Overview – this study investigates historical (1920-2000) and future (2000-2080) changes in near surface pressure and winds over the South Pacific using a combination of a spatially complete paleoclimate reconstruction and a large suite of climate model simulations.  It provides convincing evidence of the relative roles of internal variability and forced variability (from greenhouse gases and ozone depletion).  Importantly, the paper also provides a much-needed possible narrative for the roles of natural variability followed by external forcing to understand historical variations in ice loss from the WAIS since 1940s.

The paper is very well written, easy to follow, and the scientific analysis in my perspective is sound.  The team is to be commended on this excellent study, which is well conceived and an important scientific advancement. The authors note many caveats to the present study, which I also appreciate. 

My main concern is that the paper is primarily based on gridded model or paleoclimate-based reconstruction data, and does not incorporate the wealth of observations other than ERA5 after 1979. It would be helpful to see the agreement between the reconstruction at least and pressure observations (available across all SH midlatitudes since 1920, and Orcadas since 1903) to see at least the agreement in South America / South Atlantic.  For more complete investigation on the agreement (and for some aspects of the deepening of the ASL), comparisons could be made with Antarctic data after 1957 when trends seem quite large (making note to include the critical point of Byrd station in West Antarctica as another potential estimate of observed change near the Amundsen Sea apart from measurements along the Antarctic Peninsula).  I do feel the point observations comparisons with the reconstructions would help to understand changes in observations apart from paleoclimate data and climate model data, and would round out the paper well (1 more figure), and provide further validation for the reconstruction that is not provided in the preceeding O’Connor et al. paper. 

Minor comments:

Abstract – would be ideal to clarify the ice loss was not in reference to sea ice, but the grounded ice sheet

L255-260, Fig. 1f – I also suspect the response to ozone is weaker as it is seasonally varying (strongest in DJF at the surface), so the annual mean reduces this signal.

Wondering what role incorrect sea ice trends in the model may play in both the historical and future simulations?  The climate model tends to overestimate observed sea ice trends compared to observations.  Importantly, the sea ice trends have been most pronounced in the Pacific sector in observations, which is the area of study, so it is possible that there could be some impact of this on the pressure and wind trends in the region from the model, especially in the model ensemble means.  Can the authors comment on this potential error, where appropriate, in the paper?

L595-603 – really appreciate mentioning the caveats to the study.  I think it is also important to mention that the study masks seasonal variability, limited by the paleoclimate reconstruction, that is important for tropical teleconnections (i.e., internal variability) and the role of ozone forcing. 

This study investigates potential drivers of trends in near-surface pressure and winds over the Amundsen Sea, with a view to understanding the decline of the West Antarctic Ice Sheet over the past century. It uses a paleoclimate reconstruction of global fields alongside a series of large ensemble simulations with different forcings. The study concludes that internal climate variability has played a dominant role, particularly in the ice shelf and break region, with forced variability (greenhouse gases and ozone depletion) significantly contributing in the later 20^th century and future.

This paper addresses an important issue in understanding and attributing the drivers of West Antarctic climate change. I enjoyed reading the study and found the text and figures to be clear and logically-structured. I think that this study is very suitable for publication in The Cryosphere and have just a few minor comments, which I hope the authors will find useful.

Minor comments:

1. In my view, the main caveat with this study is the reliability of the paleoclimate reconstruction used. In the short period of overlap between the satellite era (using ERA5) and the reconstruction, correlations of zonal winds are relatively modest at 0.35-0.6 (Fig 4). The paper does a good job of acknowledging and discussing this caveat, however I think that it would benefit from a little more detail on the reliability of the reconstruction. I would suggest that the authors include a comparison with the full ERA5 record (1950-present) in Fig 4. Although the reanalysis will also be substantially less reliable before the satellite era, there are in situ observations that will lend some skill during this time period, such that I believe the comparison is worthwhile.

2. L411, Fig 6: The text discusses the correlations as statistically significant, indicating a strong relationship between the IPO and internal variability in zonal wind in the three regions. However, although the (annual) correlations are significant, I think it should also be mentioned that they are relatively small, meaning that the IPO can only explain at most ~25% of the variance in internal variability.

3. L580: It is discussed here that future wind trends on the shelf are determined only by internal variability (not emissions scenario). It is also stated (e.g. L638) that mitigation of wind-driven ice loss will require strong emissions mitigation. This may perhaps be confusing, and so I would suggest some discussion here of whether winds over the deep ocean, shelf break, or shelf are expected to play the larger role in driving ice loss. If the shelf winds are thought to dominate, then these results might suggest emissions mitigation will have little impact on wind-driven ice loss.