29 Jun 2008

Modeling Climate Change

Check out this excellent booklet [PDF] from MSRI.* The first half is the science of climate change; the second half discusses the mathematics of modeling CC. It's written for the lay audience. Why?
both mathematicians and climate experts will need to communicate with the public, with elected officials, and with the media in a way that emphasizes the robust aspects as well as the uncertainties of climate predictions. They should be frank and forthright about the complexity of the climate system and the limitations inherent in any approximation of it. To the extent possible, they should educate the public to the fact that even the best model will produce a range of possibilities, not a single “forecast for the future.” They should prepare the public to understand that the range of possibilities may change as the models improve and as we get new data about the Earth system. This will not mean that scientists are changing their minds or contradicting themselves; it is part of the normal process of science. The very real uncertainties in the projections of the future should not be allowed to obscure the fact that climate change is occurring and cannot be ignored any longer.
Bottom Line: We should all have some notion of how CC modeling works, if only to put our trust in it.

* Mathematical Sciences Research Institute. I used to work there :)


  1. Bottom Line: We should all have some notion of how CC modeling works, if only to put our trust in it.

    Well, to be honest I intended on reading this booklet cover to cover, but my trust faded after the section on "How do we know?" starting on page 6 of the pdf.

    The booklet lists the 6 hottest years on record, which doesn't include 1934, even though that is now considered the hottest or 2nd hottest year (right?). But OK, this thing was based on a conference from last year, and maybe those revisions in the data hadn't come out yet.

    Less excusable, it shows a 400,000-year correlation of CO2 and temperatures a la Al Gore, and then explicitly says:

    Evidence from ice cores shows a
    very strong correlation between
    carbon dioxide levels and global
    temperatures. (See Figure 1.2)
    When carbon dioxide levels go up,
    so does the temperature.

    Given the lag of centuries between temperature moving and then CO2 following, you think they might have been a bit more nuanced with this claim. Yes yes, RealClimate has a long explanation of why an 800-year lag doesn't rule out causality.

    Even so, I think 99% of the people reading this report would be very confident that CO2 changed first, and then temperatures responded, over the last 400,000 years. They would probably be stunned to learn about the centuries-long lags in the relationship.

  2. Just to follow-up: In case some readers aren't familiar with the "denier" arguments, I should clarify that it's not simply that CO2 changes, and then it takes temperature 800 years to respond.

    No, it's the other way around: If you look at the chart such as the math booklet presents, it seems that over a 400,000-year timeline CO2 and temperatures move in lockstep.

    But if you zoom in, you see that actually temperatures move first, and then (800 years later) you see CO2 moving in the same direction.

    So it's not at all clear that this chart "proves" CO2 drives temperature change.


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