Review

Contrasting futures for ocean and society from different anthropogenic CO2 emissions scenarios

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Science  03 Jul 2015:
Vol. 349, Issue 6243, aac4722
DOI: 10.1126/science.aac4722

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  1. Changes in ocean physics and chemistry and impacts on organisms and ecosystem services according to stringent (RCP2.6) and high business-as-usual (RCP8.5) CO2 emissions scenarios.

    Changes in temperature (∆T) and pH (∆pH) in 2090 to 2099 are relative to preindustrial (1870 to 1899). Sea level rise (SLR) in 2100 is relative to 1901. RCP2.6 is much more favorable to the ocean, although important ecosystems, goods, and services remain vulnerable, and allows more-efficient management options. l, m, h: low, mid-, and high latitudes, respectively.

  2. Fig. 1 Environmental changes over the industrial period and the 21st century for a business-as-usual scenario and a stringent emissions scenario consistent with the UNFCCC target of increase in global surface temperature by 2°C.

    (A to E) Changes in globally averaged (A) SST, (B) sea level, (C) sea surface pH (total pH scale), (D) ocean volume (in % of total ocean volume) with saturation state of calcium carbonate in aragonitic form (Ωa) above 1 and above 3, and (E) dissolved oxygen. RCP8.5, red lines; RCP2.6, blue lines. Maps show the 21st century changes in SST (F and G) and in sea surface pH (H and I) for RCP8.5 (top) and RCP2.6 (bottom), respectively. All projected values represent ensemble mean values from the Coupled Model Intercomparison Project 5 [CMIP5 (23)].

  3. Fig. 2 Observed impact and risk scenarios of ocean warming and acidification for important organisms and critical ecosystem services.

    “Present-day” (gray dotted line) corresponds to the period from 2005 to 2014. Impact levels are for the year 2100 under the different projections shown and do not consider genetic adaptation, acclimatization, or human risk reduction strategies (mitigation and societal adaptation). RCP4.5 is shown for illustrative purposes as an intermediate scenario between the business-as-usual high-emissions scenario (RCP8.5) and the stringent reduction scenario (RCP2.6). (A) Changes in global average SST and pH versus cumulative fossil fuel emissions. Realized fossil emissions (26) are indicated for different years below the horizontal axis, whereas the lines are based on allowable emissions estimated from ensemble means of the CMIP5 simulations for the industrial period and the 21st century following RCP2.6, RCP4.5, and RCP8.5 (23). Cumulative emission of 1000 GtC causes a global SST change of about 1.7°C and a surface pH change of about –0.22 units. The colored shadings indicate the 68% confidence interval for pH (gray) and SST (pink) from observation-constrained, probabilistic projections using 55 multi–gas emissions scenarios (24). (B) Risk of impacts resulting from elevated CO2 on key organisms that are well documented in the literature. (C) Risk of impacts resulting from elevated CO2 on critical ecosystem services. The levels of confidence in the risk levels synthesize the author team’s judgments (see materials and methods) about the validity of findings as determined through evaluation of evidence and agreement (157).

  4. Fig. 3 Regional changes in the physical system and associated risks for natural and human-managed systems.

    Projected changes in SST (ΔSST) and pH (ΔpH) in 2090–2099 relative to preindustrial under the RCP2.6 and RCP8.5 scenarios are displayed in different colors on the map. The major ocean regions are indicated as well as examples of risks for natural systems and fisheries [modified from (1)]. Text in parentheses specifies the level of confidence (157).

  5. Fig. 4 Four clusters of actions against climate change, including ocean acidification.

    For each cluster, a nonexhaustive list of actions is shown. [CO2]atm is concentration of atmospheric CO2; GH, greenhouse; GHG, greenhouse gases; MPAs, marine protected areas. The mitigation pathway leading to CO2 reductions is represented in bold, consistent with the consensus view that significant reductions in CO2 emissions is presently the only actual “solution” to the ocean impacts of climate change and ocean acidification (see main text).