Hansen’s point is that as a result of his historical studies, it has become apparent to him that 450 ppm is an ice free planet. So, he says, he was “stunned” to realize this, but an ice free planet can not in any way be described as a “safe” target civilization should aim for.

Who do you think you are? You can’t see how something can be accomplished, therefore it can’t be accomplished. Therefore, its time to DENY THE SCIENCE. You’re a joke. What is the point of calling for meeting a target, i.e. 450 ppm, that in Hansen’s words is “a recipe for global disaster”? You’re like one of these clowns who says their plan to gas 1,000,000 Jews is more moral than someone else’s plan to kill 6,000,000.

Get out of the way. Its time for you to leave the scene.

Leave whatever work you once saw that you were doing to people who have enough faith in humanity that they can find the power now to call for a solution to be found even if no one can see one now.

I a trying to get an idea on what the latest ‘consensus’ is … Hansen released the figures in April and, as here, there are a few skeptical about the level and the do ability of it!

Where are we now?… have more scientist come on board or is the core still basically the Hansen group?

Personally, I was convinced from earlier on by the historic graphs and data available on the web that we were well over the mark and will need a bit of luck on our side if we are to get through this.

The question is how fast will the ice collapse. Information is becoming apparent now that this could all start happening within the century – this rapid rate has been observed in the past.

Hansen recommends keeping CO2 levels below 400 ppm in the near term by phasing out coal burning by 2030, since that makes it feasible to return to 350 ppm in the long term. In particular, he writes, “In the Appendix we define a forest/soil drawdown scenario that reaches 50 ppm by 2150 (Fig. 6b). This scenario returns CO2 below 350 ppm late this century, after about 100 years above that level.”

Here is one way to think about our current CO2 level. Imagine your doctor told you had a cancerous tumor, but it has not yet metastasized. If you take action before it does, you have a chance to return to health with surgery, chemotherapy, and radiation. If you wait until it does metastasize then there is little hope of future health. The lack of a tumor is analogous to the 350 level or lower. The presence of the tumor is indicated by levels over 350, but it is not a death sentence unless you leave it go.

Joe what is the latest on the levels now – is Hansen still on a limb or have you and others (scientist) come to the conclusion that 350 (or better) is what is necessary?

Very nervous,
paulm

I thought that approach did a good job of translating the needed change into understandable units — ie installing solar panels equal to the surface area of Conn gets us 1/7 of the way to 550ppm.

If we can ever generate a WWII style effort, we need to translate science into very understandable lahguage.

The 350 ppm is only a step along the way. I personally propose about 315 ppm as another step, but just because this was the level enjoyed in the 1950s.

If you read my book, you’ll realize that any sober analysis of what is politically possible would say 450 is impossible. I would answer that 450 is, today, politically impossible. But it is doable, World War II style, probably with an overshoot first. The notion that the world is going to commit to 350, however, is simply untenable.

If Hansen puts out something very persuasive, I might change my mind, but in some sense it doesn’t matter. If 350 were achievable, you’d still have to do it Worl d War II style — put another way, if we have a shot at hitting 350, it’s only because we’ve done far more than what is needed to achieve 450. But either requires starting WWII-style by 2010. What are the chances of that?

Right now, I think we are headed to over 700 by 2100, thanks to the carbon cycle feedbacks and saturating sinks — and the apparent implacability of both U.S. conservatives and the Chinese leadership. And 1000 ppm isn’t out of the question at all.

Still, whether the goal is 350, 400, or 450, we all need to redouble our effort in the New Year. It would be a shame if humanity destroyed this Garden of Eden without at least some people putting up a serious fight.

When I wrote in my 11 am Dec 31 post that I didn’t see evidence that 350 ppm would result in a stable climate, I meant to suggest that nothing above that was likely to succeed and that the truly sustainable target might be below it.

To be far more explicit, what reason can anyone give to believe that a concentration significantly above 280 ppm will produce a stable climate?

Consider that the long duration of the relatively stable climate with 280 ppm occurred with a far greater proportion of forested land area available as sinks. Land use changes since 1850 have resulted in an increase in the net annual emissions of roughly 1.5 Pg/y (from ~0.5 to ~2 Pg/y). While the total net emissions from land is not large, the net increase is from 15 to 30% of the emissions from fossil fuel combustion.