Are we 'safe' with 2 degrees of warming?

That is, as the Dane said, the question.

The short answer is "nobody knows," of course. The ice core records suggest that we're adding CO2 to the atmosphere faster than the planet has ever seen before. That doesn't necessarily mean that the consequences of doing so ;;;; planetary warming and extreme drought in dry areas, for example ;;;; will be felt soon, or at all. But in the past, such consequences sooner or later come about. And it would be foolish to operate on the assumption that the Earth has some of kind of hitherto undiscovered compensatory mechanism that spares us from them.

Which is why politicians would prefer climatologists tell them just what kind of warming civilization can handle and what we can't. And that was the question that occupied some of the brightest minds on the planet last week in Copenhagen. Here's climatologist Stefan Rahmstorf at the conference's closing session:

I want to emphasize that when as scientists we talk about those two degrees, that really is a kind of upper limit that we really should not cross. I personally as a climate scientists, I could not honestly go and tell the public that two degrees warming is safe. We're already seeing a lot of impacts of the 0.7 degrees warming that we've had so far. So I consider two degrees not safe, and John Schellnhuber this morning asked about the question "Is Russian Roulette dangerous?" and in RR you have a one in six chance of something terrible happening, I think that when we go to two degrees we probably have more than a one in six chance of really bad impacts occurring.

Recall that Europe recently agreed to design emissions reductions strategies that are designed to limit the consequent warming to 2 °C. and it's easy to understand why the prime minister of Denmark, Anders Fogh Rasmussen, would respond in this manner:

I need some concrete advice now. Stefan Rahmstorf said two degrees -- the two-degree target -- is not safe. So, now I need to know from the panel, can we as politicians still rely on the IPCC recommendations or not? What you're telling me, is it that we should set the bar even higher? I need to know that. And I'll tell you why. I have -- we have had a very hard battle within the European Union, and finally we decided on the 2 °C target. It's been a real challenge to reach that point. And now you tell me "it's not enough." Now I need to know, and I need to know today, is it enough, or do we have to change this target, because it's fundamental. We have now nine months left before a very, very important meeting in this room. It will be a real challenge - and now I think the scientific world has to make an agreement with itself - what is the real platform for politicians?

The moderator of the session Katherine Richardson, felt it necessary to make a clarification:

Richardson: And here you see a beautiful example of miscommunication. Because Stefan Rahmstorf did not say it wasn't safe, he said, "I can't say it is safe." And here, this is where we get into these nuances.

Rasmussen: Yes, but as a politician, I have to make a decision.

Rasmussen didn't get a lot more help from the scientists. Rahmstorf added that "Two degrees is really an upper limit, and its not something that, you know, we aim for two degrees but it's OK if we end up at three." Collectively, the conference participants' best advice was distilled down to this :

Key Message 1: Climatic Trends
Recent observations confirm that, given high rates of observed emissions, the worst-case IPCC scenario trajectories (or even worse) are being realised. For many key parameters, the climate system is already moving beyond the patterns of natural variability within which our society and economy have developed and thrived. These parameters include global mean surface temperature, sea-level rise, ocean and ice sheet dynamics, ocean acidification, and extreme climatic events. There is a significant risk that many of the trends will accelerate, leading to an increasing risk of abrupt or irreversible climatic shifts.

British climate activist and columnist George Monbiot, however, says there's a difference between the official word and what the climatology community is really thinking, a distinction that might help politicians like Rasmussen make the decisions they have to make. If 2 °C (~4 °F) is a point beyond which we don't want to go, then the real question is, can we avoid that point, given that we've already seen a rise of 0.7 °C, with another similar amount irrevocably in the literal and figurative pipeline? Monbiot writes:

Quietly in public, loudly in private, climate scientists everywhere are saying the same thing: it's over. The years in which more than two degrees of global warming could have been prevented have passed, the opportunities squandered by denial and delay. On current trajectories we'll be lucky to get away with four degrees. Mitigation (limiting greenhouse gas pollution) has failed; now we must adapt to what nature sends our way. If we can.

Does that statement accurately reflect the thinking of the climatology community? I asked Johnathan Bamber, a climatologist who was in Copenhagen last week. His reply:

I am not sure I can completely sign up to the statement [by Monbiot] BUT, the point he is making (I think) is that there is a long lag or latency in the climate system and it may be that if we cut our CO2 emissions to zero tomorrow, the world would still likely warm by something like 2 degs as the CO2 residence time in the atmosphere is long.... There are many uncertainties in this, not related to climate sensitivity, but to how the biosphere and climate system respond to any warming.

If we want to avert higher temperature rises then we are looking at CCS, sequestration and maybe geo-engineering solutions....

To me, it all suggests we might still have at our technological disposal the theoretical capacity to keep the temperature rise to 2 °C. More or less. Whether it's politically possible is an entirely different question. But we don't control a thermostat with degrees conveniently ticked off on a dial or LCD screen. Instead we have control of fossil-fuel emissions, the rate of deforestation, and the agricultural methane releases that are the primary causes of the warming. We measure those in tonnes of carbon. But we still don't know just how many tonnes of the stuff the planet can handle before we cause enough warming to exceed 2 degrees.

The consensus, again lifted from the Copenhagen discussion, is we should probably cut our current emission of ~10 billion tonnes a year in half globally, and by more than 80 % in the developed world. That hasn't really changed over the last few years. So when Rasmussen worries about moving targets in terms of how much warming the Earth can handle, maybe he's asking for the wrong numbers.

New Scientist's Catherine Brahic, who was also at the conference, wrote this:

John Ashton, who is the UK government's special representative on climate change, says it's "wrong and dangerous" for scientists to confuse politicians over the 2 °C target, and this "will make it harder to get the intensity and urgency of effort required".

Martin Parry of the Grantham Research Institute on Climate Change and the Environment in London ... argues that politicians need to ignore the indecision that came out of the meeting and stick to their targets. "Studies continue and there isn't time to take a careful evaluation of all these, let alone get government agreement so science is working back-to-back with policy," says Parry.

I think I'm beginning to understand the Obama plan on climate change mitigation. Emissions reductions are not the organizing principle. Instead he's slipping such stuff into his larger budget and foreign-policy strategies. If we don't have the luxury of the time it takes to build political coalitions and produce some kind of scientifically based consensus on our targets, then just start doing what needs to be done and what is feasible now. Worry about treaties and whatnot later.

If this is the case, then the big political meeting in Copenhagen at the end of the year, the one where the world is supposed to come up with a successor to the Kyoto Protocol, may be a different kind of show than many people expect. If Europe is already on board with a plan to cut emissions by 20 or 30 or even 40 % by 2020, and the U.S. has its own policies in place, then Copenhagen will be more about bring the Chinese and Indians on aboard.