hundreds of millions fewer subjected to climate-related poverty, especially in poor countries;
• Food scarcity problems reduced;
• 50% less decline in marine fisheries already suffering from ocean acidification and oxygen loss;
• One-tenth the frequency of ice-free summers in the Arctic;
• 10 million fewer people affected by sea level rise by 2100;
• Nearly 50% less chance that pollinators will lose half of their habitat;
• Considerably better odds that more than 10% of the world’s iconic coral reefs can survive, and subsequently recover.

By contrast, “at 2.0°C, extreme hot days, such as those experienced in the northern hemisphere this summer, would become more severe and common, increasing heat-related deaths and causing more forest fires.”

Despite the dire warnings in the report, Bob Ward of the Grantham Research Institute on Climate Change called the release “incredibly conservative” because it “did not mention the likely rise in climate-driven refugees or the danger of tipping points that could push the world onto an irreversible path of extreme warming,” The Guardian notes.

The IPCC charts four possible pathways to 1.5°C, involving different combinations of land use changes and new technology. “Reforestation is essential to all of them, as are shifts to electric transport systems and greater adoption of carbon capture technology,” The Guardian states. “Carbon pollution would have to be cut by 45% by 2030—compared with a 20% cut under the 2.0°C pathway—and come down to zero by 2050, compared with 2075 for 2.0°C.”

But the ultimate takeaway is that “time and carbon budgets are running out. By mid-century, a shift to the lower goal would require a supercharged rollback of emissions sources that have built up over the past 250 years.”

“We have presented governments with pretty hard choices. We have pointed out the enormous benefits of keeping to 1.5°C, and also the unprecedented shift in energy systems and transport that would be needed to achieve that,” Skea said. “We show it can be done within laws of physics and chemistry. Then the final tick box is political will. We cannot answer that. Only our audience can—and that is the governments that receive it.”

And on that final tickbox, “analysts say there is much work to be done, with even pro-Paris deal nations involved in fossil fuel extraction that runs against the spirit of their commitments,” The Guardian notes. “Britain is pushing ahead with gas fracking, Norway with oil exploration in the Arctic, and the German government wants to tear down Hambach forest to dig for coal.”

(And Canada has just bought itself an aging tar sands/oil sands pipeline and is celebrating the announcement of a new $40-billion liquefied natural gas terminal. Because “Canada is back, my friends. Canada is back, and we’re here to help.—Ed.)

“At the current level of commitments, the world is on course for a disastrous 3.0°C of warming,” The Guardian states. “The report authors are refusing to accept defeat, believing the increasingly visible damage caused by climate change will shift opinion their way.”