Research ArticleOCEANOGRAPHY

Dependence of regional ocean heat uptake on anthropogenic warming scenarios

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Science Advances  06 Nov 2020:
Vol. 6, no. 45, eabc0303
DOI: 10.1126/sciadv.abc0303
  • Fig. 1 CMIP5-simulated OHU changes under the RCP2.6 and RCP8.5 scenarios.

    Top row: CMIP5 MME OHU trends during 2006–2100 under the (A) RCP2.6 and (B) RCP8.5 scenarios. Stippling denotes where the OHU trends are statistically significant at the 95% confidence level based on the Student’s t test. Positive (negative) values mean ocean gains (losses) heat. Bottom row: Annual mean OHU anomalies of CMIP5 model averaged over the North Atlantic (35°N to 70°N, 80°W to 10°W; MME, blue curve; model spread, blue shading) and averaged over the Southern Ocean (35°S to 70°S, 0° to 360°; MME, pink curve; model spread, pink shading) during 2006–2100 under the (C) RCP2.6 and (D) RCP8.5 scenarios. Anomalies are relative to the 2006–2025 mean. Model spread is represented by 1 SD of model results. Southern Ocean OHU anomalies are multiplied by a factor of 3 for a better illustration.

  • Fig. 2 Relationships between aerosol ERFs and regional OHU trends in CMIP5 models over the 21st century under the RCP2.6 and RCP8.5 scenarios.

    Top row: Aerosol ERFs of 2000 relative to 1850 and North Atlantic OHU trends of 2006–2100 under the (A) RCP2.6 and (B) RCP8.5 scenarios in CMIP5 models. Bottom row: As in the top row but for aerosol ERFs and Southern Ocean OHU trends (C and D). Models are denoted by different colors. Models with no aerosol indirect effects (G1: NO AIE) are denoted by circles. Models with only the first aerosol indirect effects, cloud albedo effects (G2: AIE1), are denoted by triangles. Models with both aerosol indirect effects, cloud albedo and cloud lifetime effects (G3: AIE1 + AIE2), are denoted by squares. Solid black line in each panel represents the linear regression line for the scatters. Correlation coefficient (r) between ERFs and OHU trends and P value are noted in each case. Notice the different scales in each panel.

  • Fig. 3 CESM1-CAM5 OHU trends under the RCP2.6 and RCP8.5 scenarios and aerosol effects on OHU trends.

    Left column: OHU trends during 2006–2100 (A) in rcp26 and (C) rcpFA26 simulations with CESM1-CAM5 and (E) for their difference (rcp26-rcpFA26), which indicates aerosol effects. Right column: As in the left column but for (B) rcp85 and (D) rcpFA85 and (F) their difference. Stippling denotes where trends are statistically significant at the 95% confidence level based on the Student’s t test. Positive (negative) values mean ocean gains (losses) heat.

  • Fig. 4 CESM1-CAM5 regional OHU time series under the RCP2.6 and RCP8.5 scenarios.

    Top row: Annual mean OHU anomalies averaged over the North Atlantic (NA) (35°N to 70°N, 80°W to 10°W) during 2006–2100 under the (A) RCP2.6 and (B) RCP8.5 scenarios. Bottom row: As in the top row but for annual mean OHU anomalies averaged over the Southern Ocean (SO) (35°S to 70°S, 0° to 360°) (C and D). Thick black and blue curves indicate OHU anomalies in rcp and rcpFA simulations with CESM1-CAM5, which are calculated from the ensemble means of individual simulations. Thin black and blue curves denote OHU anomalies for three ensemble members in each of the rcp and rcpFA simulations. Orange lines denote the difference between the ensemble means of rcp and rcpFA simulations, which indicate aerosol effects. OHU anomalies are relative to the 2006–2025 mean and a 5-year running mean is applied. Notice the different scales in each panel.

  • Fig. 5 CESM1-CAM5 aerosol effects on OHU and ocean heat redistribution under the RCP2.6 (left) and RCP8.5 (right) scenarios.

    Left column: Differences of annual mean (A) OHU (positive into the ocean); (C) OHS (positive values mean increases of heat in the ocean); (E) meridional overturning streamfunction in the Atlantic (negative values denote the weakening of meridional circulation); (G) OHT in the Atlantic (positive values denote anomalous northward heat transport): heat transport induced by total advection (solid), Eulerian-mean advection (dashed), and their residual (dotted; including eddy-induced advection and sub-mesoscale advection); (I) heat budget in the Atlantic: zonally integrated full-depth OHS (red), zonally integrated OHU (black), divergence of OHT induced by advections (blue), and zonally integrated full-depth heat change due to diffusive processes (green) during 2006–2100 under the RCP2.6 scenario. Right column: As in the left column but for the RCP8.5 scenario (B, D, F, H, and J). Stippling in the top six panels denotes where differences are statistically significant at the 95% confidence level based on the Student’s t test. In the bottom four panels, dark colors (relative to light colors) denote where differences are statistically significant at the 95% confidence level based on the Student’s t test. Contours in (E) and (F) denote the annual mean AMOC averaged over 2006–2100 under the RCP2.6 and RCP8.5 scenarios, respectively. Curves in (I) and (J) are derived after a 7.5° running mean.

Supplementary Materials

  • Supplementary Materials

    Dependence of regional ocean heat uptake on anthropogenic warming scenarios

    Xiaofan Ma, Wei Liu, Robert J. Allen, Gang Huang, Xichen Li

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