They said that 350 parts per million CO2 was the upper limit if we wished to have a planet “similar to the one on which civilization developed and to which life on earth is adapted.” That number is unrefuted; indeed, a constant flow of additional evidence supports it from many directions. Just this week, for instance, oceanographers reported that longterm atmospheric levels above 360 ppm would doom coral reefs worldwide.
It is, therefore, no longer possible to defend higher targets as a bulwark against catastrophic change. The Global Humanitarian Forum reported recently that climate change was already claiming 300,000 lives per year—that should qualify as catastrophic. A new Oxfam report makes very clear the degree of suffering caused by the warming we've already seen, and adds "Warming of 2 degrees C entails a devastating future for at least 600 million people," almost all of them innocent of any role in causing this trouble. If the Arctic melts at less than one degree, then two degrees can’t be a real target. This is simply how science works. New information drives out the old.
You could, logically, defend targets like 450 or 2 degrees C as the best we could hope for politically, especially if you add that they represent absolute upper limits that we must bounce back below as quickly as possible. But even that is politically problematic, because it implies—to policy makers and the general public—that we still have atmosphere left in which to put more carbon, and time to gradually adjust policies. We don’t—not with feedback loops like methane release starting to kick in with a vengeance. It is, we
think, far wiser to tell people the best science, in part because it motivates action. It’s the difference between a doctor telling you that you really should think about changing your diet and a doctor telling you your cholesterol is already too high and a heart attack is imminent. The second scenario is the one that gets your attention.
A number of small island nations and less developed country governments have joined leaders like Al Gore in enunciating firmly the 350 target, and equating it with survival. Climate coalition groups like TckTckTck have also endorsed the target, as have a growing coalition of hundreds of organizational allies.
Here's the important thing to remember: arguing for 350 is not making “the perfect the enemy of the good.” It’s making the necessary the enemy of the convenient. We were aware that we wouldn't get an agreement in Copenhagen that rapidly returns us to 350—even if we do everything right it will take decades for the world's oceans and forests to absorb the excess carbon we've already poured into the atmosphere. But that's why we've got to get going now—and at the very least we have a number to explain why the agreement that did emerge is insufficient and needs to be revised quickly and regularly. We can use it to make Copenhagen a real beginning, not an end for years to come the way Kyoto was.
In the end, everyone needs to remember that the goal at Copenhagen was not to get a “victory,” not to sign an agreement. It’s to actually take steps commensurate with the problem. And those steps are dictated, in the end, by science. This negotiation, on the surface, is between America and China and the EU and India and the developing world; between industry and environmentalists; between old and new technology. But at root the real negotiation is between human beings on the one hand, and physics and chemistry on the other. Physics and chemistry have laid their cards on the table: above 350 the world doesn’t work. They are not going to negotiate further. It’s up to us to figure out, this year and in the years ahead, how to meet their bottom line.