All around the world, national governments are trying to hammer out their global warming policies, preparing for the United Nations' climate-change conclave in Copenhagen, Denmark, at the end of 2009. And in too many places, the effort seems to be going nowhere.

Here in Australia, for instance, the government weakened major elements of its "emissions trading scheme," bowing to pressure from the coal industry, which is the country's biggest exporter, and other major polluters.

In Washington, meanwhile, the Obama administration is valiantly helping to push a bill through Congress that would finally set a cap on U.S. carbon emissions. If the leaks coming out of Capitol Hill are correct, it's watered down with lots of compromises. These concessions are clearly necessary to win passage, but they may also limit the speed and breadth of the legislation's effect.

The trouble is, physics and chemistry aren't adjusting their schedule to fit our political and economic convenience. Each week brings new accounts of crashing ice sheets and spreading droughts. The journal Nature said in its April 29 edition that a growing number of scientists agree the carbon dioxide challenge "is even greater than had been previously thought."

The problem isn't feckless public officials or lack of effort. The environmental movement simply isn't big enough. It's nowhere near big enough to take on the fossil fuel industry, the biggest player in our global economy. It's like sending the Food and Drug Administration to fight the war in Afghanistan.

Exxon Mobil Corp. made more money in 2008 than any U.S. company in the history of money. It has more clout than all the green groups combined. Which is why, if the Copenhagen conference is going to be anything but a disaster, we need to build a stronger movement. All around the world. Very fast.

That sounds quixotic, but maybe not. I'm here in Australia, organizing people for a new campaign called 350.org. We take our name from the most important number in the world, a number that scientists only identified about 18 months ago. It's the amount of carbon dioxide, measured in parts per million in the atmosphere, that scientists now say is the safe maximum for the planet — a maximum we're well past. Currently, our atmosphere holds 387 parts per million, which is precisely why the Arctic is melting, precisely why Australia is catching on fire.

Our plan is simple. We asked people around the world, through our Web site, to hold organized actions on Oct. 24 — from high in the Himalayas to underwater on the Great Barrier Reef, from Easter Island to inner-city America — in an effort to take that number and drive it into the human imagination.

Already, more than 700 actions have been planned in a third of the world's countries. There will be 350 bicyclists leaving on 350-kilometer trips, and 350 surfers on waves in one beach town after another; 350 divers at the Great Barrier Reef.

The news coming out of world capitals makes it clear that we need more than lobbying by environmentalists to get the changes the science demands. We need a movement, a groundswell, to give those lobbyists the clout they need. But we can make it happen only if we join together fast.