Reply to I. Pérez (Reviewer #1)

We would like to thank I. Pérez for the constructive and helpful comments. The reviewer’s contribution is recognized in the acknowledgments of the revised manuscript. Below follows our response point by point. The reviewer’s comments are given in italic and our response is given in bold font.

1) The Reviewer notes: “The authors should think about procedures to increase the number of potential readers. Perhaps the authors should highlight the reasons for the selected region and they should underline if the procedure could be applied in different areas and they should compare the obtained results with those calculated for other regions.”

In our study we used AerChemMIP experiments, which incorporate global anthropogenic aerosol emission databases (Hoesly et al., 2018; van Marle et al., 2017). Therefore, our methodology could be applied to any region. The Mediterranean Basin is considered a climate hotspot due to the accelerating surface warming it has experienced during the last decades, especially during the summer. The Mediterranean’s sensitivity to global emission changes can have implications for heatwaves, droughts, and the water balance in a future climate state, affecting the lives of over 500 million people. With that in mind, we tried to fill some knowledge gaps in the literature by advancing attribution, mechanistic understanding, and quantification of the Mediterranean warming. Changes have been made to the Introduction to address the reviewer’s comment.

2) The Reviewer notes: “The authors consider the regions with impact on the Mediterranean basin. However, they should indicate the regions beyond Europe influenced by the studied area.”

Our study focuses on how global anthropogenic aerosol changes have impacted the Mediterranean Basin during the last decades. While European and North American aerosol emissions have significantly decreased since around the 1980s, the changes over the Mediterranean discussed in this paper are induced by aerosol emission changes all over the globe. It is not possible to address how changes over the Mediterranean alone can affect other parts of the world using the AerChemMIP experiments, since the anthropogenic aerosol emissions used in CMIP6 Earth system models are taken from global databases. Therefore, global changes cannot be attributed to changes in emissions over a single source region. There are other experiments one could use for such attribution studies, such as the those developed for the Precipitation Driver Response Model Intercomparison Project (PDRMIP) or the Regional Aerosol Model Intercomparison Project (RAMIP).

3) The Reviewer notes: “Monthly outputs were used. This period ignores short-term changes and the authors should value if these changes could be noticeable or not.”

The focus of this study is on radiative, temperature, and circulation responses on climatological and seasonal time scales, rather than on short-term (synoptic or intraseasonal) variability. Anthropogenic aerosol radiative forcing is usually calculated at monthly (or longer) time scale. This is because it reflects persistent changes in atmospheric composition and energy (radiative) balance caused by a climate forcer (in our case anthropogenic aerosols) rather than transient fluctuations driven by weather patterns.

Short-term variability at smaller time scales is expected to be dominated by internal atmospheric dynamics and does not significantly affect the multi-annual, ensemble-mean signals examined here. By averaging to monthly means reduces noise, allowing for robust identification of anthropogenic aerosol–induced changes across models. While short-term interactions between anthropogenic aerosols and meteorological processes may influence individual events, they are not expected to substantially alter the magnitude or sign of the long-term mean responses quantified in this work. Our paper focuses on annual and seasonal mean responses (from monthly mean data) over the Mediterranean Basin. Changes in extremes (e.g., daily maximum temperatures, maximum 1-day precipitation, etc.) are not considered here.

4) The Reviewer notes: “The authors consider two ten-year periods, 1970-1979 and 2005-2014 where a noticeable change of human activity is expected. However, they should indicate if both periods are similar from a meteorological point of view or not, since the atmosphere response depends on both, natural and human processes.”

The two decades considered in this study were selected to represent periods of contrasting anthropogenic aerosol forcing rather than distinct meteorological regimes. Initially two 20-year periods were used (i.e., 1965-1985 and 1995-2014) consistent with IPCC guidelines and qualitatively similar results were obtained. However, we focused on the periods of maximum (1970-1979) and modern (2005-2014) anthropogenic aerosol forcing to highlight the sensitivity of the Mediterranean to aerosol emission changes. In either case, internal meteorological variability is explicitly accounted for by using multi-model ensemble means and by averaging over ten-year periods, thus substantially reducing the influence of interannual variability associated with natural processes. Furthermore, the use of paired experiments with identical meteorological boundary conditions and forcings except for anthropogenic aerosol emissions (histSST minus histSST-piAer and historical minus hist-piAer) allows attribution of changes to anthropogenic aerosols. The experimental design of AerChemMIP isolates the anthropogenic aerosol contribution to the radiative budget, temperature and circulation irrespective of background meteorological differences between the two periods. As a result, the calculated differences primarily reflect the climate responses to changes in anthropogenic aerosol emissions rather than differences in the underlying meteorological state.

5) The Reviewer notes: “The main inconvenience is the lack of references in the results section to compare this analysis with previous studies. Perhaps some references could be transferred from other sections to discuss the results or some new references could be introduced.”

We agree that placing selected references directly in the Results section can help the reader better contextualize our findings relative to previous studies. Therefore, we have revised the Results section to include references where our results confirm, extend, or differ from earlier work.

References

Hoesly, R. M., Smith, S. J., Feng, L., Klimont, Z., Janssens-Maenhout, G., Pitkanen, T., Seibert, J. J., Vu, L., Andres, R. J., Bolt, R. M., Bond, T. C., Dawidowski, L., Kholod, N., Kurokawa, J., Li, M., Liu, L., Lu, Z., Moura, M. C. P., O’Rourke, P. R., and Zhang, Q.:

Historical (1750–2014) anthropogenic emissions of reactive gases and aerosols from the Community Emissions Data System (CEDS), Geoscientific Model Development, 11, 369–408, https://doi.org/10.5194/gmd-11-369-2018, 2018.

van Marle, M. J. E., Kloster, S., Magi, B. I., Marlon, J. R., Daniau, A.-L., Field, R. D., Arneth, A., Forrest, M., Hantson, S., Kehrwald, N. M., Knorr, W., Lasslop, G., Li, F., Mangeon, S., Yue, C., Kaiser, J. W., and van der Werf, G. R.: Historic global biomass burning emissions for CMIP6 (BB4CMIP) based on merging satellite observations with proxies and fire models (1750–2015), Geoscientific Model Development, 10, 3329–3357, https://doi.org/10.5194/gmd-10-3329-2017, 2017.

We would like to thank O. Haugvaldstad for the constructive and helpful comments. The reviewer’s contribution is recognized in the acknowledgments of the revised manuscript. In the attached file you will find our response point by point.