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CO2 lagged rising temperature in the Southern Hemisphere during last deglaciation

Author: Geoff Zeiss - Published At: 2016-08-20 14:56 - (71 Reads)
In this study the EPICA Dome C (Antarctica) ice core has been used to measure a high resolution record of atmospheric CO2 and methane concentrations over the last deglaciation about 19,000 to 11,000 years ago. Comparing the CO2 record to the Antarctic surface air temperature reveals a close correlation, but the resolution of the record is not sufficient to determine whether there is a lag between temperature and CO2. However, the times at which temperature and CO2 began to rise can be distinguished. The ice core record revealed that start of the CO2 increase lagged rising temperature by about 800 years. An uncertainty analysis suggests that the lag could have been as low as 200 or as much as 1400 years. This result is consistent with the Southern Hemisphere playing a dominant role in the rise in atmospheric CO2. Methane was found to increase at about the same time as CO2, but the rise in methane is thought to have been determined by Northern Hemisphere processes. Atmospheric CO2 Concentrations over the Last Glacial Termination, Eric Monnin et al., Science 05 Jan 2001: Vol. 291, Issue 5501, pp. 112-114

CO2 drove, but did not trigger, warming during last deglaciation

Author: Geoff Zeiss - Published At: 2016-08-15 17:06 - (87 Reads)
Climate
In this study global and regional surface temperatures during the last deglaciation have been reconstructed from proxy temperature records from 80 geographically distributed sites. Comparison with the atmospheric CO2 record reveals that atmospheric CO2 is closely correlated with global surface temperature, but the increase in global surface temperature lagged atmospheric CO2 throughout the last deglaciation. It is suggested that rising CO2 amplified the global warming trend. To investigate regional effects separate temperature reconstructions were developed for the Northern and Southern Hemispheres. It was found that in the Southern Hemisphere the rise in temperature preceded rising CO2, consistent with Antarctic ice-core results, whereas in the Northern Hemisphere temperature lagged CO2. Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation, Jeremy D. Shakun et al, Nature, 484, 49–54 (05 April 2012) doi:10.1038/nature10915

Southern Ocean warming preceded rising CO2 during the last deglaciation

Author: Geoff Zeiss - Published At: 2016-08-13 16:19 - (125 Reads)
Climate
This important article provides evidence that southern ocean warming pre-dated the rise of atmospheric CO2. Radiocarbon dating of micro organisms living on the deep ocean floor and in surface waters in a marine core collected in the western tropical Pacific was used to determine the relative chronology of warming in the southern ocean near Antarctica and rising CO2 during the last deglaciation. The results provide evidence that that the southern ocean off Antarctica warmed by ~2°C between 19,000 and 17,000 years before the present, about 1,000 years before the rise in atmospheric CO2. Southern Hemisphere and Deep-Sea Warming Led Deglacial Atmospheric CO2 Rise and Tropical Warming, Lowell Stott, Axel Timmermann, Robert Thunell, Science 19 Oct 2007:Vol. 318, Issue 5849, pp. 435-438 DOI: 10.1126/science.1143791

Accounting for global and regional warming during the last deglaciation

Author: Geoff Zeiss - Published At: 2016-08-09 17:40 - (120 Reads)
Climate
The last deglacial warming, which stretched from 19 thousand to 11 thousand years ago, was characterized by increases in surface temperatures of 10-15 °C, sea level rise of 80 meters and by increased atmospheric greenhouse gas concentrations. In this study the authors compiled and analyzed sea surface temperatures and precipitation from ice cores, sea floor sediments, pollen, cave calcite records, and sea phytoplankton records. A principal component analysis revealed two important trends responsible for the variability in temperature during this transition. The dominant warming trend started at about the time of increasing Northern Hemisphere summer insolation. This trend, which ultimately brought temperatures to pre-industrial levels, correlates strongly with increasing greenhouse gas levels. The second trend the analysis revealed is responsible for the pronounced millennial-scale variability such as the Oldest Dryas cooling, Younger Dryas cooling and intervening Bølling-Allerød warming period. Evidence from ocean sediments suggest this trend is associated with changes in the strength of the primary Atlantic north/south current. Global climate evolution during the last deglaciation, Peter U. Clark, Jeremy D. Shakun, et al., Proceedings of the National Academy of Sciences 2012 vol. 109 no. 19 E1134–E1142

New evidence affirms interglacial warming linked to small variations in Earth's orbit

Author: Geoff Zeiss - Published At: 2016-08-03 18:04 - (487 Reads)
Climate
Approximately 800,000 years ago, something changed within the climate system that led to glacial/interglacial periods with a cycle time of roughly 100,000 years. In 1941, Milutin Milankovitch introduced his orbital forcing theory which hypothesized that this cycle could be linked to variations in incoming solar radiation resulting from small, predictable changes in the Earth's orbit about the sun. In 1976 an analysis of deep sea sediment cores provided the first evidence supporting this theory. However, an influential study of calcite cores from Devils Hole in 1992 concluded that the evidence did not support the theory. In this study the original calcite cores from Devils Hole were reexamined and new cores analyzed. A systematic correction was identified that is required in dating calcite cores in Devils Hole and with this correction the calcite chronology does support the theory, thus vindicating the orbital forcing hypothesis. Reconciliation of the Devils Hole climate record with orbital forcing, Gina E. Moseley, R. Lawrence Edwards, Kathleen A. Wendt, Hai Cheng, Yuri Dublyansky, Yanbin Lu, Ronny Boch, Christoph Spötl, Science 08 Jan 2016: Vol. 351, Issue 6269, pp. 165-168 DOI: 10.1126/science.aad4132



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