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Representative Concentration Pathway

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All forcing agents' atmospheric CO2-equivalent concentrations (in parts-per-million-by-volume (ppmv)) according to the four RCPs used by the fifth IPCC Assessment Report to make predictions.

A Representative Concentration Pathway (RCP) is a greenhouse gas concentration (not emissions) trajectory adopted by the IPCC. Four pathways were used for climate modeling and research for the IPCC fifth Assessment Report (AR5) in 2014. The pathways describe different climate futures, all of which are considered possible depending on the volume of greenhouse gases (GHG) emitted in the years to come. The RCPs; originally RCP2.6, RCP4.5, RCP6, and RCP8.5; are labelled after a possible range of radiative forcing values in the year 2100 (2.6, 4.5, 6, and 8.5 W/m2, respectively).[1][2][3] Since AR5 the original pathways are being considered together with Shared Socioeconomic Pathways: as are new RCPs such as RCP1.9, RCP3.4 and RCP7.[4]

Concentrations

The RCPs are consistent with a wide range of possible changes in future anthropogenic (i.e., human) GHG emissions, and aim to represent their atmospheric concentrations.[5] Despite characterizing RCPs in terms of inputs, a key change from the 2007 to the 2014 IPCC report is that the RCPs ignore the carbon cycle by focusing on concentrations of greenhouse gases, not greenhouse gas inputs.[6] The IPCC studies the carbon cycle separately, predicting higher ocean uptake of carbon corresponding to higher concentration pathways, but land carbon uptake is much more uncertain due to the combined effect of climate change and land use changes.[7]

The four RCPs are consistent with certain socio-economic assumptions but are being substituted with the shared socioeconomic pathways which are anticipated to provide flexible descriptions of possible futures within each RCP. The RCP scenarios superseded the Special Report on Emissions Scenarios projections published in 2000 and were based on similar socio-economic models.[8]

RCPs

RCP 1.9

RCP1.9 is a pathway that limits global warming to below 1.5 °C, the aspirational goal of the Paris Agreement.[4]

RCP 2.6

RCP 2.6 is a "very stringent" pathway.[4]

RCP 3.4

As well as just providing another option a variant of RCP3.4 includes considerable removal of greenhouse gases from the atmosphere.[4]

RCP 4.5

Emissions in RCP 4.5 peak around 2040, then decline.[9]

RCP 6

In RCP 6, emissions peak around 2080, then decline.[9]

RCP 7

RCP7 is a baseline outcome rather than a mitigation target.[4]

RCP 8.5

In RCP 8.5 emissions continue to rise throughout the 21st century.[9] Since AR5 this has been thought to be very unlikely, but still possible as feedbacks are not well understood.[10] The high concentration pathways depend on assumptions of abundant fossil fuel for future production. Researchers have questioned whether remaining world supply can meet such demand. Wang et al conducted a study considering 116 different projections for 21st century fossil fuel production forecasts published in scientific literature and by mainstream energy institutes comprising a wide range of scenarios. The study found that high-concentration pathways may be overestimating future supply of fossil fuels, and in particular RCP8.5 appeared to be an extremely high overestimation.[11] The results indicated that "most climate projections made with current knowledge ... overestimate future climate change due to making what appear to be unrealistic assumptions on the increase in usage of fossil fuels." This study found that a likely upper bound for 21st century CO2 concentration would be about 610ppm, associated with about 2.6 degrees of warming above pre-industrial levels. The study also indicated, however, that even under these supply constraints, CO2 concentration and warming were still likely to exceed the accepted "dangerous" level of 410 ppm and 2 degrees, respectively, by 2100.

Hausfather and Peters indicated in a comment in Nature that RCP8.5, generally taken as the basis for worst-case climate change scenarios, was based on what proved to be overestimation of projected coal outputs. This has rendered the RCP8.5 scenario "increasingly implausible with each passing year." [12]

David Rutledge wrote on coal use: "The estimate for long-term world production is 680 Gt, compared with the reserves plus cumulative production, 1163 Gt. [..] The calculated year of 90% exhaustion is 2070. This gives a time frame for the development of alternatives. This work does not support the use of multiples of coal reserves in the IPCC scenarios." [13]

In 2016, a study found that, although world oil production increased in the early-mid 2010s, these increases were mainly due to high growth in production of light tight oil (LTO) in the United States, with the rest of world oil production remaining constant. The study concluded that if US LTO production were to decline persistently, it would be unlikely that demand for oil production required under the higher-concentration scenarios of RCP8.5 and RCP6 could be met.[14] The U.S. Energy Information Administration projected in its January 2020 Annual Energy Outlook that US oil production would reach a plateau from 2022 through 2045, and enter into decline thereafter as development moves into less productive areas and well-productivity declines.[15]

Projections based on the RCPs

21st century

Mid- and late-21st century (2046–2065 and 2081–2100 averages, respectively) projections of global warming and global mean sea level rise from the IPCC Fifth Assessment Report (IPCC AR5 WG1) are tabulated below. The projections are relative to temperatures and sea levels in the late-20th to early-21st centuries (1986–2005 average). Temperature projections can be converted to a reference period of 1850–1900 or 1980–99 by adding 0.61 or 0.11 °C, respectively.[16]

AR5 global warming increase (°C) projections[16]
2046–2065 2081–2100
Scenario Mean and
likely range		 Mean and
likely range
RCP2.6 1.0 (0.4 to 1.6) 1.0 (0.3 to 1.7)
RCP4.5 1.4 (0.9 to 2.0) 1.8 (1.1 to 2.6)
RCP6 1.3 (0.8 to 1.8) 2.2 (1.4 to 3.1)
RCP8.5 2.0 (1.4 to 2.6) 3.7 (2.6 to 4.8)

Across all RCPs, global mean temperature is projected to rise by 0.3 to 4.8 °C by the late-21st century.

AR5 global mean sea level (m) increase projections[16]
2046–2065 2081–2100
Scenario Mean and
likely range		 Mean and
likely range
RCP2.6 0.24 (0.17 to 0.32) 0.40 (0.26 to 0.55)
RCP4.5 0.26 (0.19 to 0.33) 0.47 (0.32 to 0.63)
RCP6 0.25 (0.18 to 0.32) 0.48 (0.33 to 0.63)
RCP8.5 0.30 (0.22 to 0.38) 0.63 (0.45 to 0.82)

Across all RCPs, global mean sea level is projected to rise by 0.26 to 0.82 m by the late-21st century.

23rd century

AR5 also projects changes in climate beyond the 21st century. The extended RCP2.6 pathway assumes sustained net negative anthropogenic GHG emissions after the year 2070.[5] "Negative emissions" means that in total, humans absorb more GHGs from the atmosphere than they release. The extended RCP8.5 pathway assumes continued anthropogenic GHG emissions after 2100.[5] In the extended RCP 2.6 pathway, atmospheric CO2 concentrations reach around 360 ppmv by 2300, while in the extended RCP8.5 pathway, CO2 concentrations reach around 2000 ppmv in 2250, which is nearly seven times the pre-industrial level.[5]

For the extended RCP2.6 scenario, global warming of 0.0 to 1.2 °C is projected for the late-23rd century (2281–2300 average), relative to 1986–2005.[17] For the extended RCP8.5, global warming of 3.0 to 12.6 °C is projected over the same time period.[17]

See also

References

  1. ^ "Representative Concentration Pathways (RCPs)". IPCC. Retrieved 13 February 2019.
  2. ^ Richard Moss; et al. (2008). Towards New Scenarios for Analysis of Emissions, Climate Change, Impacts, and Response Strategies (PDF). Geneva: Intergovernmental Panel on Climate Change. p. 132.
  3. ^ Weyant, John; Azar, Christian; Kainuma, Mikiko; Kejun, Jiang; Nakicenovic, Nebojsa; Shukla, P.R.; La Rovere, Emilio; Yohe, Gary (April 2009). Report of 2.6 Versus 2.9 Watts/m2 RCPP Evaluation Panel (PDF). Geneva, Switzerland: IPCC Secretariat.
  4. ^ a b c d e "Explainer: How 'Shared Socioeconomic Pathways' explore future climate change". Carbon Brief. 2018-04-19. Retrieved 2020-03-04.
  5. ^ a b c d Collins, M., et al.: Section 12.3.1.3 The New Concentration Driven RCP Scenarios, and their Extensions, in: Chapter 12: Long-term Climate Change: Projections, Commitments and Irreversibility (archived 16 July 2014), in: IPCC AR5 WG1 2013, pp. 1045–1047
  6. ^ IPCC 2013: Technical Summary (PDF) (Report). the uncertainty is now estimated to be smaller than with the AR4 method for long-term climate change, because the carbon cycle–climate feedbacks are not relevant for the concentration-driven RCP projections
  7. ^ IPCC AR5- Technical Summary- TFE.7 Carbon Cycle Perturbation and Uncertainties (PDF) (Report). With very high confidence, ocean carbon uptake of anthropogenic CO2 emissions will continue under all four Representative Concentration Pathways (RCPs) through to 2100, with higher uptake corresponding to higher concentration pathways. The future evolution of the land carbon uptake is much more uncertain, with a majority of models projecting a continued net carbon uptake under all RCPs, but with some models simulating a net loss of carbon by the land due to the combined effect of climate change and land use change. In view of the large spread of model results and incomplete process representation, there is low confidence on the magnitude of modelled future land carbon changes.
  8. ^ Ward, James D.; Mohr, Steve H.; Myers, Baden R.; Nel, William P. (December 2012). "High estimates of supply constrained emissions scenarios for long-term climate risk assessment". Energy Policy. 51: 598–604. doi:10.1016/j.enpol.2012.09.003.
  9. ^ a b c Figure 2, in Meinshausen & others 2011, p. 223
  10. ^ "BBC World Service - The Inquiry, Have our climate models been wrong?". BBC. Retrieved 2020-03-05.
  11. ^ Wang, Jianliang; Feng, Lianyong; Tang, Xu; Bentley, Yongmei; Höök, Mikael (February 2017). "The implications of fossil fuel supply constraints on climate change projections: A supply-side analysis". Futures. 86 (2): 58–72. doi:10.1016/j.futures.2016.04.007.
  12. ^ Hausfather, Zeke; Peters, Glen (29 January 2020). "Emissions – the 'business as usual' story is misleading". Nature. 577 (7792): 618–20. doi:10.1038/d41586-020-00177-3. PMID 31996825.
  13. ^ Rutledge, David (2011-01-01). "Estimating long-term world coal production with logit and probit transforms". International Journal of Coal Geology. 85 (1): 23–33. doi:10.1016/j.coal.2010.10.012. page 32
  14. ^ Murray, James (1 December 2016). "Limitations of Oil Production to the IPCC Scenarios: The New Realities of US and Global Oil Production". BioPhysical Economics and Resource Quality. 1 (2): 13. doi:10.1007/s41247-016-0013-9.
  15. ^ Annual Energy Outlook 2020 with Projections to 2050 (PDF) (Report). U.S. Energy Information Administration. January 2020. p. 4.
  16. ^ a b c IPCC: Table SPM-2, in: Summary for Policymakers (archived 16 July 2014), in: IPCC AR5 WG1 2013, p. 21
  17. ^ a b Collins, Matthew, et al.: Executive summary, in: Chapter 12: Long-term Climate Change: Projections, Commitments and Irreversibility (archived 16 July 2014), in: IPCC AR5 WG1 2013, p. 1033

Note: The following references are cited in this article using Template:Harvard citation no brackets:

  • Meinshausen, M.; et al. (November 2011), "The RCP greenhouse gas concentrations and their extensions from 1765 to 2300 (open access)", Climatic Change, 109 (1–2): 213–241, doi:10.1007/s10584-011-0156-z.

External links

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