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Ice-core dating corroborates tree ring chronologies

Filed under: — group @ 5 August 2015

Guest commentary from Jonny McAneney

You heard it here first

Back in February, we wrote a post suggesting that Greenland ice cores may have been incorrectly dated in prior to AD 1000. This was based on research by Baillie and McAneney (2015) which compared the spacing between frost ring events (physical scarring of living growth rings by prolonged sub-zero temperatures) in the bristlecone pine tree ring chronology, and spacing between prominent acids in a suite of ice cores from both Greenland and Antarctica. The main conclusion was that ice core dates, in particular those ice cores relied upon the Greenland Ice Core Chronology 2005 (GICC05), such as the NEEM S1 core, were too old by approximately seven years during the 6th and 7th centuries AD.

Last month, in an excellent piece of research (Sigl et al., 2015) by a collaboration including Earth scientists, dendrochonologists, and historians, the chronology of the Greenland North Eemian Ice Drilling core (NEEM) has been reassessed and re-dated, confirming that such an offset does indeed exist in the GICC05 timescale below AD 1000. The clinching evidence was provided by linking tree-ring chronologies to ice cores through two extraterrestrial events…
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  1. M.G.L. Baillie, and J. McAneney, "Tree ring effects and ice core acidities clarify the volcanic record of the first millennium", Climate of the Past, vol. 11, pp. 105-114, 2015.
  2. B.M. Vinther, H.B. Clausen, S.J. Johnsen, S.O. Rasmussen, K.K. Andersen, S.L. Buchardt, D. Dahl-Jensen, I.K. Seierstad, M. Siggaard-Andersen, J.P. Steffensen, A. Svensson, J. Olsen, and J. Heinemeier, "A synchronized dating of three Greenland ice cores throughout the Holocene", J. Geophys. Res., vol. 111, 2006.
  3. M. Sigl, J.R. McConnell, L. Layman, O. Maselli, K. McGwire, D. Pasteris, D. Dahl-Jensen, J.P. Steffensen, B. Vinther, R. Edwards, R. Mulvaney, and S. Kipfstuhl, "A new bipolar ice core record of volcanism from WAIS Divide and NEEM and implications for climate forcing of the last 2000 years", Journal of Geophysical Research: Atmospheres, vol. 118, pp. 1151-1169, 2013.
  4. M. Sigl, M. Winstrup, J.R. McConnell, K.C. Welten, G. Plunkett, F. Ludlow, U. Büntgen, M. Caffee, N. Chellman, D. Dahl-Jensen, H. Fischer, S. Kipfstuhl, C. Kostick, O.J. Maselli, F. Mekhaldi, R. Mulvaney, R. Muscheler, D.R. Pasteris, J.R. Pilcher, M. Salzer, S. Schüpbach, J.P. Steffensen, B.M. Vinther, and T.E. Woodruff, "Timing and climate forcing of volcanic eruptions for the past 2,500 years", Nature, vol. 523, pp. 543-549, 2015.

Unforced variations: Aug 2015

Filed under: — group @ 3 August 2015

This month’s open thread. A traditional time to discuss the Arctic sea ice minimum. But NH summer heatwaves, and to be fair, snow in the southern hemisphere, are also fair game…

Unforced variations: July 2015

Filed under: — group @ 3 July 2015

This month’s open thread. How about a focus on cimate science this time? Data visualizations anyone?

Heaven belongs to us all – the new papal encyclical

Filed under: — stefan @ 18 June 2015

Guest post by Brigitte Knopf

With his encyclical “Laudato Si” the Pope has written more than a moral appeal without obligation. He has presented a pioneering political analysis with great explosive power, which will probably determine the public debate on climate change, poverty and inequality for years to come. Thus, the encyclical is also highly relevant to me as a non-Catholic and non-believer; the implications of the encyclical are very apparent through the eyes of a secular person.

The core of the encyclical makes clear that global warming is a “global problem with grave implications: environmental, social, economic, political and for the distribution of goods” (25 – where the numbers refer to the numbering in the encyclical). The reasons identified are mainly the current models of production and consumption (26). The encyclical emphasizes that the gravest effects of climate change and the increasing inequality are suffered by the poorest (48). Since we face a complex socio-ecological crisis, strategies for a solution demand an integrated approach to combating poverty (139). So far, however, governments have not found a solution for the over-exploitation of the global commons, such as atmosphere, oceans, and forests (169). Therefore, the encyclical focusses on actors, such as non-governmental organizations, cooperatives and intermediate groups (179) and calls for a dialogue between politics, science, business and religion.

The encyclical is, with 246 individual points, too extensive to be discussed in here in its entirety, but three aspects are particularly noteworthy:

  1. it is based unequivocally onthe scientific consensusthat global warmingis taking placeand that climate changeis man-made; itrejects thedenialof anthropogenicwarming;
  2. it unmasks the political and economic structures of power behind the climate change debate and stresses the importance of non-state actors in achieving change; and
  3. it defines the atmosphere and the environment as a common good rather than a “no man’s land”, available for anyone to pollute. This underlines that climate change is strongly related to the issues of justice and property rights.

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Debate in the noise

Last week there was an international media debate on climate data which appeared to be rather surreal to me. It was claimed that the global temperature data had so far shown a “hiatus” of global warming from 1998-2012, which was now suddenly gone after a data correction. So what happened?

One of the data centers that compile the data on global surface temperatures – NOAA – reported in the journal Science on an update of their data. Some artifacts due to changed measurement methods (especially for sea surface temperatures) were corrected and additional data of previously not included weather stations were added. All data centers are continually working to improve their database and they therefore occasionally present version updates of their global series (NASA data are currently at version 3, the British Hadley Centre data at version 4). There is nothing unusual about this, and the corrections are in the range of a few hundredths of a degree – see Figure 1. This really is just about fine details. More »

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