The big international climate conferences, at least the ones I’ve been to in Kyoto, the Hague, and elsewhere, are pretty much the same: caffeinated, adrenalized, endless, chaotic, and incredibly hard to read. Much goes on behind closed doors, and small signals from the big players at the last minute generally make the most difference.

I’m not going to Poznan until next week, for the last few days of this conference. And in an odd way, it’s been easier to figure out the proceedings from a distance to make out the forest for the trees.

The biggest news so far, I think, has been that some of the parties have absorbed the really salient fact of the last 18 months: the science is changing and changing fast, and the old negotiating positions no longer work, the old lines in the sand are being erased, as it were, by the rising tide.

For almost a decade now, the ‘tough’ position has been that we shouldn’t tolerate more than 450 parts per million co2 in the atmosphere, nor more than a two degree Celsius rise in temperature. When the Europeans proposed those numbers in the 1990s, they were more stringent than the old targets a vague attempt to avoid a doubling of the atmospheric concentration, which was 275 parts per million before we started burning coal and gas and oil. By now they’re the consensus middle ground.

But 18 months ago the Arctic melted, decades ahead of schedule and with only 387 parts per million co2 in the atmosphere. Last January, spurred by Jim Hansen’s new research, we launched 350.org, arguing that the old numbers were obsolete. Arguing that we finally had a science-based red line to consider. No one likes to shift their position not governments, and not even climate campaigners, who had done yeoman work to get 450 accepted as a goal. But we’ve seen subtle shifts all year and this week they broke into the open.

On Tuesday, the Least Developed Countries offered their “shared vision” of what a treaty should look like, and they were adamant that 350 ppm needed to be the target. The 49 LDCs comprise a mix of African, Asian, and a few other of the poorest nations and the ones most vulnerable to sea-level rise, the spread of mosquitoes, the loss of drinking water from glaciers, and so on. Earlier the same day, the International Youth Climate Network also endorsed a 350 target. One way of looking at it: those who will be hit first and hardest by climate change, and those who will live with it the longest, have figured out what the bottom line really is.

That understanding will spread, inexorably, as the year goes on towards Copenhagen. It may or may not prove possible to reach a treaty that actually heads us in the necessary direction (Hansen’s calculations say it requires coal-burning to cease by 2030, which is a tall order). But at the very least it will become progressively harder to pretend that we don’t know where the edge of the cliff actually is.