Recent Lessons from the Past

June 4, 2014 5:37 am3 comments

Recently a german taxi driver asked me if climate hasn’t been changing in the past with similar warm periods as the one we have now. After getting back home to Corvallis, Oregon, I read a letter to the editor of our local newspaper claiming that it was much warmer than today during the medieval warm period. What has the most recent science to say? As the figure below shows global average temperatures haven’t been as high as today for about 5,000 years. Going back even further in time it was warmer or similar as today during the last interglacial (Eemian) period about 120,000 years ago. These warm periods had natural causes (humans didn’t play a role) but the current human-made warming is much faster than past natural changes.

Global surface temperature (anomaly from 1960-1990 average) reconstructions for the past 9000 years (Marcott et al. 2013), for the past 2,000 years (PAGES 2k), and observed for the past 150 years (Instrumental data from HadCRUT4) and the last 30 years (star). From Kaufman et al. (2013).

Global surface temperature (anomaly from 1960-1990 average) reconstructions for the past 9000 years (Marcott et al. 2013), for the past 2,000 years (PAGES 2k), and observed for the past 150 yrs (Instrumental data from HadCRUT4) and the last 30 years (star). From Kaufman et al. (2013).

Both the Marcott et al. and the PAGES 2k reconstructions, which are independent from each other, agree that global climate has cooled slowly during the past several thousands years. The so called medieval warm period was probably just a regional phenomenon in Europe, the North Atlantic and North America, but it did not affect global temperatures and it was not warmer than today. In fact, it was about 0.3 deg C cooler than the last 30 years.

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  • BTW, that spike in the Marcott et al. reconstruction (nearly vertical light brown line at the end) is an artifact of a very small number of proxies and should be disregarded in favor of the smoothed instrumental data curve.

    The smoothing washes out the most recent warming, hence the “last 30 years” point is also shown.

    People who don’t believe in conservation of energy regard the past 30 years as a temporary, possibly cyclical, warm period. For them, it would be inappropriate to compare the “last 30 years” to the Marcott et al reconstruction, since the reconstruction can only resolve time scales of about 500 years or longer.

    People who do believe in conservation of energy recognize the “last 30 years” point as a mere stepping stone to even warmer temperatures in the future, indicating that we’re on a trajectory to easily exceed normal conditions during the peak warmth of the Holocene.

  • True, Marcott et al does not have decadal resolution, but the PAGES reconstruction does. So, comparison of the “last 30 years” with PAGES is appropriate.

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  • http://atmo.tamu.edu/profile/JNielsen-Gammon John Nielsen-Gammon

    BTW, that spike in the Marcott et al. reconstruction (nearly vertical light brown line at the end) is an artifact of a very small number of proxies and should be disregarded in favor of the smoothed instrumental data curve.

    The smoothing washes out the most recent warming, hence the “last 30 years” point is also shown.

    People who don’t believe in conservation of energy regard the past 30 years as a temporary, possibly cyclical, warm period. For them, it would be inappropriate to compare the “last 30 years” to the Marcott et al reconstruction, since the reconstruction can only resolve time scales of about 500 years or longer.

    People who do believe in conservation of energy recognize the “last 30 years” point as a mere stepping stone to even warmer temperatures in the future, indicating that we’re on a trajectory to easily exceed normal conditions during the peak warmth of the Holocene.

    • http://ourchangingclimate.wordpress.com/ Bart Verheggen

      To go further on the very good point that John N-G makes, the “wheelchair” figure by Jos Hagelaars shows how the paleo-temperatures compare to what’s projected for the rest of the century (and also extended further backwards in time using Shakun’s data): http://ourchangingclimate.wordpress.com/2013/03/19/the-two-epochs-of-marcott/

  • http://ceoas.oregonstate.edu/profile/schmittner/ Andreas Schmittner

    True, Marcott et al does not have decadal resolution, but the PAGES reconstruction does. So, comparison of the “last 30 years” with PAGES is appropriate.

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