Milankovitch Forcing and Tree Ring Proxies

Climate Audit

Mar 2, 2021. This post was written in 2015 but, for some reason, I didn’t publish it at the time.  Seems just as valid today as when it was written.

Esper et al 2012, Orbital Forcing of Tree Ring Data pdfSI, is one of the few paleoclimate articles in past decade which really made me stop and think. It connected two obvious points:

  • high-latitude tree ring proxies are sensitive to summer (JJA, even JJ) temperature, not annual temperature.
  • high-latitude NH summer insolation, which has long had special interest as the “prime forcing” of Milankovitch theory of ice ages, had declined by ~6 w m-2 over the past 2000 years, the period covered by many popular IPCC temperature reconstructions. An amount that is approximately four times larger than anthropogenic forcing from CO2 since 1750 AD (~1.5 w m-2).

From these two points, they made plausible and compelling observation that the…

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