14.4. Future scenarios

To predict the expected changes in climate, global circulation model (GCM) simulations are driven by different emission scenarios. First emission scenarios were produced by IPCC (Intergovernmental Panel on Climate Change) in 1990 (IPCC, 1990). In 1992, IPCC released a new emission scenario set, the so-called IS92 scenario family, which contained 6 different scenarios (Leggett et al., 1992). Due the continuous development of our understanding of possible future greenhouse gas emissions and climate change, IPCC have developed a new scenario set, called SRES (Special Report on Emissions Scenarios – Nakicenovic and Swart, 2000). The next generation of emission scenarios for climate change research and assessment, known as Representative Concentration Pathways (RCPs) (Moss et al, 2010).

14.4.1. SRES scenarios

The SRES scenarios cover a wide range of the main driving forces of future emissions, from demographic to technological and economic developments. Each of four different storyline (namely A1, A2, B1 and B2) assumes a distinctly different direction for future developments (Figure 14.8) and therefore different rates of the expected emissions of greenhouse gases, aerosol particles and other air pollutants.

Figure 14.8: Four different storylines (A1, A2 B1 and B2) of SRES scenarios

The four SRES storylines are the following (after IPCC, 2007):

A1 storyline and scenario family: This storyline describes a future world of very rapid economic growth. World population increases until mid-century and declines thereafter. New and more efficient technologies are introduced rapidly. Regional differences in cultural and social fields are decreased. The A1 scenario family develops into three groups that describe alternative directions of technological change in the energy system, which are the following:

  • A1FI: fossil intensive,

  • A1T: non-fossil energy sources,

  • A1B: balance among all sources.

A2 storyline and scenario family: This storyline describes a very heterogeneous world represented by self-reliance and preservation of local identities. Demographics of each region converge very slowly, resulted a continuously increasing global population in 21th century. Economic development is primarily regionally oriented. The economic growth and technological change are more fragmented and slower than in other storylines.

B1 storyline and scenario family: This storyline describes a convergent world as in the A1 storyline, with the same global population that peaks in mid-century and declines thereafter. At the same time, economy changes rapidly toward a service- and information-based direction, introduced clean and resource-efficient technologies. The emphasis is on global solutions to economic, social, and environmental sustainability, including improved equity, but without additional climate initiatives.

B2 storyline and scenario family: This storyline represents a world in which the emphasis is on local solutions to economic, social, and environmental sustainability. It is a world with continuously increasing global population at a rate lower than A2, intermediate levels of economic development, and less rapid and more diverse technological change than in the B1 and A1 storylines. While the scenario is also oriented toward environmental protection and social equity, it focuses on local and regional levels.

SRES scenarios for carbon dioxide emissions from fossil fuels and indusrty between 1990 and 2100

Figure 14.9: SRES scenarios for carbon dioxide (CO2) emissions from fossil fuels and indusrty between 1990 and 2100 for each (A1, A2, B1 and B2) storylines. Source of data: Nakicenovic and Swart, 2000).

SRES scenarios for carbon dioxide emissions from deforestration between 1990 and 2100

Figure 14.10: SRES scenarios for carbon dioxide (CO2) emissions from deforestration between 1990 and 2100 for each (A1, A2, B1 and B2) storylines. Source of data: Nakicenovic and Swart, 2000).

Expected global emissions of the most important greenhouse gases in each storyline are presented in Figure 14.9 – 14.12. Figure 14.9 and Figure 14.10 show the expected CO2 emissions from fossil fuels and industry, and deforestrations, respectively. Figure 14.11 and Figure 14.12 presents the predicted global emissions of methane and nitrous oxide, respectively.

SRES scenarios for methane emissions between 1990 and 2100

Figure 14.11: SRES scenarios for methane (CH4) emissions between 1990 and 2100 for each (A1, A2, B1 and B2) storylines. Source of data: Nakicenovic and Swart, 2000).

SRES scenarios for nitrous oxide emissions between 1990 and 2100

Figure 14.12: SRES scenarios for nitrous oxide (N2O) emissions between 1990 and 2100 for each (A1, A2, B1 and B2) storylines. Source of data: Nakicenovic and Swart, 2000).

14.4.2. Representative Concentration Pathways (RCPs)

Former scenarios have been used in a linear process, when climate change projections have been carried out based on socioeconomic and emission scenarios (Figure 14.13). In contrast to this sequential form, a parallel process for scenario development (Figure 14.14) were decided by IPCC (Moss et al., 2008). These new generation scenarios have been started to develop in 2007. The parallel approach is initiated with the identification of the so-called RCPs (Representative Concentration Pathways), which should provide better integration, consistency, and consideration of feedbacks, and more time to assess impacts and responses.

Sequential approach to development of global scenarios

Figure 14.13: Sequential approach to development of global scenarios

Parallel approach to development of global scenarios

Figure 14.14: Parallel approach to development of global scenarios

RCPs are referred to as pathways to provide time-dependent projections of atmospheric greenhouse gas (GHG) concentrations based on the projections of radiative forcing. They are representative in that they are one of several different scenarios that have similar radiative forcing and emissions characteristics.

Four RCPs (Table 14.2) are produced from available emission and socioecomic scenarios:

the highest pathway for which radiative forcing reaches >8.5 W m–2 by 2100 and continues to rise for some amount of time; two intermediate “stabilization pathways” in which radiative forcing is stabilized at approximately 6 W m–2 and 4.5 W m–2 after 2100; and one pathway where radiative forcing peaks at approximately 3 W m–2 before 2100 and then declines (Figure 14.15). All these scenarios include time paths for emissions and concentrations of the full suite of greenhouse gases, aerosols and chemically active gases, as well as land use and land cover.

Table 14.2: Representative Concentration Pathways (RCPs), as emission scenarios for IPCC Fifths Assessment Report, AR5 (Moss et al., 2008).

Name

Radiative forcing

CO2 equivalent concentration

Pathways

RCP8.5

>8.5 W m–2

> 1370 ppm (2100)

rising concentration

RCP6.0

~6 W m–2

~ 850 ppm (2100)

at stabilization after 2100

RCP4.5

~4.5 W m–2

~ 650 ppm (2100)

at stabilization after 2100

RCP2.6

~3 W m–2

~ 490 ppm (peak before 2100)

peak before 2100 then decline

Total radiative forcing for different RCPs

Figure 14.5: Total radiative forcing (anthropogenic + natural) for different RCPs (RCP8.5, RCP6, RCP4.5 and RCP3PD) including short term variations due to volcanic forcing in the past and cyclical solar forcing (except at times of stabilization). RCPs: Representative Concentration Pathways; ECPs: Extended Concentration Pathways. Based on Meinhausen et al., 2011. Source of data: http://www.pik-potsdam.de/~mmalte/rcps/

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