Research ArticleENVIRONMENTAL STUDIES

An observation-constrained assessment of the climate sensitivity and future trajectories of wetland methane emissions

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Science Advances  10 Apr 2020:
Vol. 6, no. 15, eaay4444
DOI: 10.1126/sciadv.aay4444
  • Fig. 1 Response of wetland CH4 emissions to climate variables.

    Median value of the normalized emission En as function of the precipitation P and the temperature T is shown for the five climate zones (A to E) and at global scale (F). Emissions are derived from MACC project over 2000–2012 (MACC_NOAA INV). Precipitation P and temperature T are from the CRU database. The map of climate zones and the relevant mean value of wetland CH4 flux (Fm), together with the wetland area (Aw), are displayed. The sizes of the temperature Tc and precipitation Pc bins are set to 1°C and 1 cm/month, respectively.

  • Fig. 2 Sensitivity of wetland CH4 emissions to temperature T and precipitiation P for the five climate zones and at global scale.

    The emissions are derived from both atmospheric inversions (INVs) and LSM simulations. T and P data are from CRU database. The sensitivity of the emissions to T (SET; A, B) and to P (SEP; E, F) are shown. Results for the intrinsic (ISET and ISEP; A, E) and for the apparent (ASET and ASEP; B, F) sensitivities are shown, respectively. For ASET and ASEP, the covariance between climate drivers was estimated using the 3-monthly average slopes between P and T. The Whisker plots shown at the bottom of each sensitivity matrix graph (C, D, G, H) are computed from the ensemble of all the inversions (black) and for all the LSMs (green). The whisker plots show the minimum and maximum SET or SEP values (bars), and the 25th and 75th percentiles (boxes). The median values are shown by horizontal line in the box. The values of SET and SEP obtained from the MACC_NOAA INV estimates the reference inversion in this study) are shown by open circles.

  • Fig. 3 Projected trajectories of wetland CH4 emissions.

    Simulations of wetland CH4 emissions using the observation-driven model and climate projections of an ensemble of CMIP5 models for the scenarios RCP2.6 (top) and RCP8.5 (middle). Two versions of the observation-driven model are considered: simulations without any adaptation of the wetland to the new climate (no adaptation; red) and simulations with full adaptation to climate (adaptation; green). Results are compared to those of Zhang et al. (19) (gray). The observation-driven model estimates are scaled up by the ratio between the projected wetland areas and the computed areas in year 2000 based on Zhang et al. (19) simulations. Envelopes in the top and middle panels are enclosed by 25th and 75th percentiles of the ensemble predictions. Solid lines are the median values. The bottom graph shows the yearly variations of the computed wetland areas from Zhang et al. (19) from the ensemble of CMIP5 climate models. The number of models used for each RCP is shown in the bottom graph. The observation-driven method uses for wetland methane emissions the MACC_NOAA INV.

  • Fig. 4 Wetland CH4 emissions obtained by combining the observation-driven model, wetland areas from Zhang et al. (19) and projections of an ensemble of CMIP5 climate models for the four scenarios (RCP 2.6, RCP4.5, RCP6.0, and RCP8.5) based on MACC inversion and assuming no adaptation to climate.

    Black lines (violet for GISS-E2-R) in the top panel of each scenario (A, B, E, F) indicate global emissions computed with individual CMIP5 model outputs; the red line indicates the median of the ensemble. The bottom panels (C, D, G, H) show a time series of the percentage contribution from each climate zone.

Supplementary Materials

  • Supplementary Materials

    An observation-constrained assessment of the climate sensitivity and future trajectories of wetland methane emissions

    Ernest N. Koffi, Peter Bergamaschi, Romain Alkama, Alessandro Cescatti

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