Research ArticleCLIMATOLOGY

Large regional shortwave forcing by anthropogenic methane informed by Jovian observations

See allHide authors and affiliations

Science Advances  26 Sep 2018:
Vol. 4, no. 9, eaas9593
DOI: 10.1126/sciadv.aas9593
  • Fig. 1 Difference in CH4 optical depths between RTMIP experiments 3b and 3d.

    Green line: Optical depth differences from HITRAN 2012; orange and red lines: optical depth differences computed using the Jovian empirical spectra added to the HITRAN 2012 results for wave numbers below and above 12,000 cm−1, respectively (see Materials and Methods).

  • Fig. 2 Monthly mean global direct, instantaneous, unadjusted shortwave radiative forcing at the tropopause from changing tropospheric concentrations of CH4 from 806 to 1760 ppbv.

    Solid lines show the mean forcing for each month averaged over 2006 to 2010 CE. Blue and green (red and orange) bands show the range of monthly forcing under all-sky (clear-sky) aerosol-free tropospheric conditions for each individual year using atmospheric state information from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Mk3-6-0 (56) and INMCM4 (55) Earth System Models (ESMs), respectively (see Materials and Methods).

  • Fig. 3 Annual mean CH4 shortwave forcings and near-infrared reflected fluxes from the CSIRO Mk3-6-0 (56) ESM.

    (A) CH4 direct, instantaneous, unadjusted shortwave forcing at the tropopause under all-sky, aerosol-free tropospheric conditions. (B) Top-of-atmosphere (TOA) near–infrared (IR) reflected flux under clear-sky, aerosol-free conditions. (C) Area-weighted cumulative probability distribution of all-sky CH44 forcing. Dotted lines denote the point where the forcing exceeds 0, dashed lines denote where the forcing equals the annual mean global all-sky forcing (Table 2), and the circle and cross (plus) symbols and labels denote the mean (maximum) forcing value.

  • Fig. 4 Annual mean enhancements to CH4 shortwave forcings and reflected fluxes by clouds from the CSIRO Mk3-6-0 (56) ESM.

    (A) Difference in CH4 forcing at the tropopause between all-sky and clear-sky aerosol-free tropospheric conditions. (B) TOA near-infrared cloud radiative effect. (C) Area-weighted cumulative probability distribution of cloud-radiative enhancements. Dotted lines denote the point where the forcing exceeds 0, dashed lines denote where the forcing equals the annual mean global all-sky forcing (Table 2), and the circle and cross (plus) symbols and labels denote the mean (maximum) forcing value.

  • Table 1 Direct, instantaneous, unadjusted shortwave radiative forcing by methane (in W/m2) at three atmospheric levels under RTMIP experimental protocol (2).

    Column-labeled RTMIP shows original RTMIP results (2); columns labeled 2000, 2004, 2008, 2012, and Jovian+2012 show forcings computed using the HITRAN 2000 (21), 2004 (30), 2008 (22), and 2012 (10) databases out to 12,000 cm−1 (see Materials and Methods), and the Jovian empirical methane parameterization including parametric uncertainty (2-σ, in parentheses) (9) combined with HITRAN 2012 out to 25,000 cm−1 (see Materials and Methods). Rows with units in the Δ column give the differences in forcings relative to the HITRAN 2000 values in absolute and percentage units.

    LevelΔRTMIP2000200420082012Jovian+2012
    TOA+0.09+0.096+0.098+0.097+0.098+0.099 ± (0.0)
    W/m2+0.002+0.002+0.002+0.003
    %+2.064+1.738+2.510+3.349
    Tropopause−0.13−0.127−0.132−0.132−0.132−0.132 ± (2.6 × 10−8)
    W/m2−0.005−0.005−0.005−0.005
    %+4.211+3.927+3.978+3.636
    Surface−0.55−0.574−0.589−0.588−0.590−0.594 ± (1.6 × 10−8)
    W/m2−0.015−0.014−0.017−0.020
    %+2.673+2.452+2.889+3.495
  • Table 2 Direct, instantaneous, unadjusted annual mean global shortwave methane radiative forcing at the tropopause under all-sky and clear-sky conditions using atmospheric state information from the CSIRO Mk3-6-0 (56) and INMCM4 (55) ESMs averaged over 2006 to 2010 CE (see Materials and Methods).

    Uncertainties denote the interannual variability in these forcings.

    ConditionModelAnnual mean forcing (W/m2)
    All-skyCSIRO Mk3-6-00.025 ± (1 × 10−4)
    INMCM40.026 ± (4 × 10−4)
    Clear-skyCSIRO Mk3-6-00.011 ± (3 × 10−5)
    INMCM40.008 ± (2 × 10−4)

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/9/eaas9593/DC1

    Fig. S1. Time evolution of CH4 spectroscopic properties catalogued in the HITRAN databases.

    Fig. S2. Change in column-integrated CH4 optical depth between RTMIP experiments 3b (2000 CE conditions) and 3d (1860 CE conditions) using the HITRAN 2000 line database.

    Fig. S3. Perturbations to changes in column-integrated CH4 optical depth between RTMIP experiments 3b and 3d.

    Fig. S4. Cumulative perturbations to changes in CH4 direct, instantaneous, unadjusted spectral forcing between RTMIP experiments 3b and 3d due to substituting the HITRAN 2004, 2008, and 2012 line databases for the HITRAN 2000 line database.

    Fig. S5. Near-infrared black-sky surface albedo retrieved from MODIS for 2003 to 2014 CE.

    Table S1. The variable names, source model components, and descriptive names of the monthly mean fields used as input to the OSSE from the CMIP.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Time evolution of CH4 spectroscopic properties catalogued in the HITRAN databases.
    • Fig. S2. Change in column-integrated CH4 optical depth between RTMIP experiments 3b (2000 CE conditions) and 3d (1860 CE conditions) using the HITRAN 2000 line database.
    • Fig. S3. Perturbations to changes in column-integrated CH4 optical depth between RTMIP experiments 3b and 3d.
    • Fig. S4. Cumulative perturbations to changes in CH4 direct, instantaneous, unadjusted spectral forcing between RTMIP experiments 3b and 3d due to substituting the HITRAN 2004, 2008, and 2012 line databases for the HITRAN 2000 line database.
    • Fig. S5. Near-infrared black-sky surface albedo retrieved from MODIS for 2003 to 2014 CE.
    • Table S1. The variable names, source model components, and descriptive names of the monthly mean fields used as input to the OSSE from the CMIP.

    Download PDF

    Files in this Data Supplement:

Navigate This Article