Continuous records of the atmospheric greenhouse gases CO2, CH4, and N2O and their radiative forcing since the penultimate glacial maximum

• Main Authors: Köhler, Peter, Nehrbass-Ahles, Christoph, Schmitt, Jochen, Stocker, T. F., Fischer, Hubertus
• Format: Conference Object
• Language: unknown
• Published: 2017
• Subjects: ice core
• Online Access: https://epic.awi.de/id/eprint/44527/; https://epic.awi.de/id/eprint/44527/1/poster_ghg_pages2017_zaragossa.pdf; https://hdl.handle.net/10013/epic.50839; https://hdl.handle.net/10013/epic.50839.d001

Continuous records of the atmospheric greenhouse gases (GHG) CO2, CH4, and N2O are necessary input data for transient climate simulations and their related radiative forcing important components in analyses of climate sensitivity and feedbacks. Since the available data from ice cores are discontinuous and partly ambiguious a well-documented decision process during data compilation followed by some interpolating post- processing are necessary to obtain those desired time series. Here we document our best-guess data compilation of published ice core records and recent measurements on firn air and atmospheric samples covering the period from the penultimate glacial maximum (∼156 kyr BP) to 2016 CE. A smoothing spline method is applied to translate the discrete and irregularly spaced data points in continuous time series. These splines are assumed to represent the evolution of the atmospheric mixing ratios for the three GHGs. Global-mean radiative forcing for each GHG is computed using well-established, simple formulations. Newest published age scales are used for the ice core data. While CO2 is representing an integrated global signal, we compile only a southern hemisphere record of CH4 and identify how much larger a northern hemisphere or global CH4 record might have been due to its interhemispheric gradient. Data resolution and uncertainties are considered in the spline procedure and typical cutoff periods, defining the degree of smoothing, range from 5000 years for the less resolved older parts of the records to 4 years for the densely- sampled recent years. The data sets describe seamlessly the GHG evolution on orbital and millennial time scales for glacial and glacial-interglacial variations and on centennial and decadal time scales for the anthropogenic period.