This manuscript presents a method for propagating local sea-ice concentration uncertainties to hemispheric sea-ice area estimates over the passive microwave record. The study makes three clear contributions that advance our understanding of observational uncertainty in sea ice. 

1. The work provides a dynamic, daily and monthly uncertainty product that is self-contained within a single satellite record (OSI SAF) and does not depend on the availability or selection of other products. This fills a gap in the community's toolkit for assessing the significance of new SIA extremes and for climate model evaluation. 

2. Secondly, the authors identify the Marginal Ice Zone as the primary physical driver of the seasonality of SIA uncertainty.  

3. Finally, the comparison between the single-product stochastic uncertainty and the inter-product spread provides compelling evidence that the large differences between existing SIA trend estimates are dominated by systematic methodological choices in the processing chains, rather than noise.  The implication that extending the time series alone will not resolve trend uncertainties is an important message for both the observational and modelling communities. 

The study is both timely and important. Reliable uncertainty estimates for SIA are needed for climate assessments and model evaluation, but little is known about these uncertainties over the full satellite record. By separating the stochastic and systematic components, the authors provide appropriate uncertainty estimates for relative comparisons. The Monte Carlo generates a 50-member ensemble that preserves the spatial and temporal error correlations. Three refinements to a previously published method improve consistency with the operational sea ice index. The study acknowledges limitations: it relies entirely on the OSI SAF SIC uncertainties without independent verification and only partially captures systematic errors from melt ponds and interpolation. However, this first step constitutes an important contribution and, following consideration of my points outlined below, would make an interesting contribution to The Cryosphere

The manuscript is generally well-structured and explains complex statistical concepts clearly, though some sections rely heavily on prior work. The statistical framework is rigorous, the validation strategy of comparing the ensemble spread against bias-corrected inter-product differences is well conceived, and the paper is concise and logically structured. 

Major concerns:

1. Definition of the MIZ. The finding that SIA uncertainty scales with the square root of MIZ length (the 50% SIC contour) is important. But the width of the MIZ varies regionally and seasonally due to wave exposure, ocean heat and ice dynamics. This is particularly relevant for Antarctica, where a substantial MIZ is almost always present. Would a 2D metric (e.g. MIZ area, or area of grid cells within 15-80% concentration or similar) provide a stronger or more physically complete predictor? If MIZ length already captures most of the variability, demonstrating this explicitly would strengthen the physical interpretation and help assess robustness under future conditions where MIZ character may change. 

2. The paper relies heavily on Wernecke et al. (2024), and while the three refinements introduced here are clearly described, readers unfamiliar with the earlier work may struggle to follow key steps. I found it necessary to consult the 2024 paper to fully understand the processing chain. A brief step-by-step summary of the workflow (even in schematic or bullet-point form) would substantially improve accessibility without requiring full re-derivation of the method.  

3. The authors are transparent that their method is fully reliant on the SIC uncertainty component from OSI SAF without independent verification. The agreement with bias-free inter-product spread provides indirect validation, but a discussion on whether this could be partly coincidental if both approaches share common limitations would be helpful/ A brief sensitivity analysis, or at a minimum adding a short discussion of how results might change if input SIC uncertainties were scaled by some factor, would help readers assess the robustness of the quantitative estimates. 

Minor points

Title: The current title repeats "Sea-Ice Area" twice, which reads awkwardly. You might consider rewording this. 

Abstract: The finding about systematic uncertainties and their implications for trend analysis is arguably the paper's most consequential message, but is somewhat buried in the final sentences. You might consider elevating this. Several sentences are long and could be broken for clarity. Hedging phrases such as "so called" and "among other things" could be trimmed without loss of meaning. 

Figure 1 caption: the abbreviation STD is not defined (elsewhere in the manuscript your write out "standard deviation").

Line 120: (or at the most appropriate location) The choice of 60 Monte Carlo ensemble members is stated but not justified. A brief note on why 50 is sufficient or a reference to convergence testing in the 2024 paper would be helpful.

Line 151:  "ocen" should read "ocean"

This paper presents an improved uncertainty estimation method to propagate local OSI SAF sea-ice concentration uncertainties to hemispheric sea-ice area uncertainty estimates. The results show that the seasonal variability of SIA uncertainty is more closely related to the spatial distribution of sea ice than to the seasonal cycle of SIA itself. The authors further compare these stochastic uncertainty estimates with the inter-product spread from the UHH SIA product. After removing their systematic biases, the remaining differences between SIA products are consistent with the proposed single-product uncertainty. They also suggest that the difference between SIA trend estimates is largely driven by systematic methodological differences. The study represents a timely and valuable contribution, particularly given that uncertainty quantification for long-term SIA records remains insufficiently developed. The manuscript is generally well written, and the results are of clear interest to the community. Overall, I support publication after minor revisions.

General comments：

Using the local SIC uncertainty estimates from the OSI SAF product is reasonable. While these uncertainties are discussed later in Section 5.2, the manuscript lacks a general description of these uncertainties at their first introduction. It would be helpful to include a brief overview of the OSI SAF SIC uncertainty, particularly in Section 2.1 (Lines 68–73), as this would help readers better understand what sources of uncertainty are represented in the subsequent SIA uncertainty estimates.

It would be helpful to clarify the rationale for defining the size of the MIZ as the 50% SIC contour of the 25 km resolution SIC product (Line 153), and to briefly discuss the advantages of this choice. This definition may influence the results, particularly in fragmented coastal regions or areas with low ice concentration.

Figure 4: Why are the probability distributions of the SIA trend ensemble estimates in the Arctic similar in March and September, whereas in the Antarctic they differ markedly, with a smaller distribution in March and a larger one in September? Could this difference be related to the number of available SIA products included in the analysis (as mentioned in Sect. 5.3, where only a small number of products are used for March)? Please clarify and discuss this point.

Supplementary Figures 2 and 3: The black line marking the 50 % SIC contour is not very clear in several panels, as it appears to overlap visually with the land mask or coastline. I guess you could consider using a more contrasting color or line style to improve visibility.

Specific comments:

Line 12: “is characterized by” should be “are characterized by”.

Line 151: Typo, “ocen” should be “ocean”.

Line 233: the correlation of sea ice cover variability with climate indices?

Line 200: “effected by” should be “affected by”.

Line 240: “represent” should be “represents”.