[font face=Serif][font size=5]New timeline links volcanic eruptions to centuries of cold temperature extremes[/font]

By Jim Shelton
July 8, 2015

[font size=3]A new study reorders the timing and reveals the climate impact of nearly 300 major volcanic eruptions worldwide, dating back to the early Roman period.

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The study found that 15 of the 16 coldest summers recorded between 500 B.C. and A.D. 1,000 followed large volcanic eruptions. Previous ice-core timelines were off by five to 10 years in the first millennium A.D., with discrepancies beginning to accumulate from the mid-1200s. This prevented scientists from connecting volcanic eruptions with many major human events such as famine and plague.

“Using new records we are able to show that large volcanic eruptions in the tropics and high latitudes were the dominant drivers of climate variability, responsible for numerous and widespread summer cooling extremes over the past 2,500 years,” said lead author Michael Sigl, assistant research professor at DRI and a postdoctoral fellow with the Paul Scherrer Institute in Switzerland.

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Ludlow said the new timeline helps resolve the origin of one of the most dramatic climatic downturns in recent human history: A period of unusually cold summers from A.D. 536-550 in the Northern Hemisphere that likely contributed to crop failures, famines, and plague.

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[font face=Serif][font size=5]Volcanic eruptions slow down climate change -- temporarily[/font]

[font size=4]Volcanic aerosols have acted during the last 10 years as a natural umbrella to slow down global temperature increase from greenhouse gases[/font]

Karlsruher Institut für Technologie (KIT)

[font size=3]Although global concentration of greenhouse gases in the atmosphere has continuously increased over the past decade, the mean global surface temperature has not followed the same path. A team of international reseachers, KIT scientists among them, have now found an explanation for this slowing down in global warming: the incoming solar radiation in the years 2008-2011 was twice as much reflected by volcanic aerosol particles in the lowest part of the stratosphere than previously thought. The team presents their study in Nature Communications (DOI: 10.1038/ncomms8692).

For the lowest part of the stratosphere - i. e. the layer between 10 and 16 kilometres - little information was available so far, but now the international IAGOS-CARIBIC climate project combined with satellite observations from the CALIPSO lidar provided new essential information. According to the study, the cooling effect due to volcanic eruptions was clearly underestimated by climate models used for the last Intergovernmental Panel on Climate Change (IPCC) report. Led by the University of Lund, Sweden, and supported by the NASA Langley Research Center, USA, and the Royal Netherlands Meteorological Institute, three major German atmospheric research institutes were also involved: the Max Planck Institute for Chemistry in Mainz (MPI-C), the Leibniz Institute for Tropospheric Research in Leipzig (TROPOS) and the Karlsruhe Institute of Technology (KIT). Since more frequent volcanic eruptions and the subsequent cooling effect are only temporary the rise of Earths' temperature will speed up again. The reason is the still continuously increasing greenhouse gas concentration, the scientists say.

In the first decade of the 21st century the average surface temperature over the northern mid-latitude continents did increase only slightly. This effect can be now explained by the new study on volcanic aerosol particles in the atmosphere reported here. The study uses data from the tropopause region up to 35 km altitude, where the former is found between 8 km (poles) and 17 km (equator) altitude. The tropopause region is a transition layer between the underlying wet weather layer with its clouds (troposphere) and the dry and cloud-free layer above (stratosphere). „Overall our results emphasize that even smaller volcanic eruptions are more important for the Earth´s climate than expected", summarize CARIBIC coordinators Dr. Carl Brenninkmeijer, MPI-C, and Dr. Andreas Zahn, KIT. The IAGOS-CARIBIC observatory was coordinated and operated by the MPI-C until the end of 2014, since then by the KIT.

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