the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Aug 2026
Characterizing Natural Aerosol Variability and its Uncertainty in the Earth System
Abstract. Aerosol radiative forcing represents the largest source of uncertainty for calculating present-day climate sensitivity. This uncertainty has been underestimated in climate models, as they have not adequately accounted for uncertainties in the emissions of aerosols prior to the satellite era. This is especially the case for natural aerosols, such as mineral dust and aerosols from biomass burning. In this paper, we take a step towards reducing this uncertainty by providing a roadmap for improved integration of proxy-based observational constraints on past aerosol variability with model simulations. We first review existing literature on the importance of natural aerosol radiative forcing during historical and paleo-time periods, with a focus on the Last Glacial Maximum and the preindustrial era (ca. 1850) to the present. We then compile existing paleo-data archives and describe their ability to constrain emissions of aerosols, highlighting existing gaps. Model-data combinations are available to estimate radiative effects for dust and volcanoes in several time periods, and for biomass burning for preindustrial to present day, but are not available for other aerosols. Modeled feedbacks of aerosols to climate (W/m2/°C) are 10–100⨉ lower than model-data derived estimates for dust, casting doubt on our ability to successfully model feedbacks in the current generation of Earth system models. Finally, we propose a framework for integrating paleo-archives with models through harmonized datasets, proxy–model translation metrics, and regularized inversion approaches, and identify priority measurements needed to reduce uncertainty in both aerosol loading and radiative-effect efficiency across climate states.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-4532', Anonymous Referee #1, 07 Oct 2026
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RC2: 'Comment on egusphere-2026-4532', Anonymous Referee #2, 20 Oct 2026
The manuscript is a review of the available data on natural aerosol variability, aerosol effective radiative forcing, and the uncertainties of both in the pre-industrial and paleo-time periods. It gives a thorough overview of the available proxies for mineral dust, biomass burning, volcanic emissions, and marine and other aerosols. It also provides a suggested ‘roadmap’ for dataset synergy going forward. It represents a substantial contribution to the field of atmospheric science and paleoclimate. My recommendation is for publication following minor revisions.
General comments
- More specific advice about combining uncertainties in section 7.3 would be very welcome. This is an essential section and currently feels short. Also, the abstract mentions ‘regularised inversion approaches’, but there isn’t a lot of advice on how to regularise them.
- The claim that modelled dust feedbacks are up to 100x lower than are consistent with the record is not the ‘headline’ result that the placement in the abstract suggests it is. The derivation from a range for instantaneous forcing divided by a range for the temperature change is not strong enough to hold up the claim that this ‘casts doubt on our ability to successfully model feedbacks in the current generation of Earth system models’. It’s also slightly off-angle from the main contribution of the paper as a review and roadmap. Also, the ranges for PI–PD dust changes quoted in the introduction are not the same as those section 3.1.1.
- It would be very helpful to see even a minimal worked example for the ladder for a specific aerosol type using real datasets. This reader also still came away uncertain as to how the obstacle of geographically limited proxies can be overcome to form global datasets.
- Tables 4 and 5 mix instantaneous radiative effect, RF and ERF in the same columns. They both also seem incomplete. These two tables are central to the paper and need to be standardised for consistency and reviewed to ensure completeness.
Lines 191–192: ‘Aerosols are included in most ESMs so that their interactions with [...] varying sources and sinks [...] can be included’ – awkward phrasing to say that aerosols interact with their sources and sinks: rephrase.
Lines 317–321: This seems like two separate sentences, one ending at ‘escarpments’ and one beginning at ‘Post-depositional’.
Line 354: ‘Post-industrial’ sounds like a future scenario – rephrase as ‘present-day’.
Lines 452–453: ‘yet many of these properties remain simplified or poorly constrained in paleoclimate simulations’ – this could be expanded on, especially given the constructive focus of this paper on the use of proxies to improve modelling.
Lines 523–524: ‘Together with changes in surface albedo’ – the mention of surface albedo came unexpectedly. What proxies are there for albedo? This sentence seems to have been constructed with knowledge not available to the reader, at least this reader.
Lines 705–706: ‘The predominantly organic matrix also contains only trace amounts of mineral material, sometimes below the detection limits for mineralogical characterization’ – again, confusing to someone in the aerosol modelling field not expert in proxies. Trace amounts of pre-existing mineral material sounds like the peat would be a good matrix for trapping mineral dust, not a disadvantageous one as the framing seems to suggest.
Line 890: 1997 is not the usual threshold for the beginning of the satellite era – either say 1970s or specify why this specific year is chosen.
Lines 901–917: reformat with a new line for each numbered heading, as this is a very long sentence on its own.
Lines 1004–1005: ‘mixed contributions from both biomass burning and fossil fuel sources [...] particularly during the industrial era’ – do fossil fuel sources contribute prior to the industrial era? I would assume that this was limited to the industrial era. If not, briefly explain.
Line 1233: ‘The impact of fire on dust likely changes the further back in time is explored’ – awkward, rephrase.
Line 1665: ‘emitted directly by humans’ → ‘emitted directly by human activity’; similarly line 1747 ‘while humans can directly emit’ → ‘while human activity can directly emit’
Lines 1779–1781: ‘One important issue is that paleoaerosol modelers calculate the effective radiative forcing, not just the instantaneous radiative forcing’ – please explain with an additional sentence or two why this is important.
Technical comments:
There are a number of instances of unnecessarily italicised text (e.g. lines 202–206). There are also a few instances of extra spaces. There are also some instances of unnecessary bolding (e.g. line 1302) and one instance of unnecessary capitalisation (line 1353).
A few inconsistencies naturally arise from having multiple authors. ‘Aeolian’ vs ‘eolian’ is one, also ‘paleo aerosol’, ‘paleo-aerosol’, ‘paleoaerosol’.
Line 271: ‘complicated for the highly spatially’ → ‘complicated by the highly spatially’
Line 367: Delete ‘Therefore’ at the beginning of the sentence – it doesn’t follow as a logical conclusion from the previous sentence.
Lines 365–366: ‘Some corals provide highly indirect dust records because they reflect water column geochemistry rather while others record direct atmospheric deposition Eakin’ – delete one of ‘rather’ or ‘while’ and add parenthesis → ‘atmospheric deposition (Eakin’
Line 1176: ‘ice core black carbon, tree ring fire scars’ → ‘ice core black carbon, and tree ring fire scars’
Line 1459: ‘temporally’ → ‘temporary’
Line 2135: ‘ARE; ’ → ‘ARE: ’
Figures and tables:
Table 1: ‘Fire scars’ should be capitalised for consistency.
Table 2: While DMAR is defined in the glossary, it would be helpful to define it in-text also.
Table 4: It should be noted what blank cells in this table mean, if they cannot be filled in (?). For example, the ‘Open Fires’ total ERF is not equal to just the ERFari, though the ERFaci is blank.
Citation: https://doi.org/10.5194/egusphere-2026-4532-RC2
Data sets
Vegetation cover and wildfire in the late Preindustrial, mid-Holocene, and Last Glacial Maximum Authors/Creators Jed Kaplan https://zenodo.org/records/20821425
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- 1
This manuscript is a broad community review of natural aerosol variability and its uncertainty in the Earth system. It synthesizes Earth system model estimates and paleoclimate proxy archives for dust, biomass-burning, volcanic, and marine aerosols across the Last Glacial Maximum and the preindustrial-to-present transition. The paper is timely, comprehensive, and well referenced. It will be a valuable resource for both the paleoclimate and aerosol-modeling communities. I recommend publication after the authors address the points below.
General Comments:
Minor Comments:
Lines 193–194: The text first describes aerosols forming in the atmosphere (SO2 to sulfate). Please introduce the term “secondary aerosols” here, as the distinction is used later.
Line 270: “millenial-scale” should be “millennial-scale”.
Line 1684: “Rap et al,. 2013” should be “Rap et al., 2013”.
Line 1739: “Moschos et al.,. 2022” should be “Moschos et al., 2022”.
Line 1741: “Tsigaridis and and Kanakidou, 2018” has a duplicated “and”.
Line 1811: “…for calculating radiative forcing,. The ladder…” has a stray “,.”. Use a single period.
Line 2060: “…is available.. Careful…” has a double period. Use one.
Table 6 caption: It refers to “(Table 6: −2 to 0.1 W/m2)” inside Table 6. This value comes from Table 5, so the cross-reference should read “Table 5.”
Section references: Line 1769 says “Sections 3–6,” but the Table 4 caption and line 1633 say “Sections 2–6.” The aerosol sections are 3–6. Please make these consistent.