David Appell has a post on What if GW Were Natural? but I think he misses the main point: if its natural, then there is no reason to expect it to continue. If its anthropogenic, the we have a fairly good idea of the various forcing factors and can take a reasonable stab at predicting the future. If its natural, then for some reason GHGs produce less forcing that we expect, and unknown natural forcings produce more, and we have no basis at all for prediction.


  1. #1 Roger Pielke, Jr.


    You write, “if its natural, then there is no reason to expect it to continue.”

    Not necessarily. What if (hypothetically) the solar “constant” were to be steadily increasing? That would be natural, and perhaps reasonably predictable. Asking how we’d respond in such a counter-factual is worth doing becuase it reveals some oft-unexamined assumptions.

    That is what I did in this paper;-)

    Pielke, Jr., R.A., 2005. Misdefining ”climate change”: consequences for science and action, Environmental Science & Policy, Vol. 8, pp. 548-561.

    [What you say is possible. However, if it were natural, that would mean we didn’t understand the forcing, so (assuming we could predict future solar inc) we’d have to go with some empirical relationship. Which would be quite possible. But I’m somewhat dubious about predicting future solar, so I think that *if* you knew the recent inc was solar, you’d be stuck with not knowing the future forcing anyway. I’ve seen different guesses, though -W]

  2. #2 Roger Pielke, Jr.

    William- Given that some solar scientists currently think they can predict solar activity, I am sure that there would be similar claims in my hypothetical scenario.

    But that misses the more important point of the thought experiment, in my view. Under such a scenario wouldn’t we still want to reduce CO2 to limit climate change, (e.g., to compensate for the increase in forcing from the sun) or geoengineer or adapt or whatever?

    If the impacts are bad, why wouldn’t we still want to respond?

    [*If* the current warming were natural, the the CO2 forcing would have to be small, so why would you bother to reduce it in the future? Of course you’d have to revise a whole lot of other stuff to in order to make sense of CO2 having such a small effect.

    As to predicting solar… yes I know some people think they can predict it. I don’t think those claims have any great credibility though. I can’t remember much specific, but I think some predict + and others -; possibly over different timescales though -W]

  3. #3 Lubos Motl

    Both of you are missing the point. It’s completely obvious – and the NAS panel has explicitly said this point in their recent report, too – that if (and because) a larger part (or most) of the recent warming has a natural origin, it cannot change our predictions in either direction. It just means that the error margins become bigger and the correlation of climate with politics smaller.

    [A bit of light comedy is always welcome -W]

  4. #4 James Annan

    IMO it’s pretty clear that the difference of opinion is in how best to interpret the rather vague hypothetical “if GW were natural” rather than in how to react to any specific set of facts…

  5. #5 Luboš Motl

    William, I doubt that you will be ever able to comprehend the reasons, but what I wrote is not a comedy but the only meaningful answer that a scientist can reach, and the National Academy of Sciences if you know what it is has reached the same conclusion.

    If things are natural, it may mean that they contributed positively or negatively to the recent warming. The average is zero, and the average future predictions are unchanged. The only thing that changes by increasing the natural factors are the error margins. Please feel free to add another childish comment here.

    [Well I hope that made sense to you, because it made no sense to me (given we have warming, which I think even you accept, then something has to have produced it. If natural forcings, you are suggesting, have contributed negatively, then the anthro stuff would have to be stronger). But you made your position clear when it came ot the betting: although you pretend not to believe in future warming, your money says otherwise -W]

  6. #6 John McCormick

    So, lets take the natural warming hypothesis one step closer to the edge. Warming does have natural causes.

    CO2 emissions have natural causes as well; and also anthropogenic sources, i.e., land use, fossil fuel combustion, intentional burning, etc.

    Now, we can sit back and watch the natural warming forces at work while we measure the increasing acidity of the oceans and diminished capacity of oceans to provide sinks for our CO2 contributions to the atmosphere which, I believe (unless atmospheric chemistry science is a fraud) will add to the warming and trigger positive feedback of CO2 and CH4 from melting tundra and permafrost.

    Or, am I mising something here?

  7. #7 Martin Lewitt

    If more of the recent warming is natural, then the models that got it wrong will have to be corrected. The same model errors which had them attributing too much warming to anthro GHGs, when corrected, will reduce the temperature increases projected using future GHG emmisions scenerios. The chief positive anthro forcings are projected to increase and solar forcing is projected to decrease over the next 25 to 50 years, even if the errors in projections have not changed, the projections themselves will have changed and need to mitigate will be reduced or eliminated. The model improvements should reduce the error in future projections, and the model projections should converge, since despite their relatively independent development, the underlying physics is the same. The acidity of the oceans remain an issue however, they don’t seem as immediate a concern as some of the more exteme temperature and sea level projections.

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