Atmos. Chem. Phys., 14, 2987-3015, 2014
www.atmos-chem-phys.net/14/2987/2014/
doi:10.5194/acp-14-2987-2014
© Author(s) 2014. This work is distributed
under the Creative Commons Attribution 3.0 License.
Further evidence of important environmental information content in red-to-green ratios as depicted in paintings by great masters
C. S. Zerefos1,2, P. Tetsis1, A. Kazantzidis3, V. Amiridis4, S. C. Zerefos5, J. Luterbacher6, K. Eleftheratos7, E. Gerasopoulos2,8, S. Kazadzis8, and A. Papayannis9
1Academy of Athens, Athens, Greece
2Navarino Environmental Observatory (N.E.O.), Messinia, Greece
3Laboratory of Atmospheric Physics, Physics Department, University of Patras, Greece
4Institute of Astronomy, Astrophysics, Space Application and Remote Sensing, National Observatory of Athens, Greece
5Hellenic Open University, Patras, Greece
6Department of Geography, Climatology, Climate Dynamics and Climate Change, Justus Liebig University of Giessen, Giessen, Germany
7Faculty of Geology and Geoenvironment, University of Athens, Greece
8Institute of Environmental Research and Sustainable Development, National Observatory of Athens, Greece
9National Technical University of Athens, Athens, Greece

Abstract. We examine sunsets painted by famous artists as proxy information for the aerosol optical depth after major volcanic eruptions. Images derived from precision colour protocols applied to the paintings were compared to online images, and found that the latter, previously analysed, provide accurate information. Aerosol optical depths (AODs) at 550 nm, corresponding to Northern Hemisphere middle latitudes, calculated by introducing red-to-green (R / G) ratios from a large number of paintings to a radiative transfer model, were significantly correlated with independent proxies from stratospheric AOD and optical extinction data, the dust veil index, and ice core volcanic indices. AODs calculated from paintings were grouped into 50-year intervals from 1500 to 2000. The year of each eruption and the 3 following years were defined as "volcanic". The remaining "non-volcanic" years were used to provide additional evidence of a multidecadal increase in the atmospheric optical depths during the industrial "revolution". The increase of AOD at 550 nm calculated from the paintings grows from 0.15 in the middle 19th century to about 0.20 by the end of the 20th century. To corroborate our findings, an experiment was designed in which a master painter/colourist painted successive sunsets during and after the passage of Saharan aerosols over the island of Hydra in Greece. Independent solar radiometric measurements confirmed that the master colourist's R / G ratios which were used to model his AODs, matched the AOD values measured in situ by co-located sun photometers during the declining phase of the Saharan aerosol. An independent experiment was performed to understand the difference between R / G ratios calculated from a typical volcanic aerosol and those measured from the mineral aerosol during the Hydra experiment. It was found that the differences in terms of R / G ratios were small, ranging between −2.6% and +1.6%. Also, when analysing different parts of cloudless skies of paintings following major volcanic eruptions, any structural differences seen in the paintings had not altered the results discussed above. However, a detailed study on all possible sources of uncertainties involved (such as the impact of clouds on R / G ratios) still needs to be studied. Because of the large number of paintings studied, we tentatively propose the conclusion that regardless of the school, red-to-green ratios from great masters can provide independent proxy AODs that correlate with widely accepted proxies and with independent measurements.

Citation: Zerefos, C. S., Tetsis, P., Kazantzidis, A., Amiridis, V., Zerefos, S. C., Luterbacher, J., Eleftheratos, K., Gerasopoulos, E., Kazadzis, S., and Papayannis, A.: Further evidence of important environmental information content in red-to-green ratios as depicted in paintings by great masters, Atmos. Chem. Phys., 14, 2987-3015, doi:10.5194/acp-14-2987-2014, 2014.
 
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