the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 Jun 2024
Modeling 2020 regulatory changes in international shipping emissions helps explain 2023 anomalous warming
Abstract. The summer of 2023 has seen an anomalous increase in temperatures even when considering the ongoing greenhouse-gases driven warming trend. Here we demonstrate that regulatory changes to sulfate emissions from international shipping routes, which resulted in a significant reduction in sulfate particulate released during international shipping starting on January 1 2020, have been a major contributing factor to the monthly surface temperature anomalies during the last year. We do this by including in Community Earth System Model (CESM2) simulations the appropriate changes to emission databases developed for the Climate Model Intercomparison Project version 6 (CMIP6). The aerosol termination effect simulated by the updated CESM2 simulations is consistent with observations of both radiative forcing and surface temperature, manifesting a similar delay as the one observed in observational datasets between the implementation of the emission changes and the anomalous increase in warming. Our findings highlight the importance of considering realistic near-future changes in short-lived climate forcers for future climate projections, such as for CMIP7, for an improved understanding and communication of short-term climatic changes.
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RC1: 'Comment on egusphere-2024-1417', Piers M. Forster, 08 Jul 2024
This paper presents a useful contribution to the attribution of the 2023 high temperature anomaly for the role of shipping emission sulphur reductions. I think it needs some contextualising and some sections rewriting for clarity. See attached comments
- AC1: 'Reply on RC1', Daniele Visioni, 29 Jul 2024
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RC2: 'Comment on egusphere-2024-1417', Anonymous Referee #2, 22 Jul 2024
The authors provide a new perspective on the contribution of reduced shipping sulfate emissions to the anomalous observed warming in 2023. While short-term climate forcers are mostly from continental emission sources, this work focuses on a maritime source. Further explanation is needed to make the attribution analysis more comprehensive and accessible to a broader audience. I have several concerns I would like the authors to consider:
- Temperature response to shipping emission reduction contributes considerably to observed temperature anomaly in 2023 (Fig. 2). Given that the CMIP6 SSP 3-7.0 scenario has been suggested to fail to capture East and South Asian anthropogenic aerosol emissions since 2006 (Zhang et al., 2019; Ramachandran et al., 2020), and has shown to have both local and remote impact (Wang et al., 2021; Xie et al., 2023). CESM2 LENS driven by SSP 3-7.0 underestimates the observed both net short-wave radiative flux and net short-wave minus long-wave radiative flux at the top of atmosphere since 2015 (Fig. 1) and, however, CESM2 LENS seems to capture the observed temperature anomaly in 2022 in Fig.2. Considering the low bias in radiative flux at the top of atmosphere in CESM2 LENS, it suggests other factors, such as internal variability, also contribute. Additionally, Fig. 3 shows anomalous warming in the tropical Pacific resembling an El Niño pattern. I recommend the authors discuss the impact of bias in emission scenarios and the potential impact of other factors.
- The authors estimate an increase in radiative forcing of 0.2 W/m² due to reduced shipping sulfate emissions, and aerosol-cloud interaction plays an important role. This is a significant magnitude, and I would expect a strong surface temperature response. There is no further explanation on how cloud response indirectly contributes to change in radiative forcing. The authors conclude that there is a three-year lag in surface temperature response due to ocean. I recommend showing results starting from 2020 and including the range of ensemble members in Fig 2. Additionally, a spatial map showing the geographic pattern of surface temperature response, as well as full-sky radiative forcing, would be helpful, especially as shipping reductions are most pronounced in the North Atlantic.
- I recommend including one or two more observational datasets or reanalyses to account for uncertainty. As ERA5 has shown bias in capturing observed top-of-atmosphere radiative fluxes, it is unclear why its results are included in the main figure and Fig. A5. The authors should clarify this choice. Additionally, the description of the Berkeley dataset is missing. Providing a brief description in the main text would be beneficial.
Reference
Ramachandran, S., Rupakheti, M. and Lawrence, M.G., 2020. Aerosol-induced atmospheric heating rate decreases over South and East Asia as a result of changing content and composition. Scientific Reports, 10(1), p.20091.
Zhang, Q., Zheng, Y., Tong, D., Shao, M., Wang, S., Zhang, Y., Xu, X., Wang, J., He, H., Liu, W. and Ding, Y., 2019. Drivers of improved PM2. 5 air quality in China from 2013 to 2017. Proceedings of the National Academy of Sciences, 116(49), pp.24463-24469.
Xie, Y., Huang, J., Wu, G., Lei, N. and Liu, Y., 2023. Enhanced Asian warming increases Arctic amplification. Environmental Research Letters, 18(3), p.034041.
Wang, Z., Lin, L., Xu, Y., Che, H., Zhang, X., Zhang, H., Dong, W., Wang, C., Gui, K. and Xie, B., 2021. Incorrect Asian aerosols affecting the attribution and projection of regional climate change in CMIP6 models. npj Climate and Atmospheric Science, 4(1), p.2.
Citation: https://doi.org/10.5194/egusphere-2024-1417-RC2 - AC2: 'Reply on RC2', Daniele Visioni, 29 Jul 2024
Status: closed
-
RC1: 'Comment on egusphere-2024-1417', Piers M. Forster, 08 Jul 2024
This paper presents a useful contribution to the attribution of the 2023 high temperature anomaly for the role of shipping emission sulphur reductions. I think it needs some contextualising and some sections rewriting for clarity. See attached comments
- AC1: 'Reply on RC1', Daniele Visioni, 29 Jul 2024
-
RC2: 'Comment on egusphere-2024-1417', Anonymous Referee #2, 22 Jul 2024
The authors provide a new perspective on the contribution of reduced shipping sulfate emissions to the anomalous observed warming in 2023. While short-term climate forcers are mostly from continental emission sources, this work focuses on a maritime source. Further explanation is needed to make the attribution analysis more comprehensive and accessible to a broader audience. I have several concerns I would like the authors to consider:
- Temperature response to shipping emission reduction contributes considerably to observed temperature anomaly in 2023 (Fig. 2). Given that the CMIP6 SSP 3-7.0 scenario has been suggested to fail to capture East and South Asian anthropogenic aerosol emissions since 2006 (Zhang et al., 2019; Ramachandran et al., 2020), and has shown to have both local and remote impact (Wang et al., 2021; Xie et al., 2023). CESM2 LENS driven by SSP 3-7.0 underestimates the observed both net short-wave radiative flux and net short-wave minus long-wave radiative flux at the top of atmosphere since 2015 (Fig. 1) and, however, CESM2 LENS seems to capture the observed temperature anomaly in 2022 in Fig.2. Considering the low bias in radiative flux at the top of atmosphere in CESM2 LENS, it suggests other factors, such as internal variability, also contribute. Additionally, Fig. 3 shows anomalous warming in the tropical Pacific resembling an El Niño pattern. I recommend the authors discuss the impact of bias in emission scenarios and the potential impact of other factors.
- The authors estimate an increase in radiative forcing of 0.2 W/m² due to reduced shipping sulfate emissions, and aerosol-cloud interaction plays an important role. This is a significant magnitude, and I would expect a strong surface temperature response. There is no further explanation on how cloud response indirectly contributes to change in radiative forcing. The authors conclude that there is a three-year lag in surface temperature response due to ocean. I recommend showing results starting from 2020 and including the range of ensemble members in Fig 2. Additionally, a spatial map showing the geographic pattern of surface temperature response, as well as full-sky radiative forcing, would be helpful, especially as shipping reductions are most pronounced in the North Atlantic.
- I recommend including one or two more observational datasets or reanalyses to account for uncertainty. As ERA5 has shown bias in capturing observed top-of-atmosphere radiative fluxes, it is unclear why its results are included in the main figure and Fig. A5. The authors should clarify this choice. Additionally, the description of the Berkeley dataset is missing. Providing a brief description in the main text would be beneficial.
Reference
Ramachandran, S., Rupakheti, M. and Lawrence, M.G., 2020. Aerosol-induced atmospheric heating rate decreases over South and East Asia as a result of changing content and composition. Scientific Reports, 10(1), p.20091.
Zhang, Q., Zheng, Y., Tong, D., Shao, M., Wang, S., Zhang, Y., Xu, X., Wang, J., He, H., Liu, W. and Ding, Y., 2019. Drivers of improved PM2. 5 air quality in China from 2013 to 2017. Proceedings of the National Academy of Sciences, 116(49), pp.24463-24469.
Xie, Y., Huang, J., Wu, G., Lei, N. and Liu, Y., 2023. Enhanced Asian warming increases Arctic amplification. Environmental Research Letters, 18(3), p.034041.
Wang, Z., Lin, L., Xu, Y., Che, H., Zhang, X., Zhang, H., Dong, W., Wang, C., Gui, K. and Xie, B., 2021. Incorrect Asian aerosols affecting the attribution and projection of regional climate change in CMIP6 models. npj Climate and Atmospheric Science, 4(1), p.2.
Citation: https://doi.org/10.5194/egusphere-2024-1417-RC2 - AC2: 'Reply on RC2', Daniele Visioni, 29 Jul 2024
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