Why Are Climate Alarmists Getting More Alarmed About CO2?
Lunt, D.J., Haywood, A.M., Schmidt, G.A., Salzmann, U., Valdes, P.J. and Dowsett, H.J. 2010. Earth system sensitivity inferred from Pliocene modelling and data. Nature Geosicience 3: 60-64. (Published online 6 December 2009.)
Pagani, M., Liu, Z., LaRiviere, J. and Ravelo, A.C. 2010. High earth-system climate sensitivity determined from Pliocene carbon dioxide concentrations. Nature Geoscience 3: 27-30. (Published online 20 December 2009.)
In these two papers, which appeared in Nature Geoscience, Pagani et al. (2010, but published online 20 Dec 2009) and Lunt et al. (2010, but published online 6 Dec 2009) calculated what they call "earth-system climate sensitivity," based on things that they and others had inferred about planetary conditions during the Pliocene period of some three to five million years ago.
The purported significance of their work derives from their contention that the planet's current climate sensitivity (without earth-system in front of it) -- which is defined to be the mean global temperature response to a doubling of the atmosphere's CO2 concentration "through radiative forcing and associated feedbacks," in the words of Pagani et al. -- includes only such things as "changes in water vapor concentrations, and the distributions of sea ice, clouds and aerosols," whereas earth-system climate sensitivity includes "the effects of long-term feedbacks such as changes in continental ice-sheet extent, terrestrial ecosystems and the production of greenhouse gases other than CO2." And when they consider these additional factors, both sets of scientists come up with an earth-system climate sensitivity that is, in the words of Lunt et al., "30-50% greater than the response based on those fast-adjusting components of the climate system that are used traditionally to estimate climate sensitivity," such as they say has historically been done by the IPCC.
One of the reasons for the significantly enhanced earth-system climate sensitivity derived by Pagani et al. and Lunt et al. derives from the fact that estimated atmospheric CO2 concentrations back in the Pliocene were not much greater than those of today, and that only small increases in CO2 were associated with the supposedly much larger increases in near-surface air temperature of that earlier epoch.
But what if other factors were at work back then, of which we either lack knowledge or are unable to accurately quantify? Could CO2 merely have been "along for the ride," as those other factors did what they did to increase Pliocene temperatures? And could not the same be true today, with the contemporary rise in CO2 getting an additional huge boost from the industrial activities of man?
This possibility should not be discounted; for when the scientific world is divided over the geographical extent and relative warmth of the Medieval Warm Period of only a thousand years ago, one wonders why anyone would place any faith at all in what these folks claim about the thermal state of the planet some three to five million years ago. Or when, to quote Schneider and Schneider (2010) -- who produced a "news & views" commentary on the Pagani et al. and Lunt et al. papers -- "the possibility of such low CO2 levels three to five million years ago was heatedly discussed [italics added, and does that mean argued???] at a workshop on Pliocene climate in Bordeaux, France [http://www.plioclimworkshop.com] at the end of October this year." Or when the description of the workshop states that the "causes of the termination of Pliocene warmth, including tectonic activity, oceanic reorganization, atmospheric CO2 drawdown, astronomical forcing, and marine productivity are still contradicted [italics added]." Or when Lunt et al. state that they actually neglected marine productivity in their analysis.
Clearly, these folks are making assumptions that give them what they want ... and ... they get it when they want it. Thus, their results should not be trusted, especially when they provide the primary reason for altering the way the entire world produces the energy that is required to run the engines of industry that support the planet's modern civilizations.
Schneider, B. and Schneider, R. 2010. Global warmth with little extra CO2. Nature Geoscience 3: 6-7. (Published online 20 December 2009.)