The authors have addressed good portions of the original criticisms in their letter and in a revised manuscript sent to me personally.

However, there remain problems, especially in the writing. There are numerous items that need clarification so that most readers can follow smoothly. I have gone through the first half of their revised manuscript in detail and made comments. Ideally, they can recognize the issues, and clean the entire manuscript.

I will tentatively accept the manuscript, if the authors can make the work solid and at a level appropriate for CoP.

Jerry

Dear Xiao-Yan Liu,

This is a much-improved manuscript. I am happy to accept for the special issue of Climate of the Past, with a few revisions. The primary ones are two (A and B, below).

Sincerely,

Gerald (Jerry) Dickens

The Title is a bit awkward. I think it should read “Estimates of late middle Eocene pCO2 based on stomatal density of modern and fossil Nageia leaves”. This better incorporates the contents of the manuscript with correct grammar. Also, I think ~40 Ma is better described as late middle Eocene, and I do not think Gaertner needs inclusion as the genus, while not well known, is well established.

Lines 44-47: This is over-referenced and arguably incorrect. I would just put “In particular, there are few reconstructions for the late middle Eocene.” (And then cite those papers that show this aspect).

Line 128: I think this should be “… into two “sections”, …” (I assuming here that sections is a biological classification term).

Line 134: Needs space.

Lines 161-162: I think this should be “… surfaces of leaves might be used …”

Lines 173-174: This should be “… hours, the reaction was stopped when specimen fragments … and transparent. The …” (There should be no semicolons in this case).

Line 175: Should be “After, the ...”

Line 178: Needs period as already has an “and” (i.e., “… 30 min). The …”)

**A** Lines 192-197: This needs rewriting as important information is missing. It should be something like “Further information on the sections is provided by Lie et al. (2015). Importantly, the formations span a depositional age of approximately XX to YY Ma, or late middle Eocene (REF). This has been determined HOW? (1-2 sentences). Now start new paragraph “Macrofossil …” (Are other approaches the same as for modern leaves? This is not crystal clear right now).

Line 216: Remove space.

Line 229: Spell-out “Figure”

Line 245: Indent paragraph.

Line 293: Should be “For modern Nageia, we find that … increase, but that …”

Lines 295-296: Should be “… case has been observed for some flora.”

Line 300: Can remove “herein …”. Just end the sentence after “cells.”

Line 301: Start new paragraph and indent.

Lines 312-313: Tense. Should be “… was young or mature, or grew in a sunny or shady environment”.

Lines 321-322: Should be “…, which is fairly close to GEOCARB III predictions …”

Lines 326-327: Should be “… were generally lower than during much of the Cretaceous, but probably also decreased significantly from the early to late Eocene (REF). Here, I would fix the references. For example, two sets of references not needed, and Zachos et al. 2001 does not really discuss pCO2.

Lines 330-334: I would change to “However, there is a wide range of estimates for the Eocene (REF).” (Then remove the rest, as it is not really pertinent).

**B** Lines 336-380: This needs to be condensed and rewritten. All that should be here are past estimates for the middle to late Eocene, and how the Nageia estimates compare. However, there is a critical piece of information that needs to be tied in with the comment above. The world was dynamic in the Paleogene, including in the late middle Eocene, when the MECO occurred. Thus, the exact age matters, and it is possible that a values may differ because of slight offsets in time.

I believe that some readers may still find the scope of the manuscript too narrow. However, I also think the manuscript opens the door to further discussion on the use of leaf stomata. Further torquing of the last few paragraphs also could be made.

Nonetheless, I think the manuscript is now suitable for publication in CoP.

Jerry Dickens