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~~DISCUSSION:closed|Discussion on core experiment greenhouse gases~~

====== Last Deglaciation Greenhouse Gases ======

<note info>\\ Contacts: [[R.Ivanovic@leeds.ac.uk|Ruža Ivanović]], [[L.J.Gregoire@leeds.ac.uk|Lauren Gregoire]], [[Didier.Roche@lsce.ipsl.fr|Didier Roche]]</note>

[[pmip3:wg:degla:bc:core|Go back]] to the main core experiment design page. \\
[[pmip3:wg:degla:index|Go back]] to the main working group page. \\
\\ 
Please use the //Discussion// section below to specifically comment on the choice of __greenhouse gases__ for the core experiment. \\
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===== Carbon Dioxide =====

The composite record (EPICA Dome C, Vostok and Taylor Dome) from [[http://www.nature.com/nature/journal/v453/n7193/full/nature06949.html | Lüthi et al. (2008)]]<sup>[1]</sup> provides CO<sub>2</sub> data spanning 800 ka to present. 
The data will be provided on the AICC2012 timescale of [[http://www.clim-past.net/9/1733/2013/cp-9-1733-2013.html | Veres et al. (2013)]]<sup>[2]</sup>. \\
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**Comparison of CO2 records and the PMIP3 LGM:** ((Plot produced by Lauren Gregoire, Feb 2015)) \\
{{ http://homepages.see.leeds.ac.uk/~earri/pmip_deglac/CO2_comparison.png? | Comparison of CO2 }} 
In particular, note how the new AICC2012<sup>[2]</sup> age model affects the timing of the record and the 'LGM' (21 ka; vertical dashed line) CO<sub>2</sub> value; now 188 ppm compared to 185 ppm in PMIP3. There are also differences in timing and in the LGM value compared to the higher resolution [[http://www.nature.com/nature/journal/v514/n7524/full/nature13799.html | Marcott et al. (2014)]]<sup>[3]</sup> record.\\
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We are proposing to use the composite record of [[http://www.nature.com/nature/journal/v453/n7193/full/nature06949.html | Lüthi et al. (2008)]]<sup>[1]</sup>; as per the magenta and red lines. \\

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===== Methane =====

The EPICA Dome C record from [[http://www.nature.com/nature/journal/v453/n7193/full/nature06950.html | Loulergue et al. (2008)]]<sup>[4]</sup> provides CH<sub>4</sub> data also spanning 800 ka to present.
The data will be provided on the AICC2012 timescale of [[http://www.clim-past.net/9/1733/2013/cp-9-1733-2013.html | Veres et al. (2013)]]<sup>[2]</sup>. \\
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**EPICA Dome C and the PMIP3 LGM** ((Plot produced by Lauren Gregoire, April 2015)) \\
{{ :pmip3:wg:degla:bc:ch4.png | EPICA Dome C CH4 }} \\
Also note how the new AICC2012<sup>[2]</sup> age model affects the 'LGM' (21 ka; vertical dashed line) CH<sub>4</sub> value.\\

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===== Nitrous Oxide =====

The TALDICE record from [[http://www.sciencedirect.com/science/article/pii/S0012821X10006023 | Schilt et al. (2010)]]<sup>[5]</sup> provides N<sub>2</sub>O data spanning 140 ka to present.
The data will be provided on the AICC2012 timescale of [[http://www.clim-past.net/9/1733/2013/cp-9-1733-2013.html | Veres et al. (2013)]]<sup>[2]</sup>.\\
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**TALDICE and the PMIP3 LGM** ((Plot produced by Lauren Gregoire, Feb 2015)) \\
{{ http://homepages.see.leeds.ac.uk/~earri/pmip_deglac/N2O.png? | TALDICE N2O }} \\
The old PMIP3 'LGM' (21 ka; vertical dashed line) CH<sub>4</sub> value, probably remains representative of the glacial period for the model spin-up, although the 21 ka value for the transient run will be lower, as per the record above. \\

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===== Points to discuss =====

Please think about the following points and add any comments on these or any other aspects of the experiment design to the discussion section below: [Topics will be added here as they are raised below or by email.]
  * **RESOLVED** With the new AICC2012<sup>[2]</sup> age model, the LGM values for CO<sub>2</sub><sup>[1]</sup> and CH<sub>4</sub><sup>[4]</sup> are inaccurate, as can be seen from the plots above. Do we need a new PMIP LGM definition for these greenhouse gases in accordance with the records? **DECISION (Oct 2015): We have used the new, up to date CO<sub>2</sub> (188 ppm) and CH<sub>4</sub> (375 ppb) values for our LGM equilibrium-type 21 ka spinup. We do not know what the LGM group's decision will be.**\\ \\
  * **RESOLVED** N<sub>2</sub>O<sup>[1]</sup> values take a dive in the lead up to 21 ka. The PMIP3 value of 200 ppb looks fairly representative of the LGM state, even though this is a bit higher than the actual 21 ka value. We recommend that groups spin-up with 200 ppb N<sub>2</sub>O, and begin the transient simulation from 21 ka in the record (as shown in the plot above). **DECISION (Oct 2015): We have stuck with the old, more representative N<sub>2</sub>O value of 200 ppb. However, the transient 'spinup' 26-21 ka and the transient run (21-9 ka) should use the chronologically accurate values, as plotted above. We do not know what the LGM group's decision will be.** \\ \\
  * **RESOLVED** Should the core experiment use the [[http://www.nature.com/nature/journal/v514/n7524/full/nature13799.html | Marcott et al. (2014)]]<sup>[3]</sup> CO<sub>2</sub> records? \\ For example, these newer data are higher resolution than [[http://www.nature.com/nature/journal/v453/n7193/full/nature06949.html | Lüthi et al. (2008)]]<sup>[1]</sup>, but are restricted to 23-9 ka. Therefore more consistency may be be gained from using the older [[http://www.nature.com/nature/journal/v453/n7193/full/nature06949.html | Lüthi et al. (2008)]]<sup>[1]</sup> CO<sub>2</sub> records, if longer simulations are planned by groups. Also, CH<sub>4</sub> and N<sub>2</sub>O data are not yet available in such high resolution. **DECISION (Oct 2015): We have chosen to use the older data from [[http://www.nature.com/nature/journal/v453/n7193/full/nature06949.html | Lüthi et al. (2008)]]<sup>[1]</sup>.** \\ \\

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=====References=====
  - Lüthi, D. et al. High-resolution carbon dioxide concentration record 650,000–800,000 years before present. Nature 453, 379–382 (2008).
  - Veres, D. et al. The Antarctic ice core chronology (AICC2012): an optimized multi-parameter and multi-site dating approach for the last 120 thousand years. Clim Past 9, 1733–1748 (2013). 10, 297–317 (1991). 
  - Marcott, S. A. et al. Centennial-scale changes in the global carbon cycle during the last deglaciation. Nature 514, 616–619 (2014).
  - Loulergue, L. et al. Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years. Nature 453, 383–386 (2008).
  - Schilt, A. et al. Atmospheric nitrous oxide during the last 140,000 years. Earth Planet. Sci. Lett. 300, 33–43 (2010).\\ \\

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