̽»¨¾«Ñ¡

This is an excerpt of a piece that originally ran on .

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 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 so high, nor the causing the warming been so thick.

Still, treaty advocates struck , 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 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 not just to sign today, but to quickly 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, . (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 , 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 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 .

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.

You can read the rest of , and learn more about what the Paris Agreement means for birds and the planet.

 is a Pulitzer prize-winning, nonprofit, non-partisan news organization that covers clean energy, carbon energy, nuclear energy and environmental science—plus the territory in between where law, policy and public opinion are shaped. Its mission is to produce clear, objective stories that give the public and decision-makers the information they need to navigate the heat and emotion of climate and energy debates.