Saturday, February 12, 2011

Atmospheric CO2 Concentrations During Ancient Greenhouse Climates were Similar to those Predicted for A.D. 2100

That's the title of a paper published last year by Breecker et al. in the Proceedings of the National Academy of Sciences (Also see the commentary on the article). The key figure is this:

The yellow band are previous estimates of atmospheric CO2 concentrations based on calcium carbonate in ancient soils. The revised estimates from this paper are marked in red and are more in agreement with estimates from other sources. There is still a lot of uncertainty in these estimates as indicated by the one standard deviation band.

Because these estimates are lower they suggest that given estimated past temperatures the climate sensitivity to increased greenhouse gas concentrations is higher than would be the case given the yellow data. These new data suggest that the climate sensitivity for doubling carbon dioxide is greater than 3°C. This is what I found in my own time series analysis of data from the last two centuries (See this or this and this). Other research also increasingly seems to support long-run climate sensitivities above the often referenced 3°C.


  1. David, some of those links are broken

  2. Thanks for letting me know - I fixed the links now.

  3. David, the "approx 3°C" figure is the short-run sensitivity. Climate science textbooks put the long-run sensitivity in the neighbourhood of five to six degrees, or approximately double the immediate-response sensitivity.

    It takes time for the ice to melt, the ocean to warm, and for low-albedo forest to replace higher-albedo tundra - all positive feedbacks. The practitioners know about them, but are focused on a reasonable policy horizon - a century, rather than a millennium. Hence the three-degrees-per-doubling mantra.

    Paleoclimate evidence is about the long run. Are you saying that this paper says long-run climate sensitivity is now thought to be higher than the textbook five-or-six degrees per doubling? That would be troubling indeed.

    Update: on reading the linked commentary, I see that the paper is about resolving the long-standing difference between estimates from soil carbonate and those from other paleoclimate measures. Yet another anomaly bites the dust, and the consensus is confirmed.

  4. The forgotten perspective is the self-organizing principle of energy-systems of the example, cleaning properties. There is for certain no stochastic function whatever. Climate-system is like for example, almost every fish-system. They are overloaded.

    How can science change there views from doctrins that is contributing to nothing. Neither case, we schould act by slowly downsize the global circulation of money and use oil only for important services