Climate scenario - Revision history

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	<onlyinclude>'''Climate scenarios''' are plausible representations of the ''future'' [[climate]] of the Earth, based on its current observed state and different [[greenhouse gas]] [[emission scenario]]s.</onlyinclude><ref name=IPCC_SREX>IPCC, 2012: Glossary of terms. In: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press, Cambridge, UK, and New York, NY, USA, pp. 555-564.</ref> Climate scenarios are useful for investigating potential impacts of anthropogenic climate change. Climate scenarios typically use climate projections, by manipulating model outputs and then combining them with observed climate data. A scenario is any reasonable or probable description of a future state of the world. It is not a forecast ~~however each~~ scenario is one alternative possibility of how the future can unfold. A projection serves as the raw material for a scenario, but scenarios require additional information.		<onlyinclude>'''Climate scenarios''' are plausible representations of the ''future'' [[climate]] of the Earth, based on its current observed state and different [[greenhouse gas]] [[emission scenario]]s.</onlyinclude><ref name=IPCC_SREX>IPCC, 2012: Glossary of terms. In: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press, Cambridge, UK, and New York, NY, USA, pp. 555-564.</ref> Climate scenarios are useful for investigating potential impacts of anthropogenic climate change. Climate scenarios typically use climate projections, by manipulating model outputs and then combining them with observed climate data. A scenario is any reasonable or probable description of a future state of the world. However, it is not a forecast. Each scenario is one alternative possibility of how the future can unfold. A projection serves as the raw material for a scenario, but scenarios require additional information.

	Greenhouse gas (GHG) [[emissions]] are the product of complex systems, with exact future emissions nearly impossible to determine. Thus different [[scenario]]s are taken into account, each leading to different effects on the climate. This page discusses these effects; for more information on the exact scenarios, please see [[emission scenario]]s.		Greenhouse gas (GHG) [[emissions]] are the product of complex systems, with exact future emissions nearly impossible to determine. Thus different [[scenario]]s are taken into account, each leading to different effects on the climate. The effects of different emission pathways are also subjected to [[positive climate feedback\|compounding effects]], which lead to faster changes on the climate system. This page discusses these effects; for more information on the exact scenarios, please see [[emission scenario]]s.

	==Climate scenarios from RCPs==		==Climate scenarios from RCPs==
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	==References==		==References==
	{{reflist}}		{{reflist}}
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	<onlyinclude>'''Climate scenarios''' are plausible representations of the ''future'' [[climate]] of the Earth, based on its current observed state and different [[greenhouse gas]] [[emission scenario]]s.</onlyinclude><ref name=IPCC_SREX>IPCC, 2012: Glossary of terms. In: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press, Cambridge, UK, and New York, NY, USA, pp. 555-564.</ref> Climate scenarios are useful for investigating potential impacts of anthropogenic climate change. Climate scenarios typically use climate projections, by manipulating model outputs and then combining them with observed climate data. A scenario is any reasonable or probable description of a future state of the world. It is not a forecast however each scenario is one alternative possibility of how the future can unfold. A projection serves as the raw material for a scenario, but scenarios require additional information.		<onlyinclude>'''Climate scenarios''' are plausible representations of the ''future'' [[climate]] of the Earth, based on its current observed state and different [[greenhouse gas]] [[emission scenario]]s.</onlyinclude><ref name=IPCC_SREX>IPCC, 2012: Glossary of terms. In: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press, Cambridge, UK, and New York, NY, USA, pp. 555-564.</ref> Climate scenarios are useful for investigating potential impacts of anthropogenic climate change. Climate scenarios typically use climate projections, by manipulating model outputs and then combining them with observed climate data. A scenario is any reasonable or probable description of a future state of the world. It is not a forecast however each scenario is one alternative possibility of how the future can unfold. A projection serves as the raw material for a scenario, but scenarios require additional information.

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	''Under RCP8.5'': Changes in [[precipitation]] will vary drastically for different regions around the Earth. High latitudes and the equatorial Pacific are likely to experience an increase in average annual precipitation in the RCP8.5 scenario. In many mid-latitude and subtropical dry locations, average annual precipitation is likely to ''decrease'', while it is expected to ''increase'' in mid-latitude wet regions.<Ref name=ar5/>		''Under RCP8.5'': Changes in [[precipitation]] will vary drastically for different regions around the Earth. High latitudes and the equatorial Pacific are likely to experience an increase in average annual precipitation in the RCP8.5 scenario. In many mid-latitude and subtropical dry locations, average annual precipitation is likely to ''decrease'', while it is expected to ''increase'' in mid-latitude wet regions.<Ref name=ar5/>

	[[Weather#Extreme Weather\|Extreme weather events]] are very likely to increase in both frequency and intensity as global surface temperatures increase. In all RCPs [[monsoon]]s are likely to intensify, as well as [[El ~~nino~~\|El Niño]] related precipitation variability.<Ref name=ar5/>		[[Weather#Extreme Weather\|Extreme weather events]] are very likely to increase in both frequency and intensity as global surface temperatures increase. In all RCPs [[monsoon]]s are likely to intensify, as well as [[El Nino\|El Niño]] related precipitation variability.<Ref name=ar5/>

	===Ocean, cryosphere and sea level===		===Ocean, cryosphere and sea level===

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[[Category:Done 2016-04-30]]
<onlyinclude>'''Climate scenarios''' are plausible representations of the ''future'' [[climate]] of the Earth, based on its current observed state and different [[greenhouse gas]] [[emission scenario]]s.</onlyinclude><ref name=IPCC_SREX>IPCC, 2012: Glossary of terms. In: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press, Cambridge, UK, and New York, NY, USA, pp. 555-564.</ref> Climate scenarios are useful for investigating potential impacts of anthropogenic climate change. Climate scenarios typically use climate projections, by manipulating model outputs and then combining them with observed climate data. A scenario is any reasonable or probable description of a future state of the world. It is not a forecast however each scenario is one alternative possibility of how the future can unfold. A projection serves as the raw material for a scenario, but scenarios require additional information.

Greenhouse gas (GHG) [[emissions]] are the product of complex systems, with exact future emissions nearly impossible to determine. Thus different [[scenario]]s are taken into account, each leading to different effects on the climate. This page discusses these effects; for more information on the exact scenarios, please see [[emission scenario]]s.

==Climate scenarios from RCPs==

Representative Concentration Pathways (RCPs) are the approach taken towards emission scenarios by the [[IPCC]] in their 2014 [[climate change]] [https://www.ipcc.ch/pdf/assessment-report/ar5/syr/SYR_AR5_FINAL_full.pdf report]. There are 4 pathways each with varying emissions of greenhouse gases up until the year 2100. The effects of these will be discussed here.

The 4 pathways are (shown below):
*'''RCP8.5''' - The high emissions pathway, reaching 8.5 [[watt|W]]/[[meter|m]]2 of [[radiative forcing]] by 2100.
*'''RCP6''' - An intermediate pathway, reaching 6 W/m2 by 2100.
*'''RCP4.5''' - An intermediate pathway, reaching 4.5 W/m2 by 2100.
*'''RCP2.6''' - The low emissions pathway, peaking around 3 W/m2 and then declining to 2.6 W/m2 by 2100.

[[File:RCPs_Fig.jpg|300px|thumb|center|Figure 1. Radiative Forcing of the Representative Concentration Pathways. From van Vuuren et al (2011) The Representative Concentration Pathways: An Overview. Climatic Change, 109 (1-2), 5-31. The light grey area captures 98% of the range in previous IAM scenarios, and dark grey represents 90% of the range.<ref>IPCC. (Accessed June 2, 2016). ''Representative Concentration Pathways (RCPs)'' [Online], Available: http://sedac.ipcc-data.org/ddc/ar5_scenario_process/RCPs.html</ref>]]

===Global surface temperature===
''General results'': Under all emission scenarios, the [[temperature of the Earth]] is projected to rise. The Arctic region will warm more rapidly than the global mean temperature, reported with very high [[confidence]]. Warming over land will also occur faster than over ocean, and will exceed the mean global temperature. It is also nearly certain that there will be an [[increasing frequency of warm days and nights]].<ref name=ar5>IPCC. (Accessed June 2, 2016). ''AR5 Climate Change 2014 Synthesis Report'' sec. 2.2, pp.74 [Online], Available: https://www.ipcc.ch/pdf/assessment-report/ar5/syr/SYR_AR5_FINAL_full.pdf#74</ref> It is also very [[likelihood|likely]] that [[heat wave]]s will increase in both frequency and intensity in many regions.

The global mean surface [[temperature]] is expected to change similarly for all 4 pathways up until the year 2035, and will likely be in the range of 0.3 - 0.7°C (relative to 2005), assuming no major disruptions in the [[natural carbon cycle]] such as a large volcanic eruption.<ref name=ar5/> After 2035 however, the pathways begin to diverge up until the year 2100.

Relative to years 1850-1900, the surface temperature change is projected to likely exceed 1.5°C by 2100 for RPC4.5, RPC6 and RPC8.5. It is even likely to exceed 2°C for the RPC6 and RPC8.5 emission scenarios, however this is ''less'' likely for the RPC4.5 and ''unlikely'' for RPC2.6.

===Water cycle===
''Under RCP8.5'': Changes in [[precipitation]] will vary drastically for different regions around the Earth. High latitudes and the equatorial Pacific are likely to experience an increase in average annual precipitation in the RCP8.5 scenario. In many mid-latitude and subtropical dry locations, average annual precipitation is likely to ''decrease'', while it is expected to ''increase'' in mid-latitude wet regions.<Ref name=ar5/>

[[Weather#Extreme Weather|Extreme weather events]] are very likely to increase in both frequency and intensity as global surface temperatures increase. In all RCPs [[monsoon]]s are likely to intensify, as well as [[El nino|El Niño]] related precipitation variability.<Ref name=ar5/>

===Ocean, cryosphere and sea level===
The global [[ocean]] will continue to warm during the 21st century, for all scenarios. Reductions in [[Arctic sea ice]] are also projected for all scenarios. For the RPC8.5 scenario however, the Arctic is projected to be ice-free in the month of September by mid-century.<Ref name=ar5/>

Northern hemisphere snow cover is projected to decrease by 7% for RCP2.6 and by 25% for RCP8.5 by the end of the 21st century. The global [[glacier]] volume is projected to decrease by 15-55% for RCP2.6 and by 35-85% for RCP8.5.<ref name=ar5/>

Mean sea level will continue to [[rising sea level|rise]] during the 21st century, surpassing the recently observed rate of 2 mm/yr (1971-2010) with the RCP8.5 reaching a rate of 8-16 mm/yr during 2081-2100.<Ref name=ar5/> See Figure 1 below for the comparison between RCP2.6 and RCP8.5.

[[File:AR5_SYR_Figure_2.2.png|700px|thumb|center|Figure 2. Coupled Model Intercomparison Project Phase 5 (CMIP5) multi-model mean projections (i.e., the average of the model projections available) for the 2081–2100 period under the RCP2.6 (left) and RCP8.5 (right) scenarios for (a) change in annual mean surface temperature and (b) change in annual mean precipitation, in percentages, and (c) change in average sea level. Changes are shown relative to the 1986–2005 period. The number of CMIP5 models used to calculate the multi-model mean is indicated in the upper right corner of each panel. Stippling (dots) on (a) and (b) indicates regions where the projected change is large compared to natural internal variability (i.e., greater than two standard deviations of internal variability in 20-year means) and where 90% of the models agree on the sign of change. Hatching (diagonal lines) on (a) and (b) shows regions where the projected change is less than one standard deviation of natural internal variability in 20-year means.<Ref name=ar5/>]]

==References==
{{reflist}}