Anthropogenic forcing dominates global mean sea-level rise since 1970

Transcription

1 Anthropogenic forcing dominates global mean sea-level rise since 1970 Aimée B. A. Slangen 1,2 *, John A. Church 1, Cecile Agosta 3, Xavier Fettweis 3, Ben Marzeion 4 and Kristin Richter 5 1 CSIRO Oceans & Atmosphere, Hobart, Tasmania, Australia 2 Institute for Marine and Atmospheric research Utrecht (IMAU), Utrecht University, Utrecht, The Netherlands 3 Département de Géographie, Université de Liège, Liège, Belgium 4 Institute of Geography, University of Bremen, Bremen, Germany 5 Institute of Atmospheric and Cryospheric Sciences, University of Innsbruck, Innsbruck, Austria * aimee.slangen@gmail.com NATURE CLIMATE CHANGE 1

2 Supplementary Table Table S1: CMIP5 models and experiments used in this study 1. Only the first available realisation is used. Historical Anthropogenic Natural GHG Aerosol (All) only only only only ACCESS 1.3 x - - x - CanESM2 x - x x x CNRM-CM5 x x x x - CSIRO-mk3.6 x x x x x GFDL-CM3 x x x - x GFDL-ESM2M x x x x x GISS-E2-R x x x x x HadGEM2-ES x - x x - IPSL-CM5A-LR x x x x x MR x - x x - MIROC-ESM x - x x - IPSL-CM5A- MIROC-ESM- CHEM x - x x - MRI-CGCM3 x - x x - NorESM1-M x - x x - Total # Models NATURE CLIMATE CHANGE 2

3 SUPPLEMENTARY INFORMATION Supplementary Figures Figure S1: Non-CMIP5 contributions. Contributions that were not explicitly modelled with CMIP5 data are added separately: reservoir impoundment (red solid), groundwater extraction (red dashed) and observed ice sheet dynamics (not shown, ~-4 mm ). Before 1993 the ice sheet dynamical contribution is assumed to be zero. In addition, two corrections are applied to account the natural long-term internal variability causing increased melting in Greenland and in nearby areas, due to a warming that is present in the CRU gridded climate observation data and reanalysis data but not in the CMIP5 model runs. The glacier correction is derived from the difference between the individual CMIP5 glacier contributions and the CRU-driven glacier contribution, which are shown in grey. The glacier contribution before 1950 is corrected using a quadratic fit to the ensemble mean of this difference (black line). After 1960, the difference between the CMIP5 models and the CRU-driven model and the glacier observations 6 is small (ensemble average in blue line, individual models NATURE CLIMATE CHANGE 3 3

4 not shown) and therefore no glacier correction is applied post The Greenland SMB correction for internal variability is derived from the difference between CMIP5-driven results and reanalysis-driven results (difference between 3 reanalyses (ERA-20C, 20CRv2, 20CRv2c) and the CMIP5 ensemble mean in dashed magenta), using a quadratic fit to the ensemble mean difference before 1950 (solid magenta line). The quadratic fits for glaciers and the Greenland contribution were chosen to best match the shape of the differences between CMIP5 models and observationdriven results. However, this has only a small effect on the results, as the difference between a linear and a quadratic fit would amount to no more than a few mm, i.e. less than 1% of the total change over the 20 th century. Both fits are applied before 1950 only. 4 NATURE CLIMATE CHANGE 4

5 SUPPLEMENTARY INFORMATION Figure S2: Derivation of the non-equilibrium constant. For each model we computed the constant that optimises the fit between the historical experiment and the observation average (small red dots, x-axis values, mm yr -1 ). This is plotted against the difference between the steric modelled and observed 7,8 contribution (y-axis, mm). For convenience, the thermosteric anomaly is converted to heat content anomaly using 0.12 ± 0.01 m YJ -1 (right-hand side y-axis, YJ) 9. The least squares fit (red dashed line) shows that for zero difference in the steric contribution a constant of 0.13 mm yr -1 is required (large red dot). This process is repeated for individual observational estimates of GMSLC (small green dots on zerodifference line, individual models not shown for clarity). The uncertainty in the observed steric contribution (blue dashed & blue Gaussian curve) indicates which models are significantly over- or underestimating the steric contribution for NATURE CLIMATE CHANGE 5 5

6 CMIP5 (5 experiments + Control run, Fig 1): Thermal expansion Glaciers incl LIA Ice sheet SMB Figure 2: CMIP5 (5 exp) + Non-CMIP5 Non-CMIP5: Groundwater extrac;on Reservoir storage Ice sheet dynamics Glacier corr (pre-1950) GrSMB corr (pre-1950) Non-equilibrium constant Natural (Fig3a, green): CMIP5 natural experiment: Thermal expansion Glaciers excl LIA Ice sheet SMB Historical (Fig 3b): CMIP5 historical experiment + Non-CMIP5 Anthropogenic (Fig 3c): CMIP5 Anthropogenic experiment: Thermal expansion Glaciers excl LIA Ice sheet SMB Internal variability: CMIP5 Glaciers LIA Glacier corr (pre-1950) GrSMB corr (pre-1950) Non-equilibrium constant Figure S3: Schematic to clarify the terminology used to indicate each of the contributions to GMSLC and to show which contributions are included in each figure in the main text. Contributions can be grouped by CMIP5 (upper left) and non-cmip5 (upper right). An alternative distribution can be made by grouping the contributions according to forcing: Natural (green), Historical (purple), Anthropogenic (red) and Internal variability (light blue). 6 NATURE CLIMATE CHANGE 6

7 SUPPLEMENTARY INFORMATION Figure S4: Explained fractions (%) of total observed sea-level change rates. As in Figure 3 for Church & White, only. NATURE CLIMATE CHANGE 7 7

8 Figure S5: Explained fractions (%) of total observed sea-level change rates. As in Figure 3 for Ray & Douglas only. 8 NATURE CLIMATE CHANGE 8

9 SUPPLEMENTARY INFORMATION Figure S6: Explained fractions (%) of total observed sea-level change rates. As in Figure 3 for Jevrejeva et al., only. NATURE CLIMATE CHANGE 9 9

10 Figure S7: Explained fractions (%) of total observed sea-level change rates. As in Figure 3 for Hay et al., only. 10 NATURE CLIMATE CHANGE 10

11 SUPPLEMENTARY INFORMATION Supplementary References 1. Taylor, K. E., Stouffer, R. J. & Meehl, G. A. An overview of CMIP5 and the experiment design. Bull Am Meteorol Soc 93, (2012). 2. Church, J. A. & White, N. J. Sea-Level Rise from the Late 19th to the Early 21st Century. Surv Geophys (2011). doi: /s Ray, R. D. & Douglas, B. C. Experiments in reconstructing twentieth-century sea levels. Prog. Oceanogr. 91, (2011). 4. Jevrejeva, S., Moore, J. C., Grinsted, A., Matthews, A. P. & Spada, G. Trends and acceleration in global and regional sea levels since Glob. Planet. Change 113, (2014). 5. Hay, C. C., Morrow, E., Kopp, R. E. & Mitrovica, J. X. Probabilistic reanalysis of twentieth-century sea-level rise. Nature 517, (2015). 6. Cogley, J. G. Geodetic and direct mass-balance measurements: comparison and joint analysis. Ann Glaciol 50, (2009). 7. Slangen, A. B. A., Church, J. A., Zhang, X. & Monselesan, D. Detection and attribution of global mean thermosteric sea-level change. Geophys. Res. Lett. 41, (2014). 8. Domingues, C. M. et al. Improved estimates of upper-ocean warming and multi-decadal sea-level rise. Nature 453, (2008). 9. Kuhlbrodt, T. & Gregory, J. M. Ocean heat uptake and its consequences for the magnitude of sea level rise and climate change. Geophys. Res. Lett. 39, (2012). NATURE CLIMATE CHANGE