Parting company with McKibben and, maybe, Hansen

The nation’s top climate scientist, NASA’s James Hansen, apparently now believes “the safe upper limit for atmospheric CO2 is no more than 350 ppm,” according to an op-ed by the the great environmental writer Bill McKibben. Yet while preindustrial levels were 280, we’re now already at more than 380 and rising 2 ppm a year!

Like many people, in the 1990s I believed 550 was the target needed to avoid climate catastrophe — but now it’s clear that

  1. 550 ppm would lead to the greatest disaster ever experienced by human civilization — returning us to temperatures last seen when sea levels were some 80 feet higher. This is especially true because….
  2. Long before we hit 550, major carbon cycle feedbacks — the loss of carbon from the tundra and the Amazon, the saturation of the ocean sink (already beginning) would almost certainly kick in to high gear, inevitably pushing us to much, much higher CO2 levels (see here and here and my book).

Exactly when those feedbacks seriously kick in is the rub. No one knows for sure, but based on my review of the literature and interviews of leading climate scientists, somewhere between 400 and 500 ppm seems most likely. It could be lower, but it probably couldn’t be much higher.

So I, like the Center for American Progress and the world’s top climate scientists, now believe 450 ppm is the upper bound. That said, I have spent two decades managing, analyzing, researching, and writing about climate solutions and can state with some confidence that:

  1. Staying below 450 ppm is technologically doable, but would be the greatest achievement in the history of the human race, by far. It would require a global effort sustained for decades comparable to what the U.S. did for just the few years of World War II (the biggest obstacle is not technological, but political — conservatives currently would never let progressives and moderates pursue such a strategy).
  2. If 350 ppm is needed (and I’m not at all sure it is) then the deniers and delayers have won, since such a target is hopeless.

In 2008, I will devote a fair amount of ink bits to laying out the solution (there really is only one), but to understand why 450 is so hard, and 350 all but inconceivable, let’s look at the odd way McKibben describes the solution:

And we’re already past 350. Does that mean we’re doomed? Not quite. Not any more than your doctor telling you that your cholesterol is way too high means the game is over. Much like the way your body will thin its blood if you give up cheese fries, so the Earth naturally gets rid of some of its CO2each year. We just need to stop putting more in and, over time, the number will fall, perhaps fast enough to avert the worst damage.

Not a great analogy. Yes, CO2 concentrations will probably start dropping once we cut emissions 80% from current levels. But you can change your entire diet — cut cholestorol intake or carbohydrates 80% or more — tomorrow. Humanity cannot, however, cut its hydrocarbon diet 80% tomorrow or even, realistically, in 10 years. That would require replacing the world’s entire energy infrastructure — power plants, cars, planes, factories, fueling infrastructure, large parts of homes and commercial buildings — while simultaneously deploying a hydrocarbon-free energy system in the rapidly-growing developing world.

McKibben certainly understands some of the difficulty:

That “just,” of course, hides the biggest political and economic task we’ve ever faced: weaning ourselves from coal, gas and oil. The difference between 550 and 350 is that the weaning has to happen now, and everywhere. No more passing the buck. The gentle measures bandied about at Bali, themselves way too much for the Bush administration, don’t come close. Hansen called for an immediate ban on new coal-fired power plants that don’t capture carbon, the phaseout of old coal-fired generators, and a tax on carbon high enough to make sure that we leave tar sands and oil shale in the ground. To use the medical analogy, we’re not talking statins to drop your cholesterol; we’re talking huge changes in every aspect of your daily life.

A better analogy might be stomach stapling, but even that doesn’t do justice to what we would need to do to get to 350. Hansen’s three proposals are a drop in the bucket. Dealing with electricity is trivial compared to dealing with transportation.

Suppose we could get global carbon emissions to peak in 2020 at 10 billion tons, level off for a few years, and then decline 3% per year afterwards. No easy feat since emissions are currently at 8 billion and rising over 3% per year. China and India, for instance, would have to agree to a hard emissions cap in 2020. Rich countries would need to start slashing emissions immediately. CO2 concentrations in 2020 would be about 410 ppm (and rising over 2 ppm a year).

Around 2050, we’d be at 5 billion tons and very likely over 450 ppm, rising over 1 ppm a year. But remember, we need to average 5 billion tons a year for the entire century just to stabilize at 450 ppm (according to the IPCC — and that is probably a best-case scenario)!

So the scenario I laid out won’t get us to below 450 (I have a long discussion in the book about why beating 500 ppm is so hard if we try to do it the tradtional [i.e. slow] way). That’s why I say 450 needs a World War II scale effort starting in the next decade. I think 350 ppm is simply beyond serious practical and political consideration. You might as well tell people we need to develop a time machine to go back 20 years and warn the world that we need to start cutting emissions then … then again, who would listen.? [And who would we send back, anyway? That’s an interesting parlor game all by itself]. McKibben ends:

But at least we’re homing in on the right number. Three hundred and fifty is the number every person needs to know.

I part company with him here. I haven’t talked to Hansen yet and I’ll reserve further judgment until I see a paper or PPT by him.

Since beating 450 ppm is doable and certainly necessary — that’s where I draw the line. One advantage of pursuing 450 is that if we do get some sort of unexpected breakthrough — a cheap and practical way to draw CO2 out of the air (that doesn’t use a lot of land, water, or energy) and stick it someplace permanent — then we would have a system in place to deploy it fast enough to perhaps get to below 400 ppm. And even if turns out 450 doesn’t avert catastrophe, it will surely slow down the impacts enough to make adaptation more viable.

So I’m sticking with 450. Implausible? Yes. Impossible? No. Less costly than inaction? By far.


29 Responses to Parting company with McKibben and, maybe, Hansen

  1. John Mashey says:

    I assume you have Kharecha & Hansen, “Implications of “peak oil” for atmospheric CO2 and climate,”
    [Not yet published.]

    See especially Fig 4: I don’t see anything in there near 350ppm.

    That certainly uses 450ppm, maybe Hansen changed his mind later, or maybe he’s just saying it’s more urgent than he thought a little while ago, or maybe McKibben’s description didn’t catch the nuances.

    Most of what he says and and what you say look pretty similar to me.

    Finally, for all of us, when we throw these numbers around, it would be nice to clearly distinguish between:

    (a) Peak CO2
    (b) Longer-term CO2.

    Rather than just quoting a number: we know this depends on trajectory, not just a peak number, i.e., it doesn’t do us much good if we stop at 450 and stay there, as teh climate system will be in disequilibrium for a long time.

    It might be prefect plausible to think that there’s no likely way we can keep (a) much below 450, but maybe Hansen is saying that we’d better have a plan to get it back down to 350 (b).

  2. Ron says:

    Maybe this is a better thread for this post. I think it got lost in that looong thread that began with the Inhofe piece.

    Here it is again:

    Oil and coal reserves are a finite resource; the supply will eventually run short or run out. Correct?

    I wonder what a worst case scenario would look like – in other words, what if oil and coal use continued unchecked until it was gone. How long would that be? What would the projected warming look like? How long after it ran out would climate return to ‘normal’?

    This would be an important calculation under a few different scenarios, all assuming the CO2 hypothesis is valid:

    First, if we libertarians had our way, and we actually lived with a non-coercive government, we might not be able to take any action on climate. That’s a purely hypothetical case, of course, since we don’t live under a non-coercive government.

    Second, governments might not be able to reduce emissions enough to make much of a difference. If so, the ‘worst case’ calculation needs to be done.

    Third, assuming we really are seeing a warming trend, science may eventually find that the phenomenon is being driven by a combination of human and natural causes, in which case our global warming mitigation measures might be ineffective. In that case it might make more sense to spend money on adaptation measures and basically just let the oil and coal run out ‘on their own’.

    So, what would we be looking at? A hundred years of a warming trend? More? How high would the average rise? How long after the carbon-intensive fuels ran out would climate start to rebound?

    One way or another, if we are running out of fossil fuels, the problem of excess CO2 will eventually go away even if we do nothing. Or nothing effective.

    How long would this take and what would be the interim effects?

  3. David B. Benson says:

    One way to remove carbon from the acctive carbon cycle is to produce biocoal, via hydrothermal carbonization, and then sequester it in abandoned mines or carbon landfills. I don’t actually known the cost, but about US$ 100 per tonne is approximately correct, at least at the beginning.

    Assuming now additional carbon is added to the active carbon cycle, removing 182 billion tonnes of carbon would restore the concentration to about 350 ppm. You do the arithmetic.

  4. David B. Benson says:

    Er, assuming NO additional carbon…

  5. Ronald says:

    James Hansen has written before that we can get all the natural gas and oil out of the ground and we might be below the C02 tipping points, but not coal. If we take out the coal, we’ll be in C02 trouble. We would also be in trouble if we took out the oil shale and the tar sands.

  6. Paul K says:

    Dr. Hansen has recently said we could possibly be at or just beyond the tipping point so this quote is not out of line. If he is correct, we don’t have ten or five or even two years to stop CO2 in its tracks. No public policy, no matter how effective it may be, can be put in place quickly enough to get the kind of reductions needed right now. While I’m not quite ready to give up my skepticism, even a 30% chance Dr. Hansen is correct would, I think, compel me to listen to him. Plus, I see a vital need to drastically reduce the use of fossil fuels regardless of global warming. If it also turns out to be the best way to reduce CO2, well that’s great too.

    One of the recommendations made by Al Gore is for small decentralized all the way down to the residential level electric generation. This is something the people have to do without much support from the government. It is something the people can do without that support because of good old American freedom of association.

  7. Joe says:

    I’d love to get back to 350 ppm. I’d love to play center field for the Yankees. Though neither are physically impossible, I think both are equally likely.

    I think walking back — i.e. significantly overshooting and then reducing — will be very, very hard because of the feedbacks and sink saturation. Maybe we could go to 450 in, say, 2050, and walk back to 420 in 2100, but I doubt it.

    As readers know, I have the greatest respect for Hansen. He has been right longer than anyone else. I’ll report on his paper on 350 when he publishes it.

    Ron, until you read my book and the core posts on this blog, which answer/refute most of your questions/assertions, I’m not going to answer your questions. Maybe others will.

  8. trucker says:

    In the book Six Degrees, Mr Lynas states that during the Pliocene Era atmospheric concentrations of CO2 ranged from 360 to 400 ppm raising global temperature by 3 degrees C and the polar zones much more. According to his book, winter on Ellesmere Island in Canada’s far north was 15 degrees C warmer than it is today.
    The catch was ocean levels 25 meters higher than those of today.
    If these numbers are true, perhaps this is why Dr Hansen is so concerned about that safe upper limit of 350 ppm?
    Is 25 meters a valid number?

  9. Ron says:


    In another post you said you are trying to keep the lives of the next 50 generations from being ruined.

    Is this the time frame we would be talking about if you were going to comment on my post above – 1000 to 1500 years?

  10. Ronald says:

    Climatologists have a hard enough time with making predictions to 2100, how could he comment on something 1000 to 1500 years in the future.
    You might be in one of your deceitful ‘gotcha’ modes where you want to appear to ask an innocent question, but then say ‘so you think you can predict what technology will be 1000 years from now.’
    Clearly, the 50 generations comment was that this may be a problem that could last for a long time. And clearly, the next generation is the first one we should worry about.

  11. Lou Grinzo says:

    First and foremost, let me say that people should read Joe’s book, Hell and High Water. I’m only part way through it, and it’s extremely well done. (Note to Joe: I’m assuming you don’t turn into a blithering idiot in the last part of the book.)

    Second, he talks about how behind the curve much of the climate modeling is in terms of including feedback effects–melting permafrost and tundra that releases CO2 or methane, thermal stratification of the ocean that limits its ability to absorb CO2, Arctic albedo flip, etc. Given the mind-blowing changes we’re seeing already, as in the plunge in Arctic sea ice extent this summer, I think it’s entirely possible that the “magic number” is indeed 350 ppm, and that industrial pollution (and its effects) has simply been far ahead of science all along, and science still hasn’t caught up completely.

    That better not be the case, or we’re screwed six ways from Sunday. Even the steps needed to minimize the impact with a 450 ppm magic number, as Joe details in his book, will require a Herculean effort coupled with a vastly more enlightened approach to this mess we’re still creating.

  12. Ronald says:

    I did an internet search and I found this web site giving the level of carbon dioxide in the atmosphere now and in the past. I don’t know that it is helpful to anybody, but here it is.

    Setting aside the real problems that global warming can and will bring, I think the whole idea and attempt to change our worlds use of carbon as the biggest, most interesting drama in the world. Sure we care about our family, kids, friends, and neighbors, but I mean as a world drama.

    That thought is not shared with many obviously. With the presidential candidates only asked 3 times out of 1500? questions about climate change, it hardly registers on the mainstream media. But I bet the water level rise in New York City will get some press.

  13. Ron says:

    Ronald & Lou,

    Yes, I could be in a deceitful ‘gotcha’ mode where I want to appear to ask an innocent question, but then say ‘so you think you can predict what technology will be 1000 years from now.’

    But in light of the considerable pessimism you guys are expressing, perhaps you might want to look at what I posted again.

    Maybe I should simply re-state it as ‘what if it’s too late to do anything about it?’ Would that make my questions easier to wrestle with?

    If mitigation efforts were ineffective, too-little-too-late, or not even attempted the climate effect would be the same, correct? The difference would be in actually how we used our money and government action.

    I know I ask tough questions, and express my opinions rather forcefully at times, but I don’t think anybody promised Joe a rose garden.

    Take another look at my post above and if you’re quite sure it’s not something you want to consider or respond to, then so be it.

  14. John McCormick says:

    Bill McKibben finished his op-ed with the follwoing:

    [But at least we’re homing in on the right number. Three hundred and fifty is the number every person needs to know]

    He is focused on the wrong application of 350; in the context of the world economy achieving CO2 reductions to that level, he is offering a wish and not an achievable wish at that.

    In the context of America’s near-term future, the 350 is the number of millions of citizens called the United States their home. That is a real likelihood given that U.S. fertility rate has hit a 35 year high and US population is stabilizing. The Population Council estimated the 350 million population by 2025…just 18 years and counting.

    Those 50 million new neighbors will consume energy to sustain or magnify today’s standard of living. In 2006, Americans consumed 85 quadrillion British thermal units (BTUs) of coal, oil and natural gas (284 million BTUs per capita). That energy ran our economy while adding 6 billion tons of carbon dioxide to the atmosphere and, with the help of the rest of the world’s energy users, increased CO2 steadily towards levels Dr. Jim Hansen warns will define our future. Will 350 million Americans contribute to his prophecy?

    U.S. energy use has grown, on average, 1.1 percent since 1990. Apply that rate out to 2025 and U.S. fossil fuel use will top 105 quadrillion BTUs and send 7.4 billion tons of CO2 to the atmosphere.

    I can hear the keyboards clicking with the words ‘renewable’ and ‘efficient buildings’ and ‘appliance efficiency standards’ heading towards Joe’s reply box. But, the EIA 2006 and 2007 electricity, petroleum and coal consumption data give no inidcation Americans have caught on to Dr. Hansen’s message.

    Legislation to reduce CO2 emissions hinges on national elections that deliver support to the White House and Capitol Hill. The longer we delay the harder the challenge to persuade a greater number of energy consumers to use less than we enjoyed.

    I believe what I read, observe and hear about the pace of change and impact excceding earlier model projections by 20 years or more. We have no clue how to quantify CO2 and CH4 feedback from melting permafrost and tundra.

    Personally, I am beginning to imaging the collapse of global capitalism as the sea level rises to innundate petrochemical, refineries and energy infrastructure aroung the globe. Add the massive international social turmoil of migranting refugees moving to higher land and the potential for collapse of civil society becomes likely.

    John Mashey’s comment above stated that trajectory matters. Whether it is political will, energy investments or consumer choices, the trajectories I see are all pointing in the wrong direction.

  15. Gareth says:

    Just to complicate matters a little, consider this. AR4 gives total CO2e at the moment as 455 ppm (CO2 + NOx + CH3 etc), but this is reduced to 375 ppm CO2e by aerosols, land use change etc. So we can use the current CO2 concentration as a rule of thumb for actual forcing.

    But… the things we do to reduce emissions and decarbonise the economy will tend to reduce the cooling effects. In other words, as we rush to limit the increase in CO2, we will also be making the CO2e we’ve already got more effective at warming the planet. This in effect means much steeper cuts if we are to limit both transient and equilibrium warming. I haven’t been following the emissions trajectory modelling literature, so I can’t say if this effect is being factored in, but I do know that it doesn’t make good reading for those who think 450 ppm is consistent with a 2C rise.

    My crystal ball is a bit cloudy and cracked, but it looks to me like the Arctic is about to make everything moot. If we see another big summer sea ice loss in the next year or two, the Arctic will soon (10 years?) transition to a warm state, and the northern hemisphere climate will change dramatically. Clathrates on the sea bed and methane in permafrost will add to the rate of change, and Greenland melting (and sea level rise) will accelerate, destabilising the West Antarctic ice sheet.

    The only credible response will be a rapid re-tooling of the global economy (as happened in the US in WW2), and massive aid to countries destabilised by climate change/SLR.

    So, have a happy New Year!

  16. David B. Benson says:

    Think of it this way: Currently about 8.5 billion tonnes of carbon are added to the active caron cycle each year. Assuming biocoal sequestration costs of US$ 100 per tonne to equalize that increase, that means the free-loaders are getting an 850 billion US$ free ride every year.

    That’s some externality!

  17. Albert says:

    If you disagree with their science that is one thing, but you seem to be framing this as “if we’re already over a tipping point then people would just give up, so I prefer to think that we have not reached a tipping point,” and that seems intellectually dishonest to me. The tipping points will come regardless of their political inconvenience. Whether we can prevent tragedy or not is not the only goal. There are likely to be multiple levels of tipping points. If tragedy is assured you still must act to avoid even worse tragedy. There is not a single “worst case.” There is a spectrum of disaster and we are clearly easing into the lower end of that spectrum already.

  18. Hal Levin says:

    The key to this issue is not about numbers and getting them exactly right. The uncertainties are large enough to undermine reliability in the numbers and the real arguments seems to be involved with a small number of key words in this thread: credible, feasible, disaster, sea level rise, feedbacks, tipping points, WWII scale changes, etc. The key is what kinds of observable and inescapable changes credibly attributable to climate change/chaos will result in a sufficient change of consciousness among those capable of making significantly different decisions about the various actions that can have an impact — personal and societal consumption levels, taxation, subsidies, investment in research and development, and other matters that matter.

    I don’t lay any claim to superior or even adequate knowledge, but I find feasible to be a relative term defined by the perceived necessity.

    I don’t see any reason to believe that 350 ppm is a formula for a stable climate given the current status of the Earth’s “natural” sources and sinks. What evidence is available to support this wishful target concentration as sufficient to stabilize the climate?

  19. Mitra Ardron says:

    Isn’t it about time we started setting targets based on what is NEEDED rather than what is ACHIEVABLE. Certainly we won’t achieve neccessary levels if we don’t set them as a target. If massive positive feedbacks are going to set in somewhere between 400ppm and 500ppm, doesn’t that mean that the target needs to be 400ppm or below.

    I’m not an expert on HOW to achieve it, but I’ve seen enough presentations by people like Amory Lovins and Keith Lovegrove to see how many things that conservatives call impossible *are* do-able if we start thinking outside the box. For example Keith showed a graph of replacement times for electricity generation architecture, and how its pretty close to what we need if – and only if – all new electricity infrastructure is zero (or close) in emissions, i.e. so called “Clean Coal” won’t meet the target, but if we build new requirements out of solar, wind, tidal etc then natural retirement of existing assets would meet targets.

    I believe there are similar arguments for transport, but only if you set the right standards, for new cars, now.

    AIA (Architects) set a similar standard for buildings, I think the number was that if all NEW buildings were 50% or less of the median emissions then natural building replacement would meet required building emission reductions.

    So – I appeal for us not to look at ACHIEVABILITY when setting standards, look at what the science is saying, and err on the safe side, then set the incentives and regulations to inspire the ingenuity of everyone to go for it. Instead of WWII as the model, look at how fast the internet has revolutionized business when the incentives were there.

  20. Paul K says:

    Mitra Ardron is correct about needed vs achievable. It is also true, whether Joe or Hansen has the exact calamitous concentration of CO2, the target needs to be 400ppm or below. I hope Joe will adopt that number in his analyisis of technologies and policy proposals.

  21. Hal Levin says:

    I completely agree that the only acceptable approach to setting targets is to do the best we can at estimating a stable atmospheric concentration of Ceq and then look at the potential means to achieve it. Starting at 450 ppm because it’s “feasible” or “achievable” is a recipe for failure to stabilize the climate.

    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.

  22. Joe says:

    I don’t support beating 450 just because I think it is doable. I support it because it is clearly necessary based on the science. I haven’t seen any analysis that 350 is necessary, and I know it isn’t doable — at least not without divine intervention.

    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.

  23. David B. Benson says:

    Hal Levin — I have serious doubts that even as low as 280 ppm for atmospheric CO2 will stabilize the climate. However, if somehow it is possible to get that low, then there would be in place a means to get below 260 ppm and ample time to do so.

    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.

  24. Sage Sweetwood says:

    Has anyone done an update of the Princeton ‘wedges’ senarios?

    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.

  25. paulm says:

    Joe said…don’t support beating 450 just because I think it is doable. I support it because it is clearly necessary based on the science. I haven’t seen any analysis that 350 is necessary, and I know it isn’t doable — at least not without divine intervention….

    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,

  26. Earl Killian says:

    paulm, read

    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.

  27. paulm says:

    ta Earl.

    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.

  28. Joan says:

    Too bad you don’t believe that 350 is the highest that we can go. What do you need to convince you? Arctic ice melting was 25% higher last year than any time in human history, and that is not good enough. Hurricanes Katrina, Ike, and all the others are not enough? Species are dying out or migrating at a rate previously unseen. Does it have to happen in your backyard before it is real?

  29. David Lewis says:

    You’d be in England in 1938 saying it would be impossible to defeat Hitler so we all better get used to the idea of living as a conquered people under the Nazis.

    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.