Defining a Representative Concentration Pathway for Application

Choosing a Representative Concentration Pathway (RCP) for examination in this project should be based on a consultative process. This part of the manual outlines some of the current thinking we have had on defining RCPs for various clients in project work and given the latest Conference of Party (COP) discussions we have tried to make it as up-to-date as possible and bring to the discussion consideration of Intended Nationally Determined Contributions (INDCs) and potential limitations in societal capacity for achieving not only a reduction in greenhouse gas emissions but a decarbonisation of the world economy. We have taken a pragmatic approach that explores the big picture issues rather than diving deeply into individual and nuanced aspects of each and every possibility that could impact change.

The Representative Concentration Pathways (RCPs) are four greenhouse gas concentration (not emissions) trajectories adopted by the IPCC for its Fifth Assessment Report (AR5). The four RCPs, RCP2.6, RCP4.x, RCP6.0, and RCP8.5, are named after a possible range of radiative forcing values in the year 2100 (of 2.6, 4.x, 6.0, and 8.5 W/m2, respectively) (Table 1).

Table 1. Overview of representative concentration pathways (RCPs) (van Vuuren et al. 2011; Moss et al. 2010; Rojeli et al. 2012)


CO2 Equivalent

SRES Equivalent

Publication – IA Model


Rising radiative forcing pathway leading to 8.5 W/m2 in 2100.



Raiahi et al. 2007 – MESSAGE


Stabilization without overshoot pathway to 6 W/m2 at 2100



Fujino et al.; Hijioka et al. 2008 – AIM


Stabilization without overshoot pathway to 4.x W/m2 2100



Clark et al. 2006; Smith and Wigley 2006; Wise et al. 2009 – GCAM


Peak in radiative forcing at ~ 3 W/m2 before 2100 and decline



van Vuuren et al., 2007; van Vuuren et al. 2006 - IMAGE

a Approximate radiative forcing levels were defined as  ±5% of the stated level in W/m2 relative to pre-industrial levels. Radiative forcing values include the net effect of all anthropogenic GHGs and other forcing agents.

Is 2 °C the Bottomline?

There is plenty of talk of limiting climate change and global warming to 2 degrees C or less from pre-industrial levels. One of the most influential global groups in the G7 +1 that when they met in June of 2015 made strong statements with regard to the Conference of Parties (hereafter COP) negotiations that were to take place at the end of 2015.

The agreement should enhance transparency and accountability including through binding rules at its core to track progress towards achieving targets, which should promote increased ambition over time. This should enable all countries to follow a low-carbon and resilient development pathway in line with the global goal to hold the increase in global average temperature below 2 °C. (G7 +1 Leaders Summit, emphasis added)

The latest COP 21 negotiations have concluded in Paris. They do relate and are linked by previous COP meetings and one of the strongest linkages is with the Copenhagen meeting (COP 15), where Member States agreed to a goal of limiting climate change to no more than 2° C. At the current COP (21) there was considerable – but not universal – support for supplementing this goal with a long-term decarbonization goal, like that included in the G7+1 Leaders Statement in June 2015 and noted above, to provide a signal to business and investors. Many countries wanted to include a decarbonization goal in the Paris agreement, but as a consensus could not be reached to do so, a possible fall-back would be to include the goal in the Conference of the Parties (COP) decision that adopts the Paris agreement, which would give the goal a slightly lesser political status (Bodansky 2015).

Limiting to 2.0 (or better) Degrees Celsius

One of the more critical pieces of country engagement in the COP process has been the development of Intended Nationally Determined Contributions referring to greenhouse gas trajectories (i.e. reductions but not in all country cases) that include: current policy projections; short-term pledges (up to 2030) and long-term pledges (up to 2050) with no explanation of post-2050 targets or implementation guidelines or clear statements on binding commitments.

As of 7 December 2015, 158 submissions to the UNFCCC, reflecting 185 countries (including the European Union member states), and covering around 94% of global emissions in 2010 (excluding LULUCF) and 97% of global population had been made. A further 3% of global emissions are coming from international aviation and maritime transport. Almost 1% of global emissions are covered by countries that are not Parties to the UNFCCC.

Various groups have been analysing the INDCs and what they could mean in relation to the achievement of the target global temperature. Given current commitments and on-going negotiations for decarbonising the global economy pledges look likely to fall short of the 2.0 °C target. Even if the global community were to reach the goal of limiting warming to 2.0 °C there would still be up to 30 cms of sea level rise and important shifts in climate and extreme events that must still be considered in adaptation planning (Wigley 2015).

Importantly there are sizeable gaps between what is stated in the recently submitted INDCs and what history tells us. This is called the emissions gap and there are some very good reasons why this gap may persist for the foreseeable future and even if current pledges are fully realised will leave global temperatures at around 2.7 °C and perhaps higher depending on compliance and rates of reduction achieved.

(Source: Climate Action Tracker Partners 2015)

However, the inertia in the energy system and emissions – e.g. the long lifetime of power plants and other fossil fuel powered technology – sets limits for how quickly nations can realistically slow their emission pathways. Highest emission reduction rates found in the mitigation scenario literature are in the order of 4% to 6% per year, importantly such rates have only been achieved over relatively short periods of time (van Vuuren and Stehfast, 2013). On a longer time frame of 50 years, the maximal rates of reduction observed in scenarios has been only 3% to 4%. Therefore it seems unlikely that most countries could sustain multiyear reduction rates exceeding 4% in the future (Elkholm and Lindroos, 2015).

The 2030 level can affect the achievable future emission levels: being on a higher level initially makes it more difficult to reach a low emission level in the future, as the rate at which emissions can be realistically reduced is limited. The 2030 level can exclude from reaching the target if the further cuts necessary to meet the 2°C target let along 1.5 °C have to be scaled up so fast. This seems highly unlikely given inertia in the energy system and other emission sources (Elkholm and Lindroos, 2015). Underlying such rates of possible emissions reductions beyond international and binding political agreements are national and local issues of politics, institutional capacity and mandates, regulations and standards not only of the UNFCCC but also International Organisation for Standardisation (ISO) and industry requirements. There are also issues of technological capacity and transfer, financial and development stages and goals and equity gaps and financing limitations.

For example, India alone through its submission of its INDC requires significant external financial support for capacity building, technology development and transfer. They noted a need for USD 834 billion to achieve moderate low carbon development up to 2030. The Green Climate Fund update at the COP20 noted a mobilisation of only USD 10.2 billion to date by contributing parties. The target is for USD 100 billion a year by 2020. Even if it were to achieve this level of donor country support India alone could consume eight of the next ten years of funding to meet its needs.

The Green Climate Fund is one of the most divisive issues at COP 21 and there are long standing disagreements on what has and will constitute donations to the fund. There remains a large gap between the expectations of developing countries for significant levels of climate finance, and donor countries, who already feel donor fatigue. A recent report found that $62 billion in climate finance was mobilized in 2014, up from $52 billion in 2013, although these figures are disputed because of the major methodological questions about what should be counted as climate finance (OECD 2015).

What is Best Practice?

Given the confluence of needs for a rapid reduction in greenhouse gas emissions, the slow onset of negotiations to effectuate such change, the move toward non-binding agreements on such reductions is the continued adaptation of a worst case scenario – RCP 8.5 ensemble of models and medium to high sensitivity approach justifiable? And is it even possible when countries or individual clients are not bound by any international standards or national regulations but are free to choose the level of risk they may wish to carry forward through the applications of one of many possible emission pathways. Is this ethical/defensible given the new Intended Nationally Determined Contributions (INDCs)?

What if we try to estimate future scenarios from INDC commitments  . . . theory and practice?

The 158 submissions to date representing 185 countries currently reporting representing about 90 percent of emissions. Clearly there is a greater than 50 percent chance that the global community is not going to make target temperatures and driving emission profiles. Do we therefore advise to plan for a worst case 3.4 °C or 2.7 °C (or 2.2 °C) world for durable 50+ year infrastructure (rather than 4.9 °C +)?


Baseline (1995)

RCP 8.5 (change) to 2030

RCP 8.5 (change) to 2050



27.7 (0.8)

28.4 (1.5)



27.9 (0.8)

28.6 (1.5)



24.x (0.9)

25.2 (1.6)

New Delhi


25.8 (1.2)

26.7 (2.1)

Table 1: Mean annual temperatures and changes in °C to 2030 and 2050 from a baseline of 1995 for RCPs 8.5 medium sensitivity. Global mean temperature change to 2030 for RCP 8.5 is 0.94 °C and for 2050 is 1.70°C, both with medium sensitivity (Warrick et al. 2013).

Coastal and more southern cities at elevation -- as expected -- show less of an increase in temperature than inland and more northern settlements over time owing to the moderating effect of the sea.  Overall when away from the sea India is warming more quickly than the global mean.

In relation to the INDCs that have been submitted there is as shown a general consensus that current pledges will fall short of achieving the 2.0 °C target (and almost certainly the 1.5 °C target suggested by SIDS). Ultimately, can the INDCs and the process be trusted? Monitoring and evaluation is critical and current negotiations are trending toward making it binding to reduce emissions, but actual targets be unbinding (Bodansky 2015; factorCO2 2015).

Given this review the Representative Concentration Pathway RCP8.5 medium sensitivity from IPCC Fifth Assessment Report (IPCC AR5, 2010) it is suggested for application in the Phase One assessments with inclusion of RCP 4.x medium sensitivity as a best case scenario. The natural systems under consideration can be considered lifelines with lifetimes of 100 or more years and thus their resilience to climate risks needs to higher than other variables. Life and property losses could be catastrophic with loss or damage of these natural systems. Furthermore the temperature profile for RCP 8.5 and the time frame for analysis (2030 and 2050) means that even the current goal of limiting temperatures to 2 °C Celsius will be achieved by 2055 (or sooner) under the RCP 8.5 concentration pathway thus planning for the current target temperature is still achieved.

In summary, the RCP8.5 is a greenhouse gas concentration (not emissions) trajectories adopted by the IPCC for its Fifth Assessment Report (AR5) with rising radiative forcing pathway leading to 8.5 W/m2 in 2100.

Figure 1 shows the global mean temperature change projected for RCP8.5, between 1995 and 2100. Global mean temperature change projected ranges from 0.96 °C by 2030 and 4.09 °C by 2100.

Figure 1 The global mean temperature change of the three selected RCP scenarios. The graph shows that up to 2030, global mean temperature is projected to increase by about 1.0oC (from 1995), irrespective of the RCP scenario and subsequently the future temperature change projections diverge by 2050 and even more by 2100, depending on the RCP scenario.


Bodansky, D. (2015). Crunch Issues in Paris. Opinio Juris. Accessed 8 December 2015.

Climate Action Tracker Partners (2015). Climate Action Tracker. Accessed 8 December 2015.

Ekholm, T.; Lindroos, T.J. (2015). An analysis of countries’ climate change mitigation contributions towards the Paris agreement. VTT Technical Research Centre of Finland Ltd.

factor CO2 (2015). INDC Update No.6. 5 November. 2pgs

OECD (2015). Climate finance in 2013-14 and the USD 100 billion goal, a report by the Organisation for Economic Co-operation and Development (OECD) in collaboration with Climate Policy Initiative (CPI).

van Vuuren, D. P.; and Stehfest, E. (2013). If climate action becomes urgent: The importance of response times for various climate strategies. Climatic Change 121, pp. 473–486.

Warrick, R.; Ye, W.; Li, Y.; Dooley, M.; Kouwenhoven, P.; Urich, P, 2013: SimCLIM 2013: A Software System for Modelling the Impacts of Climate Variability and Change. CLIMsystems Ltd. Hamilton, New Zealand.

Wigley, T.M.L. (in press). Intermediate radiative forcing targets and sea level stabilization. Proceedings of the National Academy of Sciences of the United States of America.