Global warming and rainfall: Lessons from an analysis of Mid-Miocene climate data

The Mid-Miocene Climatic Optimum (MMCO) has been regarded as an analog for future global warming due to its scale of warming being equivalent to the warming predicted for the next century by the International Panel on Climate Change (IPCC)'s fourth report. However, little is known about how the MMCO influenced paleoprecipitation in central China. In this study, two pollen floras from the eastern Longzhong Basin, northern central China, were quantitatively analyzed to reconstruct the climatic conditions likely during the MMCO. The paleoclimatic parameters obtained by applying the Coexistence Approach (CoA) to these two palynological assemblages showed that the mean annual temperature (MAT, 16.6 degrees C) for the MMCO was 5.7 degrees C higher than the present-day MAT (10.9 degrees C), and that mean annual precipitation (MAP, 955.4 mm) was 413.5 mm higher than at present (541.9 mm), indicating a much warmer and wetter climate. The higher mean temperature for the coldest month (CMT) and the minimum monthly precipitation (MiMP) values also indicate a warmer and wetter coldest and driest month, respectively, and thus suggest the prevalence of a more balanced seasonal paleoclimate in northern central China. These climatic conditions are equivalent to higher global temperatures of similar to 5-6 degrees C during the MMCO. This finding would imply that precipitation in northern central China will increase in the context of ongoing global warming.