17:15 〜 18:45
[ACG46-P02] CMIP6モデルアンサンブルを用いた影響評価研究を行う際に重要な２つの注意点
キーワード：気候変動、不確実性低減、影響評価、エアロゾル
Here we introduce two crucial issues in impact studies using the CMIP6 ensemble. The first issue is the ‘hot model’ problem. Because some climate models of CMIP6 (‘hot models’) were suggested to overestimate future global warming, the IPCC AR6 used the ‘assessed warming range’ instead of that in the raw ensemble. However, it is not clear how this advance in climate science can contribute to reducing climate-related uncertainties in impact assessments. Here, we show that the climate-related uncertainty of the economic impact of climate change in the world can be observationally constrained (31% of variance can be reduced under RCP4.5 or SSP2-4.5).
The second issue is the ‘distinctiveness’ of SSP3-7.0. Because recent mitigation efforts have made high GHG emissions of SSP5-8.5 highly unlikely, SSP3-7.0 has received attention as an alternative high-end scenario for impact studies. However, the ‘distinctiveness’ of SSP3-7.0 may not be well-recognized by the impact community. Aerosol emissions increase or change little in SSP3-7.0 due to the assumption of a lenient air quality policy, while they decrease in the other SSP-RCPs of CMIP6 and all the RCPs of CMIP5. Here, we show that large aerosol emissions in SSP3-7.0 significantly suppress future increases in precipitation. We recommend impact researchers to compare impact simulations at the same warming level between SSP3-7.0 and SSP5-8.5 to examine the effects of aerosols in the case that such analyses are adequate. We also recommend ScenarioMIP for CMIP7 to exclude scenarios with extreme policies of aerosols (and land-use land-cover changes) from Tier 1 experiments and instead including them in Tier 2.
References:
Shiogama et al. (2022), Nature, https://doi.org/10.1038/s41586-021-04310-8
Shiogama et al. (2022), ERL, https://doi.org/10.1088/1748-9326/aca68d
Shiogama et al. (2023), Nature Clim. Chang, https://doi.org/10.1038/s41558-023-01883-2
The second issue is the ‘distinctiveness’ of SSP3-7.0. Because recent mitigation efforts have made high GHG emissions of SSP5-8.5 highly unlikely, SSP3-7.0 has received attention as an alternative high-end scenario for impact studies. However, the ‘distinctiveness’ of SSP3-7.0 may not be well-recognized by the impact community. Aerosol emissions increase or change little in SSP3-7.0 due to the assumption of a lenient air quality policy, while they decrease in the other SSP-RCPs of CMIP6 and all the RCPs of CMIP5. Here, we show that large aerosol emissions in SSP3-7.0 significantly suppress future increases in precipitation. We recommend impact researchers to compare impact simulations at the same warming level between SSP3-7.0 and SSP5-8.5 to examine the effects of aerosols in the case that such analyses are adequate. We also recommend ScenarioMIP for CMIP7 to exclude scenarios with extreme policies of aerosols (and land-use land-cover changes) from Tier 1 experiments and instead including them in Tier 2.
References:
Shiogama et al. (2022), Nature, https://doi.org/10.1038/s41586-021-04310-8
Shiogama et al. (2022), ERL, https://doi.org/10.1088/1748-9326/aca68d
Shiogama et al. (2023), Nature Clim. Chang, https://doi.org/10.1038/s41558-023-01883-2