Climate change scenario
A climate change scenario is a hypothetical future based on a "set of key driving forces".[1]: 1812 Scenarios explore the long-term effectiveness of mitigation and adaptation.[2] Scenarios help to understand what the future may hold. They can show which decisions will have the most meaningful effects on mitigation and adaptation.
Closely related to climate change scenarios are pathways, which are more concrete and action-oriented. However, in the literature, the terms scenarios and pathways are often used in a way that they mean the same thing.[3]: 9
Many parameters influence climate change scenarios. Three important parameters are the number of people (and population growth), their economic activity new technologies. Economic and energy models, such as World3 and POLES, quantify the effects of these parameters.
Climate change scenarios exist at a national, regional or global scale. Countries use scenario studies in order to better understand their decisions. This is useful when they are developing their adaptation plans or
Terminology
The IPCC Sixth Assessment Report defines scenario as follows: "A plausible description of how the future may develop based on a [...] set of assumptions about key driving forces and relationships."[7]: 1812 A set of scenarios shows a range of possible futures.
Scenarios are not predictions.[7]: 1812 Scenarios help decision makers to understand what will be the effects of a decision.
The concept of pathways is closely related. The formal definition of pathways is as follows: "The temporal evolution of natural and/or human systems towards a future state. [...] Pathway approaches [...] involve various dynamics, goals, and actors across different scales."[7]: 1810
In other words: pathways are a roadmap which list actions that need to be taken to make a scenario come true. Decision makers can use a pathway to make a plan, e.g. with regards to the timing of fossil-fuel phase out or the reduction of fossil fuel subsidies.
Pathways are more concrete and action-oriented compared to scenarios. They provide a roadmap for achieving desired climate targets. There can be several pathways to achieve the same scenario end point in future.
In the literature the terms scenarios and pathways and often used in a way that they mean the same thing.[8]: 9 The IPCC publications on the physical science basis tend to use scenarios more, whereas the publications on mitigation tend to use modelled emission and mitigation pathways as a term.[8]: 9
Types
There are the following types of scenarios:[1]: 1813
- baseline scenarios
- concentrations scenarios
- emissions scenarios
- mitigation scenarios
- reference scenarios
- socio economic scenarios.
A baseline scenario is used as a reference for comparison against an alternative scenario, e.g., a mitigation scenario.[9] A wide range of quantitative projections of greenhouse gas emissions have been produced.[10] The "SRES" scenarios are "baseline" emissions scenarios (i.e., they assume that no future efforts are made to limit emissions),[11] and have been frequently used in the scientific literature (see Special Report on Emissions Scenarios for details).
Purpose
Climate change scenarios can be thought of as stories of possible futures. They allow the description of factors that are difficult to quantify, such as governance, social structures, and institutions. There is considerable variety among scenarios, ranging from variants of sustainable development, to the collapse of social, economic, and environmental systems.[12]
Factors affecting future GHG emissions
Factors affecting the emission projections include:
- Population projections: All other factors being equal, lower population projections result in lower emissions projections.
- Economic development: Economic activity is a dominant driver of energy demand and thus of GHG emissions.
- Energy use: Future changes in energy systems are a fundamental determinant of future GHG emissions.
- Energy intensity: This is the total primary energy supply (TPES) per unit of GDP.[13] In all of the baseline scenarios assessments, energy intensity was projected to improve significantly over the 21st century. The uncertainty range in projected energy intensity was large.[14]
- Carbon intensity: This is the CO2 emissions per unit of TPES. Compared with other scenarios, Fisher et al. (2007) found that the carbon intensity was more constant in scenarios where no climate policy had been assumed.[14] The uncertainty range in projected carbon intensity was large. At the high end of the range, some scenarios contained the projection that energy technologies without CO2 emissions would become competitive without climate policy. These projections were based on the assumption of increasing fossil fuel prices and rapid technological progress in carbon-free technologies. Scenarios with a low improvement in carbon intensity coincided with scenarios that had a large fossil fuel base, less resistance to coal consumption, or lower technology development rates for fossil-free technologies.
- ]
In producing scenarios, an important consideration is how social and economic development will progress in developing countries.[14] If, for example, developing countries were to follow a development pathway similar to the current industrialized countries, it could lead to a very large increase in emissions. Emissions do not only depend on the growth rate of the economy. Other factors include the structural changes in the production system, technological patterns in sectors such as energy, geographical distribution of human settlements and urban structures (this affects, for example, transportation requirements), consumption patterns (e.g., housing patterns, leisure activities, etc.), and trade patterns the degree of protectionism and the creation of regional trading blocks can affect availability to technology.
In the majority of studies, the following relationships were found (but are not proof of causation):[12]
- Rising GHGs: This was associated with scenarios having a growing, post-industrial economy with globalization, mostly with low government intervention and generally high levels of competition. Income equality declined within nations, but there was no clear pattern in social equity or international income equality.
- Falling GHGs: In some of these scenarios, GDP rose. Other scenarios showed economic activity limited at an ecologicallysustainable level. Scenarios with falling emissions had a high level of government intervention in the economy. The majority of scenarios showed increased social equity and income equality within and among nations.
Predicted trends for greenhouse gas emissions are shown in different formats:
Mitigation scenarios
A typical mitigation scenario is constructed by selecting a long-range target, such as a desired atmospheric concentration of carbon dioxide (CO2), and then fitting the actions to the target, for example by placing a cap on net global and national emissions of greenhouse gases.
An increase of global temperature by more than 2
Concentration scenarios
450 ppm
The BLUE scenarios in the IEA's
World Energy Outlook 2008, mentioned above, also describes a "450 Policy Scenario", in which extra energy investments to 2030 amount to
550 ppm
This is the target advocated (as an upper bound) in the
The
Commonly used pathway descriptions
Closely related to climate change scenarios are pathways, which are more concrete and action-oriented.
The IPCC assessment reports talk about the following types of pathways:[1]: 1810
- 1.5°C pathway
- Adaptation pathways
- Climate-resilient pathways
- Development pathways
- Emission pathways
- Mitigation pathways
- Non-overshoot pathways
- Overshoot pathways
- Representative Concentration Pathways (RCPs)
- Shared Socio-economic Pathways (SSPs)
- Transformation pathways
Representative Concentration Pathway
Representative Concentration Pathways (RCP) are climate change scenarios to project future greenhouse gas 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 a possible range of radiative forcing values in the year 2100 (2.6, 4.5, 6, and 8.5 W/m2, respectively).[23][24][25] The IPCC Fifth Assessment Report (AR5) began to use these four pathways for climate modeling 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. The lower RCP values, on the other hand, are more desirable for humans but would require more stringent climate change mitigation efforts to achieve them.
In the IPCC's
Shared Socioeconomic Pathways
Shared Socioeconomic Pathways (SSPs) are climate change scenarios of projected socioeconomic global changes up to 2100 as defined in the IPCC Sixth Assessment Report on climate change in 2021.[33] They are used to derive greenhouse gas emissions scenarios with different climate policies.[34][35][36] The SSPs provide narratives describing alternative socio-economic developments. These storylines are a qualitative description of logic relating elements of the narratives to each other.[34] In terms of quantitative elements, they provide data accompanying the scenarios on national population, urbanization and GDP (per capita).[37] The SSPs can be quantified with various Integrated Assessment Models (IAMs) to explore possible future pathways both with regards to socioeconomic and climate pathways.[35][36][37]
The five scenarios are:
- SSP1: Sustainability ("Taking the Green Road")
- SSP2: "Middle of the Road"
- SSP3: Regional Rivalry ("A Rocky Road")
- SSP4: Inequality ("A Road Divided")
- SSP5: Fossil-fueled Development ("Taking the Highway") [38]
National climate (change) projections
National climate (change) projections (also termed "national climate scenarios" or "national climate assessments") are specialized regional climate projections, typically produced for and by individual
Typically distributed as a single product, climate projections condense information from multiple
National climate projections form the basis of national climate adaptation and
Design
To explore a wide range of plausible climatic outcomes and to enhance confidence in the projections, national climate change projections are often generated from multiple general circulation models (GCMs). Such climate ensembles can take the form of perturbed physics ensembles (PPE), multi-model ensembles (MME), or initial condition ensembles (ICE).[39] As the spatial resolution of the underlying GCMs is typically quite coarse, the projections are often downscaled, either dynamically using regional climate models (RCMs), or statistically. Some projections include data from areas which are larger than the national boundaries, e.g. to more fully evaluate catchment areas of transboundary rivers. Some countries have also produced more localized projections for smaller administrative areas, e.g. States in the United States, and Länder in Germany.
Various countries have produced their national climate projections with feedback and/or interaction with stakeholders.[40] Such engagement efforts have helped tailoring the climate information to the stakeholders' needs, including the provision of sector-specific climate indicators such as degree-heating days.
Working predictive models
Over 30 countries have reported national climate projections / scenarios in their most recent submissions to the United Nations Framework Convention on Climate Change. Many European governments have also funded national information portals on climate change.[41]
- Australia: CCIA[42]
- California: Cal-Adapt[43]
- Netherlands: KNMI'14[44]
- Switzerland: CH2011[45] / CH2018[46]
For countries which lack adequate resources to develop their own climate change projections, organisations such as
See also
References
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- ^ IPCC, 2023: Summary for Policymakers. In: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland, pp. 1-34, doi: 10.59327/IPCC/AR6-9789291691647.001
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- ^ a b IPCC, 2023: Summary for Policymakers. In: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland, pp. 1-34, doi: 10.59327/IPCC/AR6-9789291691647.001
- ^ IPCC (2007c). "Annex. In: Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz et al. Eds.]". Cambridge University Press, Cambridge, U.K., and New York, N.Y., U.S.A. Archived from the original on 2018-10-05. Retrieved 2009-05-20.
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- ^ Meinshausen, M., Nicholls, Z. R. J., Lewis, J., Gidden, M. J., Vogel, E., Freund, M., Beyerle, U., Gessner, C., Nauels, A., Bauer, N., Canadell, J. G., Daniel, J. S., John, A., Krummel, P. B., Luderer, G., Meinshausen, N., Montzka, S. A., Rayner, P. J., Reimann, S., . . . Wang, R. H. J. (2020). The shared socio-economic pathway (SSP) greenhouse gas concentrations and their extensions to 2500. Geoscientific Model Development, 13(8), 3571–3605. https://doi.org/10.5194/gmd-13-3571-2020 Archived 2023-04-16 at the Wayback Machine
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- ^ a b "SSP Database". tntcat.iiasa.ac.at. Archived from the original on 2020-04-25. Retrieved 2019-11-09.
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Füssel, Hans-Martin (2014). How Is Uncertainty Addressed in the Knowledge Base for National Adaptation Planning?. In Adapting to an Uncertain Climate. pp. 41-66: Springer, Cham. ISBN 978-3-319-04875-8.)
{{cite book}}
: CS1 maint: location (link - ^ Climate Change in Australia
- ^ California climate change scenarios and climate impact research
- ^ KNMI'14 Pictures of the future - Climate scenarios
- ^ "Swiss Climate Change Scenarios CH2011 B". ch2011.ch. Retrieved 2018-08-23.
- ^ CH2018 - New Climate Scenarios for Switzerland
- ^ UKCP18 Project announcement
- ^ UKCP18 Demonstration Projects (Met Office)
- ^ UNDP - Supporting Integrated Climate Change Strategies
- ^ UNFCCC - National Adaptation Programmes of Action - Introduction
External links
- UNDP Climate Change Country Profiles - Introduction;UNDP Climate Change Country Profiles (61 countries)
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