Wednesday, July 01, 2015
Once more: Climate was highly variable in prehistory too
Findings from Finland yesterday, South America today. Another finding of big climate swings. Also found below: Insolation (the sun) was primary driver of tropical S. American climate in the past 120,000 years. Just the first half of the unusually long abstract below. The second half deals with models
Nature and causes of Quaternary climate variation of tropical South America
Paul A. Baker et al.
This selective review of the Quaternary paleoclimate of the South American summer monsoon (SASM) domain presents viewpoints regarding a range of key issues in the field, many of which are unresolved and some of which are controversial. (1) El Niño-Southern Oscillation variability, while the most important global-scale mode of interannual climate variation, is insufficient to explain most of the variation of tropical South American climate observed in both the instrumental and the paleoclimate records. (2) Significant climate variation in tropical South America occurs on seasonal to orbital (i.e. multi-millennial) time scales as a result of sea-surface temperature (SST) variation and ocean–atmosphere interactions of the tropical Atlantic. (3) Decadal-scale climate variability, linked with this tropical Atlantic variability, has been a persistent characteristic of climate in tropical South America for at least the past half millennium, and likely, far beyond. (4) Centennial-to-millennial climate events in tropical South America were of longer duration and, perhaps, larger amplitude than any observed in the instrumental period, which is little more than a century long in tropical South America. These were superimposed upon both precession-paced insolation changes that caused significant variation in SASM precipitation and eccentricity-paced global glacial boundary conditions that caused significant changes in the tropical South American moisture balance. As a result, river sediment and water discharge increased and decreased across tropical South America, lake levels rose and fell, paleolakes arose and disappeared on the Altiplano, glaciers waxed and waned in the tropical Andes, and the tropical rainforest underwent significant changes in composition and extent.
Quaternary Science Reviews. Volume 124, 15 September 2015, Pages 31–47
There's nothing unusual about current levels of CO2
Even though there were no coal-burning power stations in the Eocene. The late Eocene interglacial was ~100,000 years ago. Data from China
The pCO2 estimates of the late Eocene in South China based on stomatal density of Nageia Gaertner leaves
X.-Y. Liu et al.
Late Eocene pCO2 concentration is estimated based on the species of Nageia maomingensis Jin et Liu from the late Eocene of Maoming Basin, Guangdong Province. This is the first paleoatmospheric estimates for the late Eocene of South China using stomatal data. Studies of stomatal density (SD) and stomatal index (SI) with N. motleyi (Parl.) De Laub., the nearest living equivalent species of the fossil, indicate that the SD inversely responds to atmospheric CO2 concentration, while SI has almost no relationships with atmospheric CO2 concentration. Therefore, the pCO2 concentration is reconstructed based on the SD of the fossil leaves in comparison with N. motleyi. Results suggest that the mean CO2 concentration was 391.0 ± 41.1 ppmv or 386.5 ± 27.8 ppmv during the late Eocene, which is significantly higher than the CO2 concentrations documented from 1968 to 1955 but similar to the values for current atmosphere indicating that the Carbon Dioxide levels during that the late Eocene at that time may have been similar to today.
Clim. Past Discuss., 11, 2615-2647, 2015
Posted by John J. Ray (M.A.; Ph.D.).