Has James Hansen Accidentally Put CO2 Into Perspective?

James Hansen is both a champion and icon of climate activism. A respected scientist (I certainly respect him), he has been tireless in attempting to raise awareness of the possible effects of global warming and the human emissions that contribute to it. Sometimes he has gone overboard–but that’s a bit to be expected in a cause that he sincerely believes to be of utmost importance to us all.

He recently published a very short note acknowledging that temperatures have not risen over the past decade. There’s something in it that we might find of interest: “The 5-year mean global temperature has been flat for a decade, which we interpret as a combination of natural variability and a slowdown in the growth rate of the net climate forcing.”


He explains later, “It should be noted that the “standstill” temperature is at a much higher level than existed at any year in the prior decade except for the single year 1998, which had the strongest El Nino of the century. However, the standstill has led to a widespread assertion that “global warming has stopped”. Examination of this matter requires consideration of the principal climate forcing mechanisms that can drive climate change and the effects of stochastic (unforced) climate variability.

“The largest climate forcing is caused by increasing greenhouse gases, principally CO2 (Fig. 5). The annual increment in the greenhouse gas forcing (Fig. 5) has declined from about 0.05 W/m2 in the 1980s to about 0.035 W/m2 in recent years 8. The decline is primarily a consequence of successful phaseout of ozone-depleting gases and reduction of the growth rate of methane. Also, the airborne fraction of fossil fuel CO2 emissions has declined and the forcing per CO2 increment declines slowly as CO2 increases due to partial saturation of absorption bands, so the CO2 forcing growth rate has been steady despite the rapid growth of fossil fuel emissions.”

As I have written previously, fossil fuel emissions haven’t ‘grown rapidly’–they’ve exploded. According to CDIAC, one third of all human emissions in history have occurred since 1998–right when temperatures stopped rising.

Taking Hansen at his word (and I do and I think you should, too), we get an inkling of something important, but as yet not explicitly said.

Of course CO2 concentrations contribute to warming–that’s basic physics, using the same calculations that make our modern world possible. But they are not the control knob on the dashboard that is the prime mover of temperatures. Hansen himself writes about solar variability, aereosols (which might be increasing as the developing world continues industrialization), the relative proportion of El Nino to La Nina years, and of course the natural variability that is always present even when we cannot define it.

CO2 is one actor. Not the only one and perhaps not even the most important one. With recent stories about black soot being an easier problem to solve, perhaps this is legitimizing language from the climate guru himself–climate change has many causes. Some of them are our responsibility. One is CO2. Another is pollution, another is deforestation, another is other land use changes. Some of the causes of climate change are not human-caused.

This should encourage us to look at what we can do most effectively in the short term.

Look–I’m not suggesting that we abandon the fight against CO2 emissions. Nor am I suggesting that global warming has gone away. But here, in an important document written by a highly respected climate scientist, is essentially implicit permission to look at all of the causes and all of the potential solutions.

9 responses to “Has James Hansen Accidentally Put CO2 Into Perspective?

  1. Phasing out coal

    In most of the world, absent new mining techniques coal is fairly well constrained on the price front….so a focus on black carbon and the other issues related to coal should deliver ‘nearly’ the same impact as focusing on phasing out coal.

    Short term the best thing to do is examine and remove ‘non-economic’ barriers to alternatives to fossil fuels.

  2. Hiya Harry

    Do you have a list at hand of what you consider non-economic barriers to such alternative fuels?

    • Hi Tom,

      US AID prohibits support of ‘large hydro’ and ‘nuclear’ in any form.

      Australia won’t export uranium to India.(At least until very recently…I know they were discussing it in the last few months).

      And then there are always these clowns….whats the saying…’Perfection is the enemy of the good’


      • The Green Party platform now calls for small scale hydro. I think they define it as not backing the water up over the natural flood plain. Hydro may be another sector where technology is eliminating the reason for the argument. There was once a huge economy of scale in hydro. Optimum size is getting smaller. Granted, there are probably other good reasons to impound large reservoirs of water.
        The smaller dams may actually increase biodiversity. If you are worried about biodiversity (I am) the trick is to get the biologists in the planning stage, not stop the project.

      • Marty,

        Here is the standard on hydro projects –

        Click to access hydro-guidance-note.pdf

        The ‘trick’ in the developing world is to just call the Chinese and have them build your hydro project.

        The idea that a ‘developing country’ needs permission from a biologist from Berkeley or some UK University to act in the best interest of their people I find strange.

  3. Renewables may actually perpetuate coal use.

    First, because solar and wind are intermittent, they need back-up that is usually the cheapest fossil fuel. Gas in the US, coal for the rest of the world. Germans are building coal plants that are designed as renewable back-ups. Anti-nuclear folks are talking about phasing out all base-load power so that there is only wind, solar and their fossil back-ups.

    Secondly, the occurring phase-out of coal in the US has already lowered coal prices in Europe. The more we get renewables, the cheaper coal will be.

    Of course renewables will replace some fossil fuel use but the cases of Germany and Denmark don’t show any rapid declines. Due to nuclear phase-out Germans will increase their coal use.

    • This may be true somewhere, but in PA, Penelec has stated publicly that they cannot adjust their coal plants fast enough to compensate for the changes of wind turbine output. The turbines have saved no coal. There are places where the wind is more predictable, shorelines and prairies. But bringing the megaturbines to PA ridge lines was foolish.

  4. I love it – “the “standstill” temperature is at a much higher level than existed at any year….”
    If you want to see what a live audience would say to that statement, watch this famous Grodon Brown quote – http://www.youtube.com/watch?v=9Gi7qqvRlY0
    “There will be a rise in spending every year, in 2011 the rise will be 0%”

  5. The image is interesting as most of the charts one sees show trends etc around a baseline with no indication of the the actual temps involved. I realise these show anomalies and the baseline is the comparator, but, more often, it’s because the reason is that the ‘image’ is more important than the facts.

    So. comparing the image against an actual temperature baseline immediately brought to mind an article I saw some time ago.

    The following is relevant, I feel. Your comments would be of interest.

    International Standard Atmosphere
    Even more on the Troposphere

    The question is, of course, if we were still basing the global average temperature on the 15 degrees as listed above, what on earth (pun) is all the fuss about?

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