Paper Reviewed
Liu, Z., Zhu, J., Rosenthal, Y., Zhang, X., Otto-Bliesner, B.L., Timmermann, A., Smith, R.S., Lohmann, G., Zheng, W. and Timm, O.E. 2014. The Holocene temperature conundrum. Proceedings of the National Academy of Sciences USA 108: 10.1073/pnas.1407229111.

In an article published in the Proceedings of the National Academy of Sciences USA, Liu et al. (2014) begin by noting that "in the latest reconstruction of the global surface temperature throughout the Holocene (Marcott et al., 2013), the most striking feature is a pronounced cooling trend of ~0.5°C following the Holocene Thermal Maximum ... with the Neoglacial cooling culminating in the Little Ice Age." But they say that "this inferred global annual cooling in the Holocene is puzzling." And why is that? Because, as they answer their own question, "with no direct net contribution from the orbital insolation, the global annual mean radiative forcing in the Holocene should be dominated by the retreating ice sheets and rising atmospheric greenhouse gases, with both favoring a globally averaged warming." And they thus ask themselves the question of the day: "How can the global annual temperature exhibit a cooling trend in response to global warming forcing ... mainly in response to rising CO2 and the retreat of ice sheets?"

Extremely intrigued by this conundrum, the team of ten researchers - hailing from four different countries (China, Germany, the United States and the United Kingdom) - went on to compare the global temperature reconstruction of Marcott et al. with three different transient climate model simulations. This analysis also resulted in "a robust warming trend in current climate models" that they note was "opposite from the cooling in the Marcott et al. reconstruction," leaving us with what they called an unexplained "model-data inconsistency in global annual temperature of ~1°C."

In concluding their report, Liu et al. write that if the climatic reconstruction of Marcott et al. is correct - and there is little reason to believe otherwise - it will imply the existence of what they describe as "major biases" across the entire spectrum of what they call the "current generation of climatic models." And so we await further studies of this important - but not yet fully resolved - climatic conundrum, which would appear to be the path of prudence that should also be followed by the world's climate alarmists. Too much is at stake to rush headlong into a global initiative to dramatically reduce anthropogenic CO2 emissions without far more convincing evidence of our ability to accurately project the climatic consequences of mankind's continued mining and burning of coal, gas and oil.

Reference
Marcott, S.A., Shakun, J.D., Clark, P.U. and Mix, A.C. 2013. A reconstruction of regional and global temperature for the past 11,300 years. Science 339: 1198-1201.