the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Nov 2023
Aerosol uncertainties in tropical precipitation changes for the mid-Pliocene Warm Period
Abstract. The mid-Pliocene Warm Period (mPWP, 3.3 – 3.0 Ma) was characterised by an atmospheric CO2 concentration exceeding 400 ppmv with minor changes in continental and orbital configurations. Simulations of this past climate state have improved with newer models, but still show some substantial differences from proxy reconstructions. There is little information about atmospheric aerosol concentrations during the Pliocene, but previous work suggests that is could have been quite different from the modern. Here we apply idealised aerosol scenario experiments to examine the importance of aerosol forcing on mPWP tropical precipitation and the possibility of aerosol uncertainty explaining the mismatch between reconstructions and simulations. The absence of industrial pollutants leads to further warming especially in the Northern Hemisphere. The Intertropical Convergence Zone (ITCZ) becomes narrower and stronger and shifts northward after removal of anthropogenic aerosols. Though not affecting the location of monsoon domain boundary, removal of anthropogenic aerosol alters the amount of rainfall within the domain, increasing summer rain rate over eastern and southern Asia and western Africa. This work demonstrates that uncertainty in aerosol forcing could be the dominant driver in tropical precipitation changes during the mid-Pliocene: causing larger impacts than the changes in topography and greenhouse gases.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Interactive discussion
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RC1: 'Comment on egusphere-2023-2702', Anonymous Referee #1, 19 Dec 2023
Zhao et al. apply idealised aerosol scenario experiments to examine the importance of aerosol forcing on mPWP tropical precipitation and the possibility of aerosol uncertainty explaining the mismatch between reconstructions and simulations. Based on these simulations, the authors suggested that i) removal of aerosol pollutants cause global warming and further warms the Northern Hemisphere due to asymmetrical emissions; ii) the Intertropical Convergence Zone (ITCZ) becomes narrower and stronger and shifts northward after removal of anthropogenic aerosols. The content of this manuscript is potentially interesting and there is certainly publishable material in it. However, the manuscript is far from being acceptable to an international journal in its current form, as it has many scientific uncertainties for the reader. Some interpretations are self-contradictory and needs to be untangled. My detailed comments are listed as below.
- Line 51, the authors stated that “mPWP simulations now use modern-day or pre-industrial aerosol concentration that may differ from the conditions during the mPWP. It implies that aerosol effects may be one of the possible explanations for the mismatch between reconstructions and simulations”. However, in the experimental design, the authors also used the modern-day and pre-industrial aerosol concentration, and explained the mismatch between reconstructions and simulations based on these simulations, sinks into logic antinomy.
- The authors explained the spatial pattern of temperature change using asymmetrical emissions. However, the atmosphere is a dynamic collection of gases that constantly move and change, so the aerosols in the atmosphere will distribute globally. How can the aerosols keep asymmetrical distribution? The authors should give more discussion.
- Lines 169-171, these two sentences are contradictory, please check if the description is incorrect. Based on fig. 1a and fig. 5a, I think the mPWP boundary conditions cause more warming than removing anthropogenic aerosols.
- Line 176, the author stated that the ITCZ becomes narrower. However, I think it is really hard to get this conclusion only based on the precipitation changes. The authors should provide more convincing evidence.
- Lines 180-183, the authors stated that “The pattern of the magnitudes of tropical precipitation anomaly matches the tropical temperature warming over oceans”. I am unable to obtain this result from Fig 5. For example, the authors stated that tropical precipitation increases greater over the tropical Pacific and Indian Ocean, however, the temperature changes are similar over the whole tropical oceans.
- Lines 193-197, the sentence “Land regional……cooling effect” is hard to be understood. The first half of the sentence expresses that the monsoon are enhanced, but the second half shows that monsoon are weakened. Please rewrite.
- Lines 218-220, the sentence is self-contradictory. The authors stated Plio_Pristine - Plio_Polluted have relatively small effects on surface wind in the first half of the sentence, then stated that removing anthropogenic aerosols have much stronger effects on surface wind.
Technical corrections
- Please indent the first line of each paragraph, which makes easier for readers to read.
- Replace “0 - 0.8 °C” with “at 0-8 °C”, otherwise, it's hard to distinguish with minus sign. Please check the whole paper and correct it.
- In the Model description, please add some sentences to introduce the relation between the CESM and CCSM4. Moreover, add the full name of CCSM.
- line 175, add reverse parentheses “A2)”.
- Please improve the Figures. For example, i) delete the grid in the figures; ii) In figure 1, the “surface temperature change (℃)” coincided with “(b) PR Plio_Pristine – PI”.
Citation: https://doi.org/10.5194/egusphere-2023-2702-RC1 -
AC1: 'Reply on RC1', Anni Zhao, 09 Jan 2024
We would like to thank you for reviewing our manuscript and providing comments about our work. We are happy to adopt many of the comments and will revise the manuscript as requested.
—Line 51: A brief explanation is that the highlighted sentences say that simulated mPWP climate change does not include aerosol forcing, while our analysis mainly focuses on aerosol effects in mPWP simulations. The first highlighted sentence is trying to say that traditional mPWP simulations usually set prescribed aerosol concentrations same as the control runs, which means that they do not consider aerosol forcings. Our work uses three simulations: a pre-industrial control simulation (PI), a simulation with mPWP boundary condition plus pre-industrial aerosol (Plio_Pristine) and one with mPWP boundary condition plus industrial pollutants (Plio_Polluted). The simulated mPWP change from the highlighted sentence is equivalent to "Plio_Pristine - PI" in our study (Sect. 3.1). We then compares the simulated mPWP change (Plio_Pristine - PI) with the reconstructions in this section, in purpose of firstly evaluating our simulated mPWP climate and secondly pointing out the existence of data-model mismatch. Plio_Pristine - Plio_Polluted considers effects of aerosol forcing in the mPWP simulations (Sect. 3.2 and 3.3). Idealised aerosol scenarios were chosen, because the realistic mPWP aerosol concentrations are not available. Plio_Polluted uses industrial pollutants (Lamarque et al., 2010), which is a real existed aerosol forcing though not happened during the mPWP. Analysis related to aerosol effects does not touch data-model comparison. We will rewrite line 51 to "The discrepancy between mPWP simulations and reconstructions (Haywood et al., 2013, 2020) implies that models might miss some important mechanisms (Fedorov et al., 2013) or prescribed forcing could be a source of uncertainty (Feng et al., 2019). The mPWP simulations now use modern-day or pre-industrial aerosol concentration same as the control runs that may differ from the conditions during mPWP. Lack of including the effect of aerosol forcings and the usage of unrealistic prescribed aerosol concentration in mPWP simulations implies that aerosol effects may be one of the possible explanation for the mismatch between reconstructions and simulations."
—Aerosol distribution: Plio_Pristine and Plio_Polluted simulations in our study use prescribed aerosols, which give aerosol distribution instantaneously at the beginning and then left the model to respond to it. Aerosols do not distribute globally as the lifetime of aerosols is only a few weeks. The atmosphere is not well-mixed and the North-South difference emissions persists into concentrations.
—Lines 169-171: The mPWP boundary conditions cause more warming than removing anthropogenic aerosols. That’s what conclude in line 171 as "...This suggests that changes in boundary conditions are relative more important than aerosol effects in mPWP warming." We are trying to say that removing aerosols only causes more over Northeastern Pacific and high-latitude North Atlantic Ocean than the mPWP boundaries. We will rewrite the sentence to "However, the mPWP boundary conditions causes more warming than removing anthropogenic aerosols nearly global except Northeastern Pacific and high-latitude North Atlantic Ocean (Fig. 5a,c,e). More warming lead by the mPWP boundaries than removal of aerosols suggests ..." to emphasise that the mPWP boundaries lead to more warming than removal of aerosols.
—Line 176: We will add a figure and discussion about changes in the Hadley circulation.
—Lines 180-183: The temperature along the Equator in the Pacific Ocean is greater than surroundings. The warming band is largely overlap with the precipitation increase belt.
—Lines 193-197: The evidence (the citations in sentences) in the second half says that the cooling effect induced by in- creased aerosol during 1950s-1980s and over the 20th century lead to monsoon reductions. Logically, monsoon would be enhanced in the opposite situation (i.e. reducing aerosols), which matches the first half sentence saying that removing aerosols result in monsoon enhancement. We will add this logic in text.
—Lines 218-220: Sorry we made a mistake here. We will rewrite the sentence to "Over tropical and subtropical regions, 40 the overall uniform warming induce by mPWP boundaries (Plio_Pristine - PI) result in general decrease in sea level pressure and have relatively small effects on surface wind (Fig. 9a,c,e). Though removal of anthropogenic aerosols also show warming in tropical and subtropical regions, it rises the sea level pressure and have much stronger effects on surface wind that shows seasonal variances (Fig. 9b,d,f)."
—Technical corrections: We will make corrections as required.
References
Fedorov, A. V., Brierley, C. M., Lawrence, K. T., Liu, Z., Dekens, P. S., and Ravelo, A. C.: Patterns and mechanisms of early Pliocene warmth, Nature, 496, 43–49, https://doi.org/10.1038/nature12003, 2013.
Feng, R., Otto-Bliesner, B. L., Xu, Y., Brady, E., Fletcher, T., and Ballantyne, A.: Contributions of aerosol-cloud in- teractions to mid-Piacenzian seasonally sea ice-free Arctic Ocean, Geophysical Research Letters, 46, 9920–9929, https://doi.org/https://doi.org/10.1029/2019GL083960, 2019.
Haywood, A. M., Hill, D. J., Dolan, A. M., Otto-Bliesner, B. L., Bragg, F., Chan, W.-L., Chandler, M. A., Contoux, C., Dowsett, H. J., Jost, A., Kamae, Y., Lohmann, G., Lunt, D. J., Abe-Ouchi, A., Pickering, S. J., Ramstein, G., Rosenbloom, N. A., Salzmann, U., Sohl, L., Stepanek, C., Ueda, H., Yan, Q., and Zhang, Z.: Large-scale features of Pliocene climate: results from the Pliocene Model Intercomparison Project, Climate of the Past, 9, 191–209, https://doi.org/10.5194/cp-9-191-2013, 2013.
Haywood, A. M., Tindall, J. C., Dowsett, H. J., Dolan, A. M., Foley, K. M., Hunter, S. J., Hill, D. J., Chan, W.-L., Abe-Ouchi, A., Stepanek, C., Lohmann, G., Chandan, D., Peltier, W. R., Tan, N., Contoux, C., Ramstein, G., Li, X., Zhang, Z., Guo, C., Nisancioglu, K. H., Zhang, Q., Li, Q., Kamae, Y., Chandler, M. A., Sohl, L. E., Otto-Bliesner, B. L., Feng, R., Brady, E. C., von der Heydt, A. S., Baatsen, M. L. J., and Lunt, D. J.: The Pliocene Model Intercomparison Project Phase 2: large-scale climate features and climate sensitivity, Climate of the Past, 16, 2095–2123, https://doi.org/10.5194/cp-16-2095-2020, 2020.
Lamarque, J. F., Bond, T. C., Eyring, V., Granier, C., Heil, A., Klimont, Z., Lee, D., Liousse, C., Mieville, A., Owen, B., Schultz, M. G., Shindell, D., Smith, S. J., Stehfest, E., Van Aardenne, J., Cooper, O. R., Kainuma, M., Mahowald, N., McConnell, J. R., Naik, V., Riahi, K., and Van Vuuren, D. P.: Historical (1850-2000) gridded anthropogenic and biomass burning emissions of reactive gases and aerosols: Methodology and application, Atmospheric Chemistry and Physics, 10, 7017–7039, https://doi.org/10.5194/acp-10-7017-2010, 2010.
Citation: https://doi.org/10.5194/egusphere-2023-2702-AC1
-
RC2: 'Comment on egusphere-2023-2702', Anonymous Referee #2, 03 Jan 2024
- AC3: 'Reply on RC2', Anni Zhao, 23 Jan 2024
-
RC3: 'Comment on egusphere-2023-2702', Anonymous Referee #3, 09 Jan 2024
The climate in the mid-Pliocene Warm Period (mPWP) is usually viewed as an analog for future climate, but simulated mPWP climate change is largely different from the climate change in the 20th century. Also, there are large discrepancies between the simulation and proxies in the mPWP climate. To address the discrepancies, Zhao et al. suggested a different aerosol scenario from the pre-industrial aerosol setting should be used for simulating the mPWP climate. By removing pollutants of the industrial period in the mPWP climate simulation, the authors get more warming in the Northern Hemisphere and stronger ITCZ. The manuscript is well-written and I suggest a minor revision. My comments are below.
1. How the results of this study can help resolve the underestimation of temperature increase in the climate models should be addressed. In the abstract and Introduction, the authors mentioned discrepancies between models and proxies in the mPWP. One important difference is that the models underestimate the high temperature in the mPWP, especially in the high latitudes. When simulating the mPWP climate, people often use pre-industrial aerosol forcing, and the results of this study tell us that using pre-industrial aerosol forcing leads to increased warming. Thus, if we use more aerosol forcing, as the authors suggest the mPWP may have more aerosols, the simulated mPWP climate should be even cooler, and the discrepancies between the simulation and proxies would be larger. This confuses me and I think it is important to let readers know how considering aerosols forcing scenario can help improve climate simulations in the mPWP.
2. The title “Aerosol uncertainties in tropical precipitation changes for the mid-Pliocene Warm Period” confuses me. What does “aerosol uncertainties in tropical precipitation” mean? Does it mean the uncertainties of aerosol bring uncertainties in tropical precipitation in climate models?
L28: Repeated “e.g.”s
L39: “emission induced”: What emission? GHGs or aerosols?
L118 and L121: (Feng et al., 2022) -> Feng et al. (2022)
Figure 1: What are the circles in Fig. 1b? Do the proxies in Fig. 1b represent precipitation minus evaporation? If so, why not compare them to the simulated P-E? Also, please increase the white space between Figure 1a and 1b.
L169-171: If “removing aerosols causing more warming than the mPWP boundary conditions”, then why do you say that “the changes in boundary conditions are more important than aerosols?” This seems to contradict each other.
L212: Figure 6 is about droplet concentration. This should be Figure 7.
L219: “general increase in sea level pressure”: But the left panel of Figure 9 shows an increase in sea level pressure.
L227-228: I cannot see the “overall aerosol effect is more important” from Figure 10b. The numbers of dots above and below the 1:1 line are nearly equal.
L270: due to mPWP had warmer and wetter climate -> due to warmer and wetter climate in the mPWP
Citation: https://doi.org/10.5194/egusphere-2023-2702-RC3 - AC2: 'Reply on RC3', Anni Zhao, 11 Jan 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-2702', Anonymous Referee #1, 19 Dec 2023
Zhao et al. apply idealised aerosol scenario experiments to examine the importance of aerosol forcing on mPWP tropical precipitation and the possibility of aerosol uncertainty explaining the mismatch between reconstructions and simulations. Based on these simulations, the authors suggested that i) removal of aerosol pollutants cause global warming and further warms the Northern Hemisphere due to asymmetrical emissions; ii) the Intertropical Convergence Zone (ITCZ) becomes narrower and stronger and shifts northward after removal of anthropogenic aerosols. The content of this manuscript is potentially interesting and there is certainly publishable material in it. However, the manuscript is far from being acceptable to an international journal in its current form, as it has many scientific uncertainties for the reader. Some interpretations are self-contradictory and needs to be untangled. My detailed comments are listed as below.
- Line 51, the authors stated that “mPWP simulations now use modern-day or pre-industrial aerosol concentration that may differ from the conditions during the mPWP. It implies that aerosol effects may be one of the possible explanations for the mismatch between reconstructions and simulations”. However, in the experimental design, the authors also used the modern-day and pre-industrial aerosol concentration, and explained the mismatch between reconstructions and simulations based on these simulations, sinks into logic antinomy.
- The authors explained the spatial pattern of temperature change using asymmetrical emissions. However, the atmosphere is a dynamic collection of gases that constantly move and change, so the aerosols in the atmosphere will distribute globally. How can the aerosols keep asymmetrical distribution? The authors should give more discussion.
- Lines 169-171, these two sentences are contradictory, please check if the description is incorrect. Based on fig. 1a and fig. 5a, I think the mPWP boundary conditions cause more warming than removing anthropogenic aerosols.
- Line 176, the author stated that the ITCZ becomes narrower. However, I think it is really hard to get this conclusion only based on the precipitation changes. The authors should provide more convincing evidence.
- Lines 180-183, the authors stated that “The pattern of the magnitudes of tropical precipitation anomaly matches the tropical temperature warming over oceans”. I am unable to obtain this result from Fig 5. For example, the authors stated that tropical precipitation increases greater over the tropical Pacific and Indian Ocean, however, the temperature changes are similar over the whole tropical oceans.
- Lines 193-197, the sentence “Land regional……cooling effect” is hard to be understood. The first half of the sentence expresses that the monsoon are enhanced, but the second half shows that monsoon are weakened. Please rewrite.
- Lines 218-220, the sentence is self-contradictory. The authors stated Plio_Pristine - Plio_Polluted have relatively small effects on surface wind in the first half of the sentence, then stated that removing anthropogenic aerosols have much stronger effects on surface wind.
Technical corrections
- Please indent the first line of each paragraph, which makes easier for readers to read.
- Replace “0 - 0.8 °C” with “at 0-8 °C”, otherwise, it's hard to distinguish with minus sign. Please check the whole paper and correct it.
- In the Model description, please add some sentences to introduce the relation between the CESM and CCSM4. Moreover, add the full name of CCSM.
- line 175, add reverse parentheses “A2)”.
- Please improve the Figures. For example, i) delete the grid in the figures; ii) In figure 1, the “surface temperature change (℃)” coincided with “(b) PR Plio_Pristine – PI”.
Citation: https://doi.org/10.5194/egusphere-2023-2702-RC1 -
AC1: 'Reply on RC1', Anni Zhao, 09 Jan 2024
We would like to thank you for reviewing our manuscript and providing comments about our work. We are happy to adopt many of the comments and will revise the manuscript as requested.
—Line 51: A brief explanation is that the highlighted sentences say that simulated mPWP climate change does not include aerosol forcing, while our analysis mainly focuses on aerosol effects in mPWP simulations. The first highlighted sentence is trying to say that traditional mPWP simulations usually set prescribed aerosol concentrations same as the control runs, which means that they do not consider aerosol forcings. Our work uses three simulations: a pre-industrial control simulation (PI), a simulation with mPWP boundary condition plus pre-industrial aerosol (Plio_Pristine) and one with mPWP boundary condition plus industrial pollutants (Plio_Polluted). The simulated mPWP change from the highlighted sentence is equivalent to "Plio_Pristine - PI" in our study (Sect. 3.1). We then compares the simulated mPWP change (Plio_Pristine - PI) with the reconstructions in this section, in purpose of firstly evaluating our simulated mPWP climate and secondly pointing out the existence of data-model mismatch. Plio_Pristine - Plio_Polluted considers effects of aerosol forcing in the mPWP simulations (Sect. 3.2 and 3.3). Idealised aerosol scenarios were chosen, because the realistic mPWP aerosol concentrations are not available. Plio_Polluted uses industrial pollutants (Lamarque et al., 2010), which is a real existed aerosol forcing though not happened during the mPWP. Analysis related to aerosol effects does not touch data-model comparison. We will rewrite line 51 to "The discrepancy between mPWP simulations and reconstructions (Haywood et al., 2013, 2020) implies that models might miss some important mechanisms (Fedorov et al., 2013) or prescribed forcing could be a source of uncertainty (Feng et al., 2019). The mPWP simulations now use modern-day or pre-industrial aerosol concentration same as the control runs that may differ from the conditions during mPWP. Lack of including the effect of aerosol forcings and the usage of unrealistic prescribed aerosol concentration in mPWP simulations implies that aerosol effects may be one of the possible explanation for the mismatch between reconstructions and simulations."
—Aerosol distribution: Plio_Pristine and Plio_Polluted simulations in our study use prescribed aerosols, which give aerosol distribution instantaneously at the beginning and then left the model to respond to it. Aerosols do not distribute globally as the lifetime of aerosols is only a few weeks. The atmosphere is not well-mixed and the North-South difference emissions persists into concentrations.
—Lines 169-171: The mPWP boundary conditions cause more warming than removing anthropogenic aerosols. That’s what conclude in line 171 as "...This suggests that changes in boundary conditions are relative more important than aerosol effects in mPWP warming." We are trying to say that removing aerosols only causes more over Northeastern Pacific and high-latitude North Atlantic Ocean than the mPWP boundaries. We will rewrite the sentence to "However, the mPWP boundary conditions causes more warming than removing anthropogenic aerosols nearly global except Northeastern Pacific and high-latitude North Atlantic Ocean (Fig. 5a,c,e). More warming lead by the mPWP boundaries than removal of aerosols suggests ..." to emphasise that the mPWP boundaries lead to more warming than removal of aerosols.
—Line 176: We will add a figure and discussion about changes in the Hadley circulation.
—Lines 180-183: The temperature along the Equator in the Pacific Ocean is greater than surroundings. The warming band is largely overlap with the precipitation increase belt.
—Lines 193-197: The evidence (the citations in sentences) in the second half says that the cooling effect induced by in- creased aerosol during 1950s-1980s and over the 20th century lead to monsoon reductions. Logically, monsoon would be enhanced in the opposite situation (i.e. reducing aerosols), which matches the first half sentence saying that removing aerosols result in monsoon enhancement. We will add this logic in text.
—Lines 218-220: Sorry we made a mistake here. We will rewrite the sentence to "Over tropical and subtropical regions, 40 the overall uniform warming induce by mPWP boundaries (Plio_Pristine - PI) result in general decrease in sea level pressure and have relatively small effects on surface wind (Fig. 9a,c,e). Though removal of anthropogenic aerosols also show warming in tropical and subtropical regions, it rises the sea level pressure and have much stronger effects on surface wind that shows seasonal variances (Fig. 9b,d,f)."
—Technical corrections: We will make corrections as required.
References
Fedorov, A. V., Brierley, C. M., Lawrence, K. T., Liu, Z., Dekens, P. S., and Ravelo, A. C.: Patterns and mechanisms of early Pliocene warmth, Nature, 496, 43–49, https://doi.org/10.1038/nature12003, 2013.
Feng, R., Otto-Bliesner, B. L., Xu, Y., Brady, E., Fletcher, T., and Ballantyne, A.: Contributions of aerosol-cloud in- teractions to mid-Piacenzian seasonally sea ice-free Arctic Ocean, Geophysical Research Letters, 46, 9920–9929, https://doi.org/https://doi.org/10.1029/2019GL083960, 2019.
Haywood, A. M., Hill, D. J., Dolan, A. M., Otto-Bliesner, B. L., Bragg, F., Chan, W.-L., Chandler, M. A., Contoux, C., Dowsett, H. J., Jost, A., Kamae, Y., Lohmann, G., Lunt, D. J., Abe-Ouchi, A., Pickering, S. J., Ramstein, G., Rosenbloom, N. A., Salzmann, U., Sohl, L., Stepanek, C., Ueda, H., Yan, Q., and Zhang, Z.: Large-scale features of Pliocene climate: results from the Pliocene Model Intercomparison Project, Climate of the Past, 9, 191–209, https://doi.org/10.5194/cp-9-191-2013, 2013.
Haywood, A. M., Tindall, J. C., Dowsett, H. J., Dolan, A. M., Foley, K. M., Hunter, S. J., Hill, D. J., Chan, W.-L., Abe-Ouchi, A., Stepanek, C., Lohmann, G., Chandan, D., Peltier, W. R., Tan, N., Contoux, C., Ramstein, G., Li, X., Zhang, Z., Guo, C., Nisancioglu, K. H., Zhang, Q., Li, Q., Kamae, Y., Chandler, M. A., Sohl, L. E., Otto-Bliesner, B. L., Feng, R., Brady, E. C., von der Heydt, A. S., Baatsen, M. L. J., and Lunt, D. J.: The Pliocene Model Intercomparison Project Phase 2: large-scale climate features and climate sensitivity, Climate of the Past, 16, 2095–2123, https://doi.org/10.5194/cp-16-2095-2020, 2020.
Lamarque, J. F., Bond, T. C., Eyring, V., Granier, C., Heil, A., Klimont, Z., Lee, D., Liousse, C., Mieville, A., Owen, B., Schultz, M. G., Shindell, D., Smith, S. J., Stehfest, E., Van Aardenne, J., Cooper, O. R., Kainuma, M., Mahowald, N., McConnell, J. R., Naik, V., Riahi, K., and Van Vuuren, D. P.: Historical (1850-2000) gridded anthropogenic and biomass burning emissions of reactive gases and aerosols: Methodology and application, Atmospheric Chemistry and Physics, 10, 7017–7039, https://doi.org/10.5194/acp-10-7017-2010, 2010.
Citation: https://doi.org/10.5194/egusphere-2023-2702-AC1
-
RC2: 'Comment on egusphere-2023-2702', Anonymous Referee #2, 03 Jan 2024
- AC3: 'Reply on RC2', Anni Zhao, 23 Jan 2024
-
RC3: 'Comment on egusphere-2023-2702', Anonymous Referee #3, 09 Jan 2024
The climate in the mid-Pliocene Warm Period (mPWP) is usually viewed as an analog for future climate, but simulated mPWP climate change is largely different from the climate change in the 20th century. Also, there are large discrepancies between the simulation and proxies in the mPWP climate. To address the discrepancies, Zhao et al. suggested a different aerosol scenario from the pre-industrial aerosol setting should be used for simulating the mPWP climate. By removing pollutants of the industrial period in the mPWP climate simulation, the authors get more warming in the Northern Hemisphere and stronger ITCZ. The manuscript is well-written and I suggest a minor revision. My comments are below.
1. How the results of this study can help resolve the underestimation of temperature increase in the climate models should be addressed. In the abstract and Introduction, the authors mentioned discrepancies between models and proxies in the mPWP. One important difference is that the models underestimate the high temperature in the mPWP, especially in the high latitudes. When simulating the mPWP climate, people often use pre-industrial aerosol forcing, and the results of this study tell us that using pre-industrial aerosol forcing leads to increased warming. Thus, if we use more aerosol forcing, as the authors suggest the mPWP may have more aerosols, the simulated mPWP climate should be even cooler, and the discrepancies between the simulation and proxies would be larger. This confuses me and I think it is important to let readers know how considering aerosols forcing scenario can help improve climate simulations in the mPWP.
2. The title “Aerosol uncertainties in tropical precipitation changes for the mid-Pliocene Warm Period” confuses me. What does “aerosol uncertainties in tropical precipitation” mean? Does it mean the uncertainties of aerosol bring uncertainties in tropical precipitation in climate models?
L28: Repeated “e.g.”s
L39: “emission induced”: What emission? GHGs or aerosols?
L118 and L121: (Feng et al., 2022) -> Feng et al. (2022)
Figure 1: What are the circles in Fig. 1b? Do the proxies in Fig. 1b represent precipitation minus evaporation? If so, why not compare them to the simulated P-E? Also, please increase the white space between Figure 1a and 1b.
L169-171: If “removing aerosols causing more warming than the mPWP boundary conditions”, then why do you say that “the changes in boundary conditions are more important than aerosols?” This seems to contradict each other.
L212: Figure 6 is about droplet concentration. This should be Figure 7.
L219: “general increase in sea level pressure”: But the left panel of Figure 9 shows an increase in sea level pressure.
L227-228: I cannot see the “overall aerosol effect is more important” from Figure 10b. The numbers of dots above and below the 1:1 line are nearly equal.
L270: due to mPWP had warmer and wetter climate -> due to warmer and wetter climate in the mPWP
Citation: https://doi.org/10.5194/egusphere-2023-2702-RC3 - AC2: 'Reply on RC3', Anni Zhao, 11 Jan 2024
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Ran Feng
Chris M. Brierley
Jian Zhang
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