Governments of 175 nations marked Earth Day at the United Nations on Friday by signing the landmark Paris Agreement on the climate crisis. This sets in motion an unexpectedly swift process that the treaty's supporters hope will hasten its coming into force well before its target date in 2020.
Their urgency stems from danger signs that the planet is headed rapidly toward unusually high climate risks. Never in the record books has the world's temperature risen so high, nor the blanket of carbon dioxide causing the warming been so thick.
Still, treaty advocates struck mainly positive notes, citing a "Paris effect" that optimists say is driving government policies, energy choices, and investments in a new, low-carbon direction. For example, for the first time, growth of the world's economies seems to have been decoupled from growth in emissions of carbon dioxide, the main greenhouse gas.
But everyone recognizes, as they did in December when the accord was signed in Paris, that the pledges are far short of what is needed.
That's one reason why some of the biggest carbon polluters as well as some of the most vulnerable states are prodding as many nations as possible not just to sign today, but to quickly take the next steps to ratify it quickly so it can enter into force.
Secretary of State John Kerry, who has spent a long political career working toward this day and signed the document with his granddaughter in his arms, said the United States would formalize its adherence this year. (The treaty is structured such that it does not require a Senate vote.)
The question is whether the U.S. has the political will to increase its ambitions in the next couple of years; one often-cited analysis, by the Rhodium Group, says that the current goals are "within reach," if admittedly inadequate.
China is moving fast, too, promising to ratify before a meeting of the G-20 industrial nations in September, and urging others to do likewise—but its goals are less ambitious. And the European Union, long a very ambitious bloc, has become bogged down in internal politics. Still, there seems little doubt that that the requisite 55 nations accounting for 55 percent of all pollution will move forward in short order, probably locking the treaty into place sometime in the next year or two.
That's especially important if the treaty's goals are ever to be met—far from a sure thing, and possible only if most of the world achieves more than promised so far, and faster than previously suggested.
In Paris, 195 nations agreed to carry out national promises bending their emissions downward as fast as possible, aiming to keep the planet's ultimate warming to at most 2 degrees Celsius, and hopefully as low as 1.5 degrees. That would require rapidly eliminating the use of fossil fuels (or installing carbon-capture technology) to reach no net growth of greenhouse gases in the second half of this century.
This month, UN negotiators in Nairobi told a special science panel to quickly nail down the evidence for the lower temperature target.
Already, the scientific literature is pointing clearly toward the need for more ambition.
One new paper, published in Earth Systems Dynamics and presented to the European Geosciences Union, found that "tropical regions—mostly developing countries that are already highly vulnerable to climate change—face the biggest rise in impacts between 1.5°C and 2°C," said one author, William Hare, a senior scientist and chief executive of Climate Analytics.
Co-author Jacob Schewe, of the Potsdam Institute for Climate Impact Research in Germany, said: "Some researchers have argued that there is little difference in climate change impacts between 1.5°C and 2°C." But taking into account natural variabilities and model uncertainties, "at the regional level, we clearly show that there are significant differences in impacts between 1.5°C and 2°C."
According to a breakdown by ClimateInteractive, here's how major players would have to increase the ambition of their pledges to move from the status quo to 2 degrees or 1.5 degrees:
Europe, which has pledged to get 40 percent below 1990 levels by 2030, would have to go to 47 percent for 2 degrees, and 62 below for 1.5 degrees. The United States, which has pledged to get at least 26 percent below 2005 levels by 2025 for 2 degrees, would have to reach 60 percent to achieve 1.5 degrees. These numbers are similar to other developed countries.
China, instead of peaking emissions by 2030 at 60 percent of the carbon intensity of 2005, would have to peak by 2025 to meet either goal. Other developing countries would face nearly as short timelines for reaching peak emissions.
But rather than moving toward either of these two targets – 2 degrees or 1.5 – the world right now is falling well short, as measured by the sum of all the individual pledges filed by all the countries – the nationally determined contributions, or NDCs, as they are known.
"The emissions gap is set to grow," said a recent report by two analysts at Chatham House, of the Royal Institute of International Affairs. "While a 2-degree C pathway requires a rapid decline in annual global net emissions to close to zero by the end of the century, the NDC's imply that emissions will continue to rise throughout that period."
"The next five years are crucial," it said. Unless ambitions are increased swiftly, the growing emissions gap would grow too fast. That would make what looks extremely difficult now a self-fulfilling impossibility.