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Representative Concentration Pathways (RCP) are
climate change scenario A climate change scenario is a hypothetical future based on a "set of key driving forces".IPCC, 2022Annex I: Glossary an Diemen, R., J.B.R. Matthews, V. Möller, J.S. Fuglestvedt, V. Masson-Delmotte, C.  Méndez, A. Reisinger, S. Semenov (eds) In ...
s to project future
greenhouse gas Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect. T ...
concentrations. These pathways (or ''trajectories'') describe future greenhouse gas concentrations (not emissions) and have been formally adopted by the IPCC. The pathways describe different climate change scenarios, all of which were considered possible depending on the amount of greenhouse gases (GHG) emitted in the years to come. The four RCPs – originally RCP2.6, RCP4.5, RCP6, and RCP8.5 – are labelled after the expected changes in radiative forcing values from the year 1750 to the year 2100 (2.6, 4.5, 6, and 8.5 W/m2, respectively). The IPCC Fifth Assessment Report (AR5) began to use these four pathways for
climate model Numerical climate models (or climate system models) are mathematical models that can simulate the interactions of important drivers of climate. These drivers are the atmosphere, oceans, land surface and ice. Scientists use climate models to st ...
ing and research in 2014. The higher values mean higher greenhouse gas emissions and therefore higher global surface temperatures and more pronounced
effects of climate change Effects of climate change are well documented and growing for Earth's natural environment and human societies. Changes to the climate system include an Instrumental temperature record, overall warming trend, Effects of climate change on the ...
. The lower RCP values, on the other hand, are more desirable for humans but would require more stringent
climate change mitigation Climate change mitigation (or decarbonisation) is action to limit the greenhouse gases in the atmosphere that cause climate change. Climate change mitigation actions include energy conservation, conserving energy and Fossil fuel phase-out, repl ...
efforts to achieve them. In the IPCC's Sixth Assessment Report the original pathways are now being considered together with Shared Socioeconomic Pathways. There are three new RCPs, namely RCP1.9, RCP3.4 and RCP7. A short description of the RCPs is as follows: RCP 1.9 is a pathway that limits
global warming Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...
to below 1.5 °C, the aspirational goal of the
Paris Agreement The Paris Agreement (also called the Paris Accords or Paris Climate Accords) is an international treaty on climate change that was signed in 2016. The treaty covers climate change mitigation, adaptation, and finance. The Paris Agreement was ...
. RCP 2.6 is a ''very stringent'' pathway. RCP 3.4 represents an intermediate pathway between the ''very stringent'' RCP2.6 and less stringent mitigation efforts associated with RCP4.5. RCP 4.5 is described by the IPCC as an ''intermediate scenario''. In RCP 6, emissions peak around 2080, then decline. RCP7 is a ''baseline outcome'' rather than a mitigation target. In RCP 8.5 emissions continue to rise throughout the 21st century. 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. For the extended RCP8.5, global warming of 3.0 to 12.6 °C is projected over the same time period.


Concentrations

The RCPs are consistent with a wide range of possible changes in future anthropogenic (i.e., human)
greenhouse gas emissions Greenhouse gas (GHG) emissions from human activities intensify the greenhouse effect. This contributes to climate change. Carbon dioxide (), from burning fossil fuels such as coal, petroleum, oil, and natural gas, is the main cause of climate chan ...
, and aim to represent their atmospheric concentrations.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
(archive
16 July 2014
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IPCC AR5 WG1
p. 1045–1047
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 The carbon cycle is a part of the biogeochemical cycle where carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Other major biogeochemical cycles include the nitrogen cycle and the water cycl ...
by focusing on concentrations of greenhouse gases, not greenhouse gas inputs. 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 change Land use is an umbrella term to describe what happens on a parcel of land. It concerns the benefits derived from using the land, and also the land management actions that humans carry out there. The following categories are used for land use: for ...
s. 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.


Pathways used in modelling


RCP 1.9

RCP 1.9 is a pathway that limits
global warming Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...
to below 1.5 °C, the aspirational goal of the
Paris Agreement The Paris Agreement (also called the Paris Accords or Paris Climate Accords) is an international treaty on climate change that was signed in 2016. The treaty covers climate change mitigation, adaptation, and finance. The Paris Agreement was ...
.


RCP 2.6

RCP 2.6 is a "very stringent" pathway. According to the IPCC, RCP 2.6 requires that carbon dioxide () emissions start declining by 2020 and go to zero by 2100. It also requires that
methane emissions Increasing methane emissions are a major contributor to the rising concentration of greenhouse gases in Earth's atmosphere, and are responsible for up to one-third of near-term global heating. During 2019, about 60% (360 million tons) of methane r ...
() go to approximately half the levels of 2020, and that sulphur dioxide (SO2) emissions decline to approximately 10% of those of 1980–1990. Like all the other RCPs, RCP 2.6 requires negative emissions (such as absorption by trees). For RCP 2.6, those negative emissions would be on average 2 Gigatons of per year (GtCO2/yr). RCP 2.6 is likely to keep global temperature rise below 2 °C by 2100.


RCP 3.4

RCP 3.4 represents an intermediate pathway between the "very stringent" RCP2.6 and less stringent mitigation efforts associated with RCP4.5. As well as just providing another option a variant of RCP3.4 includes considerable removal of greenhouse gases from the atmosphere.


RCP 4.5

RCP 4.5 is described by the IPCC as an intermediate scenario. Emissions in RCP 4.5 peak around 2040, then decline. According to resource specialists IPCC emission scenarios are biased towards exaggerated availability of
fossil fuels A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geologica ...
reserves; RCP 4.5 is the most probable baseline scenario (no climate policies) taking into account the exhaustible character of non-renewable fuels. According to the IPCC, RCP 4.5 requires that carbon dioxide () emissions start declining by approximately 2045 to reach roughly half of the levels of 2050 by 2100. It also requires that methane emissions () stop increasing by 2050 and decline somewhat to about 75% of the levels of 2040, and that sulphur dioxide (SO2) emissions decline to approximately 20% of those of 1980–1990. Like all the other RCPs, RCP 4.5 requires negative emissions (such as absorption by trees). For RCP 4.5, those negative emissions would be 2 Gigatons of per year (GtCO2/yr). RCP 4.5 is more likely than not to result in global temperature rise between 2 °C and 3 °C, by 2100 with a mean
sea level rise The sea level has been rising from the end of the last ice age, which was around 20,000 years ago. Between 1901 and 2018, the average sea level rose by , with an increase of per year since the 1970s. This was faster than the sea level had e ...
35% higher than that of RCP 2.6. Many plant and animal species will be unable to adapt to the effects of RCP 4.5 and higher RCPs.


RCP 6

In RCP 6, emissions peak around 2080, then decline. The RCP 6.0 scenario uses a high greenhouse gas emission rate and is a stabilisation scenario where total radiative forcing is stabilised after 2100 by employment of a range of technologies and strategies for reducing greenhouse gas emissions. 6.0 W/m2 refers to the radiative forcing reached by 2100. Projections for temperature according to RCP 6.0 include continuous global warming through 2100 where CO2 levels rise to 670 ppm by 2100 making the global temperature rise by about 3–4 °C by 2100.


RCP 7

RCP7 is a baseline outcome rather than a mitigation target.


RCP 8.5

In RCP 8.5 emissions continue to rise throughout the 21st century. RCP8.5 is generally taken as the basis for worst-case climate change scenarios. Since the publication of the
IPCC Fifth Assessment Report The Fifth Assessment Report (AR5) of the United Nations Intergovernmental Panel on Climate Change (IPCC) is the fifth in IPCC#Assessment reports, a series of such reports and was completed in 2014.IPCC (2014The IPCC's Fifth Assessment Report (A ...
(2014) the likelihood of this RCP has been debated, due to overestimation of projected coal outputs. On the other hand, many uncertainties remain on
carbon cycle The carbon cycle is a part of the biogeochemical cycle where carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Other major biogeochemical cycles include the nitrogen cycle and the water cycl ...
feedbacks, which could lead to warmer temperatures than projected in representative concentration pathways. RCP 8.5 is still used for predicting mid-century (and earlier) emissions based on current and stated policies.


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. IPCC: Table SPM-2, in
Summary for Policymakers
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16 July 2014
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IPCC AR5 WG1
/ref> Across all RCPs, global mean temperature is projected to rise by 0.4 to 2.6°C (1.5°C) by the mid 21st century and by 0.3 to 4.8°C (2.55°C) by the late 21st century. According to a 2021 study in which plausible AR5 and RCP scenarios of emissions are selected, Across all RCPs, the global temperature will reach 3°C to 3.25°C above pre-industrial levels in 2100. Across all RCPs, global mean sea level is projected to rise by 0.17 to 0.38 meters (0.275 meters) by the mid 21st century and by 0.26 to 0.82 meters (0.54 meters) by the late 21st century.


23rd century

The
IPCC Fifth Assessment Report The Fifth Assessment Report (AR5) of the United Nations Intergovernmental Panel on Climate Change (IPCC) is the fifth in IPCC#Assessment reports, a series of such reports and was completed in 2014.IPCC (2014The IPCC's Fifth Assessment Report (A ...
also projected changes in climate beyond the 21st century. The extended RCP2.6 pathway assumes sustained net negative anthropogenic GHG emissions after the year 2070. ''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. 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. Between these RCPs, atmospheric CO2 concentrations reach around 1180 ppmv by the late 23rd century. For the extended RCP2.6 scenario, global warming of 0.0 to 1.2°C (0.6°C) is projected for the late 23rd century (2281–2300 average), relative to 1986–2005.Collins, Matthew, ''et al.'': Executive summary, in
Chapter 12: Long-term Climate Change: Projections, Commitments and Irreversibility
(archive
16 July 2014
, i
IPCC AR5 WG1
p. 1033
For the extended RCP8.5, global warming of 3.0 to 12.6°C (7.8°C) is projected over the same time period. Between these RCPs, global warming of 1.5 to 6.9°C (4.2°C) is projected for the late 23rd century (2281-2300 average).


See also

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References


External links


Special Issue: The representative concentration pathways: an overview, ''Climatic Change'', Volume 109, Issue 1–2, November 2011
Most papers in this issue are freely accessible.
The Guardian: A guide to the IPCC's new RCP emissions pathways
(2013) {{climate change Climate change assessment and attribution Intergovernmental Panel on Climate Change Greenhouse gas emissions