Climate change scenario

Short description: Projections of future greenhouse gas emissions

There are different future climate change scenarios (here shown in terms of global temperatures, on the right), depending on the amount of greenhouse gases emitted and pledges made under the Paris Agreement (on the left); data from 2015.[1][2]

Climate change scenarios or socioeconomic scenarios are projections of future greenhouse gas (GHG) emissions used by analysts to assess future vulnerability to climate change.[3] Scenarios and pathways are created by scientists[4] to survey any long term routes and explore the effectiveness of mitigation and helps us understand what the future may hold. This will allow us to envision the future of human environment system.[4] Producing scenarios requires estimates of future population levels, economic activity, the structure of governance, social values, and patterns of technological change. Economic and energy modelling (such as the World3 or the POLES models) can be used to analyze and quantify the effects of such drivers.

Scientists can develop separate international, regional and national climate change scenarios. These scenarios are designed to help stakeholders understand what kinds of decisions will have meaningful effects on climate change mitigation or adaptation. Most countries developing adaptation plans or Nationally Determined Contributions will commission scenario studies in order to better understand the decisions available to them.

International goals for mitigating climate change through international processes like the Paris Agreement are based on reviews of these scenarios. For example, the Special Report on Global Warming of 1.5 °C was released in 2018 order to reflect more up-to-date models of emissions, Nationally Determined Contributions, and impacts of climate change than its predecessor IPCC Fifth Assessment Report published in 2014 before the Paris Agreement.[5]

## Contents

* 1 Purpose
* 2 Tools
* 2.1 Shared Socioeconomic Pathways
* 2.2 Representative Concentration Pathway
* 3 Factors affecting future GHG emissions
* 3.1 Stabilization wedges
* 3.2 Target levels of CO2
* 3.2.1 450 ppm
* 3.2.2 550 ppm
* 3.3 Other greenhouse gases
* 3.4 Trends and predictions
* 3.5 Previous predictions
* 3.5.1 UNEP 2011 synthesis report
* 4 National climate (change) projections
* 4.1 Design
* 4.2 Working predictive models
* 5 See also
* 6 References
* 7 External links

## 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.[6]

A baseline scenario is used as a reference for comparison against an alternative scenario, e.g., a mitigation scenario.[7] A wide range of quantitative projections of greenhouse gas emissions have been produced.[8] The "SRES" scenarios are "baseline" emissions scenarios (i.e., they assume that no future efforts are made to limit emissions),[9] and have been frequently used in the scientific literature (see Special Report on Emissions Scenarios for details).

## Tools

### Shared Socioeconomic Pathways

This section is an excerpt from Shared Socioeconomic Pathways[ edit ]

### Representative Concentration Pathway

This section is an excerpt from Representative Concentration Pathway[ edit ]

## Factors affecting future GHG emissions

No strong patterns were found in the relationship between economic activity and GHG emissions. Economic growth was found to be compatible with increasing or decreasing GHG emissions. In the latter case, emissions growth is mediated by increased energy efficiency, shifts to non-fossil energy sources, and/or shifts to a post-industrial (service-based) economy.

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.[10] 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.[11]
* 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.[11] 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.
* Land-use change: Land-use change plays an important role in climate change, impacting on emissions, sequestration and albedo. One of the dominant drivers in land-use change is food demand. Population and economic growth are the most significant drivers of food demand.Cite error: Closing `</ref>` missing for `<ref>` tag

A typical mitigation scenario is constructed by selecting a long-range target, such as a desired atmospheric concentration of carbon dioxide (CO
2), 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 °C has come to be the majority definition of what would constitute intolerably dangerous climate change with efforts to limit the temperature increase to 1.5 °C above pre-industrial levels per the Paris Agreement. Some climate scientists are increasingly of the opinion that the goal should be a complete restoration of the atmosphere's preindustrial condition, on the grounds that too protracted a deviation from those conditions will produce irreversible changes.[citation needed]

### Stabilization wedges

A stabilization wedge is an action which incrementally reduces projected emissions. The name is derived from the triangular shape of the gap between reduced and unreduced emissions trajectories when graphed over time. For example, a reduction in electricity demand due to increased efficiency means that less electricity needs to be generated and thus fewer emissions need to be produced. The term originates in the Stabilization Wedge Game. As a reference unit, a stabilization wedge is equal to the following examples of mitigation initiatives: deployment of two hundred thousand 10 MW wind turbines; completely halting the deforestation and planting of 300 million hectares of trees; the increase in the average energy efficiency of all the world's buildings by 25 percent;[when?] or the installation of carbon capture and storage facilities in 800 large coal-fired power plants.[12] Pacala and Socolow proposed in their work, Stabilization Wedges, that seven wedges are required to be delivered by 2050 – at current technologies – to make a significant impact on the mitigation of climate change.[13] There are, however, sources that estimate the need for 14 wedges because Pacala and Socolow's proposal would only stabilize carbon dioxide emissions at current levels but not the atmospheric concentration, which is increasing by more than 2 ppm/year.[12] In 2011, Socolow revised their earlier estimate to nine.[14]

### Target levels of CO

Carbon budget and emission reduction scenarios needed to reach the two-degree target agreed to in the Paris Agreement (without net negative emissions, based on peak emissions)[15]

Contributions to climate change, whether they cool or warm the Earth, are often described in terms of the radiative forcing or imbalance they introduce to the planet's energy budget. Now and in the future, anthropogenic carbon dioxide is believed to be the major component of this forcing, and the contribution of other components is often quantified in terms of "parts-per-million carbon dioxide equivalent" (ppm CO2e), or the increment/decrement in carbon dioxide concentrations which would create a radiative forcing of the same magnitude.

#### 450 ppm

The BLUE scenarios in the IEA's Energy Technology Perspectives publication of 2008 describe pathways to a long-range concentration of 450 ppm. Joseph Romm has sketched how to achieve this target through the application of 14 wedges.[16]

World Energy Outlook 2008, mentioned above, also describes a "450 Policy Scenario", in which extra energy investments to 2030 amount to United States dollar 9.3 trillion over the Reference Scenario. The scenario also features, after 2020, the participation of major economies such as China and India in a global cap-and-trade scheme initially operating in OECD and European Union countries. Also the less conservative 450 ppm scenario calls for extensive deployment of negative emissions, i.e. the removal of CO
2 from the atmosphere. According to the International Energy Agency (IEA) and OECD, "Achieving lower concentration targets (450 ppm) depends significantly on the use of BECCS".[17]

#### 550 ppm

This is the target advocated (as an upper bound) in the Stern Review. As approximately a doubling of CO
2 levels relative to preindustrial times, it implies a temperature increase of about three degrees, according to conventional estimates of climate sensitivity. Pacala and Socolow list 15 "wedges", any 7 of which in combination should suffice to keep CO
2 levels below 550 ppm.[18]

The International Energy Agency's World Energy Outlook report for 2008 describes a "Reference Scenario" for the world's energy future "which assumes no new government policies beyond those already adopted by mid-2008", and then a "550 Policy Scenario" in which further policies are adopted, a mixture of "cap-and-trade systems, sectoral agreements and national measures". In the Reference Scenario, between 2006 and 2030 the world invests $26.3 trillion in energy-supply infrastructure; in the 550 Policy Scenario, a further $4.1 trillion is spent in this period, mostly on efficiency increases which deliver fuel cost savings of over $7 trillion.[19]

### Other greenhouse gases

Greenhouse gas concentrations are aggregated in terms of carbon dioxide equivalent. Some multi-gas mitigation scenarios have been modeled by Meinshausen et al.[20]

### Trends and predictions

This section is an excerpt from Climate change mitigation#Needed emissions cuts[ edit ]

This section is an excerpt from Climate change mitigation#Pledges[ edit ]

This section is an excerpt from Carbon budget#Recent and currently remaining carbon budget[ edit ]

### Previous predictions

#### UNEP 2011 synthesis report

The United Nations Environment Programme (UNEP, 2011)[21]: 7 looked at how world emissions might develop out to the year 2020 depending on different policy decisions. To produce their report, UNEP (2011)[21]: 8 convened 55 scientists and experts from 28 scientific groups across 15 countries.

Projections, assuming no new efforts to reduce emissions or based on the "business-as-usual" hypothetical trend,[22] suggested global emissions in 2020 of 56 gigatonnes CO2-equivalent (GtCO2-eq), with a range of 55-59 GtCO2-eq.[21]: 12 In adopting a different baseline where the pledges to the Copenhagen Accord were met in their most ambitious form, the projected global emission by 2020 will still reach the 50 gigatonnes CO2.[23] Continuing with the current trend, particularly in the case of low-ambition form, there is an expectation of 3° Celsius temperature increase by the end of the century, which is estimated to bring severe environmental, economic, and social consequences.[24]

The report also considered the effect on emissions of policies put forward by UNFCCC Parties to address climate change. Assuming more stringent efforts to limit emissions lead to projected global emissions in 2020 of between 49 and 52 GtCO2-eq, with a median estimate of 51 GtCO2-eq.[21]: 12 Assuming less stringent efforts to limit emissions lead to projected global emissions in 2020 of between 53 and 57 GtCO2-eq, with a median estimate of 55 GtCO2-eq.[21]: 12

## National climate (change) projections

Further information: Biology:Effects of climate change

National climate (change) projections (also termed "national climate scenarios" or "national climate assessments") are specialized regional climate projections, typically produced for and by individual countries. What distinguishes national climate projections from other climate projections is that they are officially signed off by the national government, thereby being the relevant national basis for adaptation planning. Climate projections are commonly produced over several years by countries' national meteorological services or academic institutions working on climate change.

Typically distributed as a single product, climate projections condense information from multiple climate models, using multiple greenhouse gas emission pathways (e.g. Representative Concentration Pathways) to characterize different yet coherent climate futures. Such a product highlights plausible climatic changes through the use of narratives, graphs, maps, and perhaps raw data. Climate projections are often publicly available for policy-makers, public and private decision makers, as well as researchers to undertake further climate impact studies, risk assessments, and climate change adaptation research. The projections are updated every few years, in order to incorporate new scientific insights and improved climate models.

National climate projections form the basis of national climate adaptation and climate resilience plans, which are reported to UNFCCC and used in IPCC assessments.

### 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).[25] 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.[26] 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.[27]

* Australia : CCIA[28]
* California : Cal-Adapt[29]
* Netherlands: KNMI'14[30]
* Switzerland : CH2011[31] / CH2018[32]
* UK: UKCP09 / UKCP18[33][34]

For countries which lack adequate resources to develop their own climate change projections, organisations such as UNDP or FAO have sponsored development of projections and national adaptation programmes (NAPAs).[35][36]

## See also

* Carbon budget
* CMIP
* Copernicus Programme
* Ensemble forecasting
* Sensitivity analysis
* Uncertainty analysis
* Scenario planning

## References

1. ↑ USGCRP (in en). ﻿Climate Science Special Report﻿ (Report). U.S. Global Change Research Program, Washington, DC. pp. 1–470. https://science2017.globalchange.gov/.
2. ↑ Fawcett, Allen A.; Iyer, Gokul C.; Clarke, Leon E.; Edmonds, James A.; Hultman, Nathan E.; McJeon, Haewon C.; Rogelj, Joeri; Schuler, Reed et al. (2015-12-04). "Can Paris pledges avert severe climate change?" (in en). Science 350 (6265): 1168–1169. doi:10.1126/science.aad5761. ISSN 0036-8075. https://www.science.org/doi/10.1126/science.aad5761.
3. ↑ Carter, T.R. (2001). "Developing and Applying Scenarios. In: Climate Change 2001: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change [J.J. McCarthy et al. Eds."]. Cambridge University Press, Cambridge, U.K., and New York, N.Y., U.S.A.. http://www.ipcc.ch/publications_and_data/publications_and_data_reports.htm.
4. ↑ 4.0 4.1 "IPCC AR6 WG3 Ch3". https://report.ipcc.ch/ar6wg3/pdf/IPCC_AR6_WGIII_FinalDraft_Chapter03.pdf.
5. ↑ ﻿Press release: Special Report on Global Warming of 1.5°C﻿ (Report). Incheon, Republic of Korea: Intergovernmental Panel on Climate Change (IPCC). 8 October 2018. https://www.ipcc.ch/site/assets/uploads/2018/11/pr_181008_P48_spm_en.pdf. Retrieved 7 October 2018.
6. ↑ Morita, T. (2001). "Greenhouse Gas Emission Mitigation Scenarios and Implications. In: Climate Change 2001: Mitigation. Contribution of Working Group III to the Third 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.. http://www.ipcc.ch/publications_and_data/publications_and_data_reports.htm.
7. ↑ 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.. http://www.ipcc.ch/publications_and_data/publications_and_data_reports.htm.
8. ↑ Fisher, "Chapter 3: Issues related to mitigation in the long-term context", Archived copy, Sec. 3.1 Emissions scenarios, http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch3.html, retrieved 2012-09-08 , in IPCC AR4 WG3 (2007)
9. ↑ Morita, "Chapter 2, Greenhouse Gas Emission Mitigation Scenarios and Implications", Archived copy, Sec. 2.5.1.1 IPCC Emissions Scenarios and the SRES Process, http://www.grida.no/climate/ipcc_tar/wg3/068.htm, retrieved 2012-09-08 , in IPCC TAR WG3 (2001).
10. ↑ Rogner, H.-H. (2007). "Introduction. 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.. http://www.ipcc.ch/publications_and_data/publications_and_data_reports.htm.
11. ↑ 11.0 11.1 Fisher, B.S. (2007). "Issues related to mitigation in the long term context. 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.. http://www.ipcc.ch/publications_and_data/publications_and_data_reports.htm.
12. ↑ 12.0 12.1 Dawson, Brian; Spannagle, Matt (2008). The Complete Guide to Climate Change. Oxon: Routledge. pp. 283. ISBN 978-0415477895. https://archive.org/details/completeguidetoc00daws.
13. ↑ Pacala, S.; Socolow, R. (2004-08-13). "Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies" (in en). Science 305 (5686): 968–972. doi:10.1126/science.1100103. ISSN 0036-8075. PMID 15310891. Bibcode: 2004Sci...305..968P.
14. ↑ Socolow, Robert (September 27, 2011). "Wedges reaffirmed - Bulletin of the Atomic Scientists" (in en-US). Bulletin of the Atomic Scientists. https://thebulletin.org/2011/09/wedges-reaffirmed/.
15. ↑ Christiana Figueres; Hans Joachim Schellnhuber; Gail Whiteman; Johan Rockström (2017-06-29). "Three years to safeguard our climate" (in en). Nature 546 (7660): pp. 593–595. doi:10.1038/546593a. ISSN 0028-0836. http://www.nature.com/articles/546593a.
16. ↑ Is 450 ppm (or less) politically possible? Part 2: The Solution
17. ↑ "OECD Environmental Outlook to 2050, Climate Change Chapter, pre-release version". OECD. 2011. http://www.oecd.org/dataoecd/32/53/49082173.pdf.
18. ↑ Pacala, S.; Socolow, R. (13 August 2004). "Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies". Science 305 (5686): 968–972. doi:10.1126/science.1100103. PMID 15310891. Bibcode: 2004Sci...305..968P.
19. ↑ http://www.iea.org/weo/docs/weo2008/fact_sheets_08.pdf World Energy Outlook 2008 Fact Sheet
20. ↑ Meinshausen, M.; Hare, B.; Wigley, T. M. M.; Vuuren, D.; Elzen, M. G. J.; Swart, R. (2006). "Multi-gas Emissions Pathways to Meet Climate Targets". Climatic Change 75 (1–2): 151. doi:10.1007/s10584-005-9013-2. Bibcode: 2006ClCh...75..151M. http://doc.rero.ch/record/319658/files/10584_2005_Article_9013.pdf.
21. ↑ 21.0 21.1 21.2 21.3 21.4 UNEP (November 2011), Bridging the Emissions Gap: A UNEP Synthesis Report, Nairobi, Kenya: United Nations Environment Programme (UNEP), ISBN 978-92-807-3229-0, http://www.unep.org/pdf/UNEP_bridging_gap.pdf, retrieved 2012-09-08 UNEP Stock Number: DEW/1470/NA
22. ↑ Fozzard, Adrian (2014). Climate Change Public Expenditure and Institutional Review Sourcebook (CCPEIR). Washington, D.C.: World Bank Publications. pp. 92.
23. ↑ Alam, Shawkat; Bhuiyan, Jahid; Chowdhury, Tareq; Techera, Erika (2013). Routledge Handbook of International Environmental Law. London: Routledge. pp. 373. ISBN 9780415687171.
24. ↑ Govaere, Inge; Poli, Sara (2014). EU Management of Global Emergencies: Legal Framework for Combating Threats and Crises. Leiden: BRILL Nijhoff. pp. 313. ISBN 9789004268326.
25. ↑ Parker, Wendy S. (2012). "Whose Probabilities? Predicting Climate Change with Ensembles of Models" (in en). Philosophy of Science 77 (5): 985–997. doi:10.1086/656815. ISSN 0031-8248.
26. ↑ Skelton, Maurice; Porter, James J.; Dessai, Suraje; Bresch, David N.; Knutti, Reto (2017-04-26). "The social and scientific values that shape national climate scenarios: a comparison of the Netherlands, Switzerland and the UK" (in en). Regional Environmental Change 17 (8): 2325–2338. doi:10.1007/s10113-017-1155-z. ISSN 1436-3798. PMID 32009852.
27. ↑ 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.
28. ↑ Climate Change in Australia
29. ↑ California climate change scenarios and climate impact research
30. ↑ KNMI'14 Pictures of the future - Climate scenarios
31. ↑ "Swiss Climate Change Scenarios CH2011 B". http://ch2011.ch/en/index.html.
32. ↑ CH2018 - New Climate Scenarios for Switzerland
33. ↑ UKCP18 Project announcement
34. ↑ UKCP18 Demonstration Projects (Met Office)
35. ↑ UNDP - Supporting Integrated Climate Change Strategies
36. ↑ 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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