Historical GHG concentrations CMIP6 Forcings: Historical GHG concentrations A collaboration between David Etheridge, Paul Fraser, Pep Cannadell, (CSIRO)… Katja Dommenget, Alexander Nauels, Elisabeth Vogel, Malte Meinshausen (Climate & Energy College, University of Melbourne), … and many others. Malte Meinshausen, 19th October 2015 Australian-German Climate & Energy College, The University of Melbourne, Australia, malte.Meinshausen@unimelb.edu.au

The Dataset CMIP6 Historical GHG concentrations Time-span: (With optional backward extension to year 1000 for CO2, CH4 and N2O) Gases: CO2, CH4, N2O, C2F6, CF4, HFC-125, HFC-134a, HFC-143a, HFC-23, SF6, NF3, and 16 ODS, namely: CFC-11, CFC-12, CFC-113, CFC-114, CFC-115, CCl14, CH3CCl3, HCFC-22, HCFC-141b, HCFC-142b, Halon1211, Halon1202, Halon1301, Halon2404, CH3Br, CH3Cl Time resolution Annual averages. Value for 1850 is average mixing ratio from 1st Jan 1850 to 31 Dec 1850 (with optional extension to monthly values for CO2 and CH4). Spatial resolution: Global averages and hemispheric means.

Law Dome record: Rubino et al. 2013, MacFarling et al Law Dome record: Rubino et al. 2013, MacFarling et al. 2006; Etheridge et al. 1996; Ehteridge et al. 1998

Law Dome record: Rubino et al. 2013, MacFarling et al Law Dome record: Rubino et al. 2013, MacFarling et al. 2006; Etheridge et al. 1996; Ehteridge et al. 1998

Law Dome record: Rubino et al. 2013, MacFarling et al Law Dome record: Rubino et al. 2013, MacFarling et al. 2006; Etheridge et al. 1996; Ehteridge et al. 1998

Law Dome record: Rubino et al. 2013, MacFarling et al Law Dome record: Rubino et al. 2013, MacFarling et al. 2006; Etheridge et al. 1996; Ehteridge et al. 1998

CO2 Mixing Ratio (ppm) Data: NOAA ESLR - CO2 and CH4 semidiurnal flask values from1968 - 2015 and 1983 – 2015, ~105 stations (~ 1/3 SH and 2/3 NH), own interpolation.

CH4 Data: NOAA ESLR - CO2 and CH4 semidiurnal flask values from1968 - 2015 and 1983 – 2015, ~105 stations (~ 1/3 SH and 2/3 NH), own interpolation.

CH4 Data: NOAA ESLR - CO2 and CH4 semidiurnal flask values from1968 - 2015 and 1983 – 2015, ~105 stations (~ 1/3 SH and 2/3 NH), own interpolation.

N2O Data: NOAA ESLR - N2O monthly mean flask values from 1977 – 2015, 13 stations (9 NH and 4 SH), globally and hemispherically averaged data available, own interpolation.

Hemispheric Concentrations Important to get CMIP6 historical hemispheric / latitudinal forcing correct – for detection & attribution, for estimating climate sensitivity & TCR, for atmospheric chemistry etc. CO2, CH4, N2O and short-lived forcers in particular have north-south gradient. Higher northern hemisphere GHG forcing slightly offsets higher northern hemispheric aerosol cooling. Problem: We have latitudinally resolved observations only from about 1980s. Before the 80s: For methane and N2O, there is Greenland firn data (NEEM) and Antarctic ice (Law Dome) records. Regressing the NH-SH difference against NH-SH emission difference could allow backcasting historical hemispheric GHG concentrations.  Complete NH, SH, and global average concentrations over period 1850 to 2014

For Discussion Why not produce historical GHG concentrations with monthly resolution to capture seasonal cycle or higher latitudinal resolution? Not sufficient basis for pre-1980 Difficult to model sensibly for future scenarios. How to produce consistent GHG concentration timeseries of future scenarios for concentration-driven models? How to implement hemispheric GHG concentrations in CMIP6 models? (Would a latitudinal, even if only approximate, interpolation be easier or done anyway within CMIP6 models?)

Complete hermispheric Data series Scheduled for 1 January 2016. Thank you.

Data This exercise is going to build on a wide array of data from the community and any suggestions for additional data are much appreciated. Shown Data: Rubino, Mauro; Etheridge, David; Trudinger, Cathy; Allison, Colin; Battle, Mark; Langenfelds, Ray; et al. A revised 1000 year atmospheric d13C-CO2 record from Law Dome and South Pole, Antarctica. Journal of Geophysical Research- Atmospheres. 2013; 118(5):8482-8499. MacFarling Meure, C. M.; Etheridge, D. M.; Trudinger, C. M.; Steele, L. P.; Langenfelds, R. L.; van Ommen, T. D.; et al. Law Dome CO2, CH4 and N2O ice core records extended to 2000 years BP. Geophysical research letters. 2006; 33:L14810, doi:10.1029/2006GL026152. Etheridge, D. M.; Steele, L. P.; Langenfelds, R. L.; Francey, R. J.; Barnola, J. -M.; Morgan, V. I. Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn. Journal of geophysical research - Atmospheres. 1996; 101(D2):4115-4128. Etheridge, D. M.; Steele, L. P.; Francey, R. J.; Langenfelds, R. L. Atmospheric methane between 1000 A.D. and present: evidence of anthropogenic emissions and climatic variability. Journal of geophysical research - Atmospheres. 1998; 103(D13):15979-15993. NOAA ESRL - CO2 and CH4 semidiurnal flask values from1968 - 2015 and 1983 – 2015, ~105 stations (~ 1/3 SH and 2/3 NH), http://www.esrl.noaa.gov/gmd/ccgg/about/global_means.html N2O monthly mean flask values from 1977 – 2015, 13 stations (9 NH and 4 SH), globally and hemispherically averaged data available, http://www.esrl.noaa.gov/gmd/hats/combined/N2O.html NEEM-2011-S1 Ice Core 1800 Year Continuous Methane Dat. World Data Center for Paleoclimatology, Boulder, and NOAA Paleoclimatology Program, original_Source_URL: ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/neem/neem2011s1-ch4.txt Methods: Linear interpolation Method (in space and time) : optionally Thoning et al. (1989), Tans et al. (1989) for final dataset