Radiative Energy Flux Variation from 2001–2020

Round 1

Reviewer 1 Report

I thank the authors for taking my initial review into consideration. Now I only have several minor comments:

• Line 25: “Since” should be “For”
• Line 52: “modelling” should be “modeling”
• Line 250-251, “CO2 has increased … from 2001 to 2020.”: please add references
• Line 277: “und” should be “and”
• Table 2a: “SW Flux Down-Clear Sky-Surface Global”, “Rel. Error”, please double check the value of “14723”

Author Response

Please see attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Review of Dübal and Vahrenholt: “Radiative Energy Flux Variation from 2001–2020”

General Comments:

This manuscript by of Dübal and Vahrenholt presented results about long-tern changes of the radiative fluxes at the top-of-atmosphere (TOA) and surface from 2000 to 2020 using observational records; CERES datasets and others. Trend analysis (i.e. linear regressed analysis) for each component of the radiation budget and ocean heat content showed three key results. (1) Net radiative flux at TOA, which is equivalent to Earth Energy Imbalances (EEI), increased in recent two decades due to the decrease of  the outgoing SW flux. (2) The changes in SW flux at TOA was mainly caused in “Cloudy Area” implying that changes in cloud structure is essential. (3) There is good agreement between the long-term changes in enthalpy calculated form ocean heat content (OHC) and observed net TOA flux in the present. (4) There are differences between these trends in the Northern and Southern Hemisphere, suggesting that large variability in the Northern Hemisphere but small one in the Southern Hemisphere. Overall, this study showed the current status of the radiation budget described by the satellite observation and gave some implications for long-term changes in EEI associated with the global warming.   

Although their results about long-term changes in TOA net flux and its relation with enthalpy changes are nicely shown, I found the paper very hard to follow. In particular, I repeatedly asked myself why these analysis were conducted while I was reading in section “4 Surface Fluxes”. If the authors want to emphasize the results of radiation budget at the surface, summary of the result should be included in the abstract. I think each section is organized well and gave us a lot of useful information from the results and figures, but the order of contents in the manuscript should be reorganized. I also recommend that the manuscript should be English-proofed so that the reader can smoothly understand its contents (I doubt that I can comment about English because I am not native English speaker. However, it is too hard to follow the manuscript).

Overall, I recommend the manuscript to “Major revisions”.

Other comments:

1. Section 3 (L166-168): The authors concluded that “cloud optical thinning” effect is most likely mechanism regulating the recent changes in SW and LW fluxes at TOA. Detail of the mechanism should be explained more with the references about the cloud changes associated with the global warming.
2. Caption of figures : Caption should be the explanation of the figure and not include the explanation of the results from the figure (e.g. caption of Fig.1; “The Southern hemisphere obtains ca. 0.7 W/m2 more than the North due to the eccentric orbit and the inclined axis of the earth.”).

Author Response

Please see attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Please, see the attached document.

Comments for author File: Comments.pdf

Author Response

Please see attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Congratulations to the authors that have improved the manuscript. They took into account all of my concerns. Therefore, I accept the manuscript in its present form.

Author Response

Thank you very much.

All the best,

Authors

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Synopsis

This paper utilized the CERES radiative energy flux data to analyze the variation and trend of the energy flux from 2001 to 2020. The authors suggested that there is a ~0.8 W/m^2 increase of the TOA net flux, and the major contributor to it is the decreased outgoing SW flux, which is related to clouds instead of the greenhouse gas effect. This paper also compares the SH and NH in terms of the TOA and surface LW and SW fluxes.

General Comments:

1. The method used to derive the linear trend in this study is missing. Because there are only 20 years of data, it’s critical to quantify the uncertainty and confidence level when using annual data to derive the linear trend.
2. The statement that the root cause of decreased SW flux is due to clouds instead of greenhouse gases seems weak to me. There is only one sentence of “If greenhouse gas emission were the root cause, it would expect a continuous warming” in lines 285-286. Since this is a main point that the authors try to make, I would suggest adding references or justifications to support this point.
3. Descriptions of the data used to generate figs. 7 and 9 are missing.
4. I wonder whether it should be decimal point “.” instead of the comma “,” for the decimal numbers in the text?

Detail Comments

1. Line 43, “respectively”: does the author mean “correspondingly”?
2. Session 2: what is the spatial resolution of the CERES data?
3. Line 57: one “from” is redundant in this sentence.
4. Line 80, “the quoted literature”: which literature the authors referred to?
5. 4 was not mentioned in the text.
6. Line 217: “It looks as if …” is not a scientific way to express a statement on paper.
7. Line 69, 220, 246, 255: missing “,” in front of “etc.”
8. Line 98: “to” is redundant in front of “cause”
9. Line 110: “difference” should be “differences”
10. Line 133: missing “,” in front of “which”
11. Line 135: redundant “,” after assumed
12. Line 147: redumdant “a” after “W/m2”
13. Line 178: “are” should be “is”
14. Line 197: “has” should be “have”
15. Line 251, 305: “since” should be “for”
16. Line 260: “large” should be “larger”
17. Line 297: “were” should be “was”

Reviewer 2 Report

The authors demonstrate variations in the NASA CERES dataset and report trends in fluxes from 2001 to 2020. Unfortunately, this subject has been extensively investigated by several authors, especially the team that generates the dataset during the validation process. I suggest the authors carefully consider what has been investigated in the past and present new findings (if any). Some papers to reflect are:

1. Loeb, N. G., Johnson, G. C., Thorsen, T. J., Lyman, J. M., Rose, F. G., & Kato, S. (2021). Satellite and ocean data reveal marked increase in Earth’s heating rate. Geophysical Research Letters, 48
2. Kato, S., Rose, F. G., Rutan, D. A., Thorsen, T. J., Loeb, N. G., Doelling, D. R., Huang, X., Smith, W. L., Su, W., & Ham, S. (2018). Surface Irradiances of Edition 4.0 Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) Data Product, Journal of Climate, 31(11), 4501-4527.
3. Loeb, N. G., Doelling, D. R., Wang, H., Su, W., Nguyen, C., Corbett, J. G., Liang, L., Mitrescu, C., Rose, F. G., & Kato, S. (2018). Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) Top-of-Atmosphere (TOA) Edition-4.0 Data Product, Journal of Climate, 31(2), 895-918.
4. Loeb, N.G.; Thorsen, T.J.; Norris, J.R.; Wang, H.; Su, W. Changes in Earth’s Energy Budget during and after the “Pause” in Global Warming: An Observational Perspective. Climate 2018, 6, 62.

Other points:

1. No error analysis has been conducted, especially with trend estimation. This should be clearly outlined in the methods section.
2. NASA CERES dataset is on Terra and Aqua. The authors should be careful in using cloud dataset which sub-samples the same clouds seen by CERES footprint. For example, CERES Energy Balanced and Filled (EBAF) Ed4.1 product already has cloud relevant information.
3. The figures are of poor quality/resolution.