A paper published today in Climate of the Past finds climate models are unable to reproduce the temperatures of the mid-Miocene Climatic Optimum when CO2 levels were about the same as today [400 ppm]. The authors find the models simulate a global mean temperature 4°C less than determined from climate proxies, and "an equator to pole temperature gradient which is at least ~ 10°C larger than the reconstruction from proxies." The authors acknowledge "a major climate problem" between the model world and the real world reconstructions. The paper adds to hundreds of other peer reviewed publications indicating that there are fundamental flaws in the climate models, including sensitivity to CO2, feedbacks, and heat transfer assumptions. Prior papers have also found that climate models are unable to reproduce the Medieval Warming Period, or the 20th & 21st century climate, much less the future.
Clim. Past Discuss., 9, 3489-3518, 2013
1Earth, Atmospheric, and Planetary Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907, USA
2Purdue Climate Change Research Center, Purdue University, Mann Hall 203 S. Martin Jischke Drive, West Lafayette, IN 47907, USA
Abstract. The mid-Miocene Climatic Optimum (MMCO) is an intriguing climatic period due to its above-modern temperatures in mid-to-high latitudes in the presence of close-to-modern CO2 concentrations. We use the recently released Community Earth System Model (CESM1.0) with a slab ocean to simulate this warm period, incorporating recent Miocene CO2 reconstructions of 400 ppm. We simulate a global mean annual temperature (MAT) of 18 °C, ~4 °C above the pre-industrial value, but 4 °C colder than the global Miocene MAT we calculate from climate proxies. Sensitivity tests reveal that the inclusion of a reduced Antarctic ice sheet, eastern equatorial Pacific Ocean temperature anomalies, increased CO2 to 560 ppm, and variations in obliquity only marginally improve model-data agreement. All MMCO simulations have an equator to pole temperature gradient which is at least ~ 10 °C larger than the reconstruction from proxies. The MMCO simulation most comparable to the proxy records requires a CO2 concentration of 800 ppm. Our results illustrate that MMCO warmth is not reproducible using the CESM1.0 forced with CO2 concentrations reconstructed for the Miocene or including various proposed Earth system feedbacks; the remaining discrepancy in the MAT is comparable to that introduced by a CO2 doubling. The models tendency to underestimate proxy derived global MAT and overestimate the equator to pole temperature gradient suggests a major climate problem in the MMCO akin to those in the Eocene. Our results imply that this latest model, as with previous generations of climate models, is either not sensitive enough or additional forcings remain missing that explain half of the anomalous warmth and pronounced polar amplification of the MMCO.