The Representative Concentration Pathway 8.5 (RCP8.5) stands as a critical scenario in climate change research, providing a high-end projection of future greenhouse gas (GHG) emissions and their potential impacts. This article delves into the storyline and main drivers of RCP8.5, offering a Comparatively detailed examination of its energy system, land-use changes, and emissions trajectory. We will further explore the implications of mitigation measures within this high-emission context, contrasting it with other scenarios and historical trends to provide a comprehensive understanding of its significance.
1. Storyline and Main Scenario Drivers of RCP8.5
RCP8.5 is rooted in the A2r scenario, an updated iteration of the original IPCC A2 SRES scenario storyline. With minor adjustments, such as an updated base year (2005) and refined short-term energy trend representations, particularly in developing nations, RCP8.5 largely inherits the socio-economic, demographic, resource, and technological foundations of A2r.
The narrative underpinning this scenario portrays a heterogeneous world characterized by continuous global population growth, reaching a substantial 12 billion by 2100. Income growth per capita is projected to be sluggish, with limited convergence between high and low-income countries both internationally and regionally. The global Gross Domestic Product (GDP) is estimated to reach approximately 250 trillion US2005 dollars by 2100. This modest economic advancement also implies limited progress in efficiency improvements. Coupled with significant population expansion, this results in substantial energy demands.
Moreover, international trade in energy and technology is assumed to be constrained, and the overall pace of technological progress remains moderate. The scenario emphasizes self-reliance for individual countries and regions, leading to a greater dependence on domestically available resources. While resource availability isn’t necessarily a limiting factor, easily accessible conventional oil and gas resources become comparatively scarce relative to unconventional fuels like tar sands or oil shale, which are more challenging to exploit. Given the slow advancement in low-carbon technologies, the energy system in this scenario tends towards coal-intensive technology choices, resulting in elevated GHG emissions. Environmental concerns, while locally significant, particularly in high and medium-income regions, are not prioritized globally to the extent of driving strong climate mitigation policies. Food security emerges as a major concern, especially in lower-income regions, necessitating increases in agricultural productivity to sustain the growing population.
Figure 1: Global development of main scenario drivers in RCP 8.5 (red lines) compared to the range of scenarios from the literature (grey areas). This figure highlights the comparatively high population and intermediate GDP projections of RCP8.5.
Comparatively speaking, within the broader integrated assessment literature, RCP8.5 represents a scenario characterized by high global population growth and intermediate GDP development. However, per capita income remains at comparatively low levels, approximately 20,000 US$2005 in 2100, falling significantly below the median of other assessed scenarios. Another defining feature of RCP8.5 is its relatively slow rate of improvement in primary energy intensity, at just 0.5% per year throughout the century. This sluggish improvement reflects the storyline’s assumption of modest technological change. These rates are considerably below the historical average of approximately 1% per year observed between 1940 and 2000. In contrast to other scenarios, RCP8.5 portrays a comparatively conservative business-as-usual trajectory with lower income, high population, and elevated energy demand due to minimal advancements in energy intensity.
2. Development of the Energy System
2.1 Energy System of RCP8.5
As previously mentioned, RCP8.5 is a baseline scenario devoid of explicit climate policies, representing the highest RCP in terms of GHG emissions. This section initially outlines the primary energy system shifts within the RCP8.5 baseline. Subsequently, it analyzes the necessary GHG emission reductions to limit radiative forcing to levels comparatively similar to other RCPs. The focus here is primarily on the energy system transition, with subsequent sections addressing land-use and GHG and pollutant emissions.
Driven by a growing population and economy, coupled with assumptions of slow energy efficiency improvements, RCP8.5 projects a substantial surge in primary energy demand, nearly tripling over the century. This escalating demand is predominantly met by fossil fuels within RCP8.5. Two key factors contribute to this trend. Firstly, the scenario posits a comparatively slow pace of innovation in advanced non-fossil technologies, leading to modest cost and performance enhancements. Consequently, fossil fuel technologies remain economically more attractive in RCP8.5. Secondly, the availability of vast unconventional fossil resources extends fossil fuel utilization beyond currently extractable reserves. However, the cumulative extraction of unconventional fossil resources remains within the theoretical upper bounds found in literature.
Figure 2: Development of global primary energy supply in RCP8.5 (left-hand panel) and in mitigation cases (right-hand bars). This figure comparatively illustrates the dominance of fossil fuels in RCP8.5 versus the shift towards non-fossil sources in mitigation scenarios.
Coal consumption, in particular, witnesses an almost tenfold increase by 2100, and there is a sustained reliance on oil in the transportation sector. This continued dependence on fossil fuels does not necessarily imply a complete absence of technological progress. Comparatively, significant advancements are observed in existing fossil fuel alternatives and the adoption of new advanced fossil technologies, enhancing their efficiency and performance over the long term. In the electricity sector, this manifests as a transition towards cleaner coal technologies, moving away from current sub-critical coal capacities. Furthermore, as conventional oil becomes increasingly scarce, a shift towards more expensive unconventional oil sources occurs by 2050. The subsequent rise in fossil fuel prices also stimulates increased adoption of “synthetic” fuels, such as coal-based liquids. This increase in fossil fuel prices (approximately doubling for both natural gas and oil by mid-century) also encourages some growth in nuclear electricity and hydropower, particularly in the long term. However, overall, fossil fuels continue to dominate the primary energy portfolio throughout the RCP8.5 scenario’s timeframe.
In terms of final energy consumption, significant transformations occur in how energy is utilized within RCP8.5. Electricity, in particular, continues its historical growth trajectory, becoming the dominant mode of energy use, primarily in the residential sector and partially in the industrial sector. In the long term (beyond 2050), electricity in RCP8.5 is largely supplied from non-fossil sources, namely nuclear and biomass.
Figure 3: Development of global final energy in RCP8.5 (left-hand panel) and in mitigation cases (right-hand panel). This figure comparatively shows the increasing share of electricity in final energy consumption in both RCP8.5 and mitigation scenarios.
2.2 Impact of Mitigation Measures
The high energy demand and fossil fuel intensity associated with RCP8.5 underscore that achieving climate stabilization necessitates substantial emission reductions and dramatic energy system transformations comparatively greater than in lower baseline scenarios. Previous research suggested that achieving low climate stabilization levels from the A2r scenario—the predecessor to RCP8.5—might be technically infeasible. These earlier studies employed a qualitative criterion that restricted energy intensity improvements for stabilization targets to remain within relatively narrow bounds of the baseline scenario storyline. However, this assessment allows for more pronounced reductions in energy demand beyond these criteria. It observes that achieving a 2.6 W/m2 target under a fossil-intensive RCP8.5 scenario becomes feasible if more rapid energy intensity improvements are achievable.
Beyond energy demand responses, this analysis considers various options for reducing energy-related CO2 emissions on the supply side. These include transitioning from fossil fuels to renewable or nuclear power, switching to lower-carbon fossil fuels (e.g., from coal to natural gas), and implementing carbon capture and storage (CCS) technologies for both fossil and biomass sources. The analysis also encompasses the full range of non-CO2 GHGs and related mitigation options, both energy-related (e.g., extraction and transport of fossil fuels) and non-energy-related (e.g., livestock, waste management, agriculture).
The primary energy mix for climate mitigation scenarios aiming for radiative forcing levels of 6, 4.5, and 2.6 W/m2 by the end of the century are depicted in Figure 2. In the short and medium term, transition technologies like fossil-based CCS (particularly natural gas with CCS) become comparatively more important. In the longer term, dominant technological solutions include energy conservation and efficiency improvements, nuclear energy, and biomass with carbon capture (BECCS). This trend remains consistent across all analyzed stabilization targets but is most pronounced in the stringent 2.6 W/m2 forcing scenario. While renewable electricity sources like solar PV increase their contribution in the long term, the majority of carbon-free electricity originates from centralized nuclear and biomass power plants. This technology preference reflects the underlying storyline of RCP8.5 and its associated technology assumptions, which favor traditional centralized supply options, including fossil CCS, nuclear, and biomass. The results highlight that lower stabilization goals might be attainable even from high baselines like RCP8.5. Moreover, mitigation solutions may not necessarily require a complete shift from large-scale centralized energy production to dispersed intermittent sources.
In terms of final energy, the pace of electrification accelerates further in climate mitigation scenarios. Non-fossil electricity becomes a major driver of decarbonization, leading to electricity shares in final energy reaching approximately 60% by 2100, comparatively higher than the 30% in RCP8.5. Oil consumption peaks around mid-century and declines in the long term. In RCP8.5, the resulting gap in liquid fuel supply is filled by other liquefaction processes, such as coal- and biomass-based liquids. In climate mitigation scenarios, hydrogen emerges as an additional significant long-term final energy carrier in the transport sector. The transition away from oil products towards electricity and hydrogen has wide-ranging consequences, including improved regional energy security due to reduced oil dependency and major environmental benefits through decreased pollutant emissions, particularly in urban areas.
Figure 4: Long-term energy intensity and carbon intensity improvement rates for RCP8.5 and mitigation scenarios compared to historical trends and other SRES scenarios. This figure comparatively illustrates the significantly accelerated decarbonization required for stringent mitigation targets.
Figure 4 comparatively illustrates the required pace of energy intensity and carbon intensity improvements in RCP8.5 and mitigation scenarios against historical trends and selected scenarios from literature (SRES B1 and B2). Reducing GHG emissions necessitates both demand-side changes (energy intensity improvements) and supply-side structural changes (carbon intensity improvements). The required pace of transition is particularly challenging for the low 2.6 W/m2 target. For example, in terms of carbon intensity, the 2.6 W/m2 scenario exhibits a six-fold increase in the rate of decarbonization compared to the RCP8.5 baseline. This also represents a major trend break and a five-fold acceleration of decarbonization compared to the long-run historical improvement rate. Regarding energy intensity, the 2.6 W/m2 target is comparatively less ambitious, depicting improvement rates roughly in line with historical trends between 1940 and 2000, around 1% per year. This rate is also comparable to assumptions in intermediate baseline scenarios like the B2 SRES. While this improvement rate is modest considering the stringent climate target, it still signifies a drastic departure from the RCP8.5 baseline, where energy intensity improves at only half this rate (0.5% per year). These results highlight the importance of path dependency and the conditionality of transformation strategies based on the chosen baseline and its underlying assumptions. Achieving any of the climate targets would necessitate a different mix of measures and costs if, for example, the sustainable SRES B1 scenario with its comparatively high rates of improvement were used as the counterfactual.
3. Land-Use and Land-Cover Change
Currently, approximately 1.6 billion hectares of land are used for crop production globally, with nearly 1 billion hectares under cultivation in developing countries. Over the past 30 years, the world’s crop area has expanded by roughly 5 million hectares annually, with Latin America accounting for 35% of this increase. The potential for arable land expansion is primarily concentrated in South America and Africa, where just seven countries hold 70% of this potential. Asia, home to approximately 60% of the global population, offers comparatively limited scope for arable land expansion. These constraints are reflected in the land-use change dynamics of the RCP8.5 scenario.
Projected global cultivated land use in RCP8.5 increases by approximately 185 million hectares between 2000 and 2050, and an additional 120 million hectares from 2050 to 2100. While aggregate arable land use in developed countries slightly decreases, all net increases occur in developing countries. Africa and South America together account for 85% of this expansion. This significant expansion in agricultural resource use is driven by the socio-economic context of the underlying emission scenario, characterized by a population increase to over 10 billion by 2050 and 12 billion by 2100. Even with this expansion, yield improvements and intensification are assumed to contribute to most of the required production increases. While global agricultural output in the scenario increases by 85% until 2050 and 135% until 2080, cultivated land expands by 12% and 16% above year 2000 levels, respectively.
Figure 5: Global land use by category in RCP8.5. This figure illustrates the comparatively large increase in cultivated land and managed forests under the RCP8.5 scenario.
A key feature of RCP8.5 is the transformative shift in biomass use for energy purposes. It moves from predominantly traditional (non-commercial) use in the developing world to commercial use in dedicated bio-energy conversion facilities in the future. Globally, bioenergy contribution in RCP8.5 increases from approximately 40 EJ in 2000 to over 150 EJ by 2100. The majority of this biomass is harvested from forests, leading to increased land requirements for secondary managed forests. While the total forest area declines in RCP8.5, the share of managed forests and harvested areas for biomass increases considerably. The latter grows from approximately 17 million hectares to over 26 million hectares by 2100. However, significant uncertainties exist in the interpretation of underlying land developments. Estimates for land requirements for wood harvest can vary significantly, highlighting the need for further harmonization of underlying data and definitions in forest models.
4. GHG Emissions
4.1 GHG Emissions in RCP8.5
GHG emissions in RCP8.5 continue to rise due to the high fossil fuel intensity of the energy sector and increasing population and food demand. The development of main GHG emissions in RCP8.5 and corresponding mitigation scenarios are shown in Figure 6. RCP8.5 emissions are high, not only compared to the overall emissions scenario literature but also compared to other baseline scenarios. In RCP8.5, CO2-eq. emissions more than double by 2050 and triple to approximately 120 GtCO2-eq. by 2100 (relative to 2000). Roughly three-quarters of this increase is attributed to rising CO2 emissions from the energy sector. The remaining increase is primarily due to increased fertilizer use and agricultural intensification, the main sources of N2O emissions. Additionally, increases in livestock population, rice production, and enteric fermentation processes drive methane (CH4) emissions.
Figure 6: Development of global GHG emissions in RCP8.5 and mitigation scenarios. This figure comparatively shows the high GHG emissions trajectory of RCP8.5 in contrast to the significant reductions required for mitigation scenarios.
The high GHG emissions in RCP8.5 necessitate large-scale emission reductions to limit radiative forcing to levels comparatively similar to other RCPs. Mitigation potentials from livestock and agricultural sectors are estimated to be limited, with global mitigation potential capped at approximately 50% and 30% of RCP8.5 baseline emissions for CH4 and N2O, respectively. This explains the comparatively limited role of CH4 and N2O emissions mitigation in these mitigation scenarios compared to other RCPs like RCP2.6, RCP4.5, and RCP6.
4.2 GHG Emissions in Mitigation Scenarios
The comparatively limited potential for non-CO2 mitigation options in RCP8.5 means that the majority of emission reductions in the long term must come from CO2 in the energy sector. Cumulative CO2 emissions in RCP8.5 total approximately 7300 GtCO2 over the century. To limit forcing to 6 W/m2, about 40% of these emissions must be avoided. More stringent targets require further emission mitigation, with 60% and 87% reductions of RCP8.5 emissions needed to stay below the 4.5 and 2.6 W/m2 targets, respectively. These cumulative mitigation requirements have significant implications for emission pathways, which, in all mitigation scenarios, are characterized by a peak and decline in CO2 emissions.
The peak of emissions in the scenario leading to 6 W/m2 occurs around mid-century. However, if emission growth over the next decades is slower, as in RCP6, the same target could be achieved with a later peaking date around 2080. Staying below 2.6 W/m2 demands much more rapid emission reductions, allowing for comparatively limited flexibility in the emission peak. Both RCP2.6 and the 2.6 W/m2 scenario indicate that emissions must peak before approximately 2020. However, there are important differences in CO2 emission pathways, particularly regarding the required negative emissions to limit forcing below 2.6 W/m2. There is a comparatively greater need for negative emissions in this scenario compared to RCP2.6. This difference is mainly due to higher non-CO2 emissions, which are compensated by more pronounced negative CO2 emissions in the long term.
5. Emission of Air Pollutants
5.1 Air Pollutants in RCP8.5
While RCP8.5 represents baseline developments without climate mitigation policies, air quality legislation significantly influences pollutant emission projections. Unlike climate policies, air quality measures have already been implemented in many regions globally. RCP8.5 assumes the successful implementation of current and planned environmental legislation until 2030. Beyond 2030, increasing affluence is assumed to lead to stricter pollutant legislation in the long term.
RCP8.5 explicitly considers varying levels of legislation, economic growth, and technological progress across regions, resulting in regionally diverse emission intensity developments. Air quality standards are currently highest in OECD countries. Emission intensities in OECD nations are already comparatively low, and planned legislation is expected to further reduce them by 2030. Economies in transition and regions with medium development are projected to experience the most significant declines in emission intensities across all regions by 2030, reflecting stricter policies, particularly in the power and transportation sectors. Low-income regions, characterized by modest air quality controls, show the least pronounced declines in emission coefficients to 2030, reflecting a lack of concrete short-term legislative plans.
Figure 7: Illustrative examples for the development of emissions intensities for different pollutants and sectors. This figure comparatively highlights the varying emission intensity trends across different regions and development stages.
In RCP8.5, many regions experience economic catch-up beyond 2030, reaching income levels exceeding $5000 per capita. Beyond this point, these regions follow the Environmental Kuznets Curve (EKC) assumptions of declining emission coefficients. Additionally, a significant trend in RCP8.5 is the pervasive shift towards cleaner fuels and advanced fossil technologies in the energy system, which, combined with EKC assumptions, explains the long-term decline in pollutant emission intensities. For example, in the power sector, SO2 emissions reductions result from both tightening legislation and the increasing adoption of inherently cleaner coal technologies.
Assumptions about environmental legislation, combined with ongoing structural and technological change, imply significant pollutant emission declines in RCP8.5, as seen in the example of SO2 emissions. Growing regional environmental concerns, coupled with the absence of a global climate change regime, result in a clear decoupling of CO2 emissions from pollutants. While the power sector remains a major CO2 emitter by the end of the century, SO2 emissions from this sector become almost negligible due to the increased use of advanced coal technologies. In the transport and residential sectors, CO2 emissions continue to rise globally, while pollutant emissions in most developing regions either slow down or decline where air quality legislation is stringent enough to offset growing demand. Thus, while RCP8.5 represents the highest GHG emission scenario among the RCP set, it is not necessarily a ‘high pollution’ scenario in terms of air pollutants.
Figure 8: Distribution of SO2 Emissions in RCP8.5 for the years 2000, 2020, 2050, and 2100. This figure comparatively shows the spatial dynamics of SO2 emissions, with initial increases in developing Asia followed by global declines.
Figure 9: Global SO2 Emissions by sector in RCP8.5 and mitigation scenarios. This figure comparatively illustrates the co-benefit of climate mitigation policies in reducing SO2 emissions.
While globally aggregated pollutant trends show continuous improvements and emission declines, significant regional and spatial differences exist, with local implications for human health, environment, and climate change. The spatial dynamics of SO2 emissions in RCP8.5 illustrate these regional variations. Initially, most reductions occur in OECD countries, while developing regions, particularly Asia, continue to experience growth in SO2 emissions due to increasing energy demands. This highlights that current environmental policies may be insufficient to reduce pollution levels in rapidly growing economies where energy demand growth offsets the effects of control policies. However, in the long term, increasing affluence and technological shifts in these regions lead to significant declines in global emission levels, reducing the global impacts from pollutants.
5.2 Air Pollutants in Mitigation Scenarios
Climate mitigation scenarios demonstrate significant co-benefits for pollutant emissions. GHG emission reductions in mitigation scenarios lead to major improvements in carbon and energy intensity compared to the RCP8.5 baseline. The shift to carbon-free and non-fossil technologies is generally associated with lower pollutant emissions. Furthermore, CCS application requires cleaner combustion processes, further reducing pollutant emissions in mitigation scenarios. Crucially, higher rates of energy intensity improvements in climate mitigation scenarios lead to significant energy savings, reducing both climate impacts and pollution.
The co-benefit of climate mitigation for pollutants is particularly pronounced in the short to medium term. For instance, the 2.6 W/m2 scenario reduces global SO2 emissions by approximately 55% in 2030 compared to the year 2000. This steep decline roughly doubles the pollutant emission reductions compared to the RCP8.5 baseline (25% reductions in 2030 compared to 2000). In essence, stringent climate mitigation can reduce pollutant emissions by a magnitude comparable to the entire existing and planned air pollution policy landscape.
