Reply to Comment by Strawa et al. (2025) on Webster and Warren (2022): “Regional Geoengineering Using Tiny Glass Bubbles Would Accelerate the Loss of Arctic Sea Ice”

[Geoengineering News]

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025EF006700?af=R

Authors: Stephen G. Warren, Melinda A. Webster

First published: 03 November 2025

https://doi.org/10.1029/2025EF006700

Abstract

Field et al. (2018, https://doi.org/10.1029/2018ef000820) had proposed spreading hollow glass microspheres (HGMs) over Arctic sea ice to increase its albedo. Webster and Warren (2022, https://doi.org/10.1029/2022ef002815) assessed that proposal with a radiative transfer model that used (a) HGMs with optical properties published by Field et al., indicating 10% absorption by a thin layer, and (b) hypothetical non-absorbing HGMs. Strawa et al. (2025, https://doi.org/10.1029/2024ef004749) have now obtained updated optical properties indicating that HGMs are less absorptive than previously thought. However, field experiments produce less albedo-enhancement than predicted by radiative transfer models, by 0.1 or more, regardless of which value of HGM absorptance is used in the model.

Plain Language Summary

In 2018, a proposal had been made to spread white powder (tiny glass bubbles) over Arctic sea ice to reflect more sunlight. That proposal was evaluated by Webster and Warren (2022, https://doi.org/10.1029/2022ef002815) using a radiative-transfer model, which predicted that the application of white powder would brighten bare, thin sea ice but would darken snow-covered ice, because a thin layer of glass bubbles absorbs about 10% of the incident sunlight. New laboratory measurements of the glass bubbles by Strawa et al. (2025, https://doi.org/10.1029/2024ef004749) now indicate that the thin layer absorbs only 2.5% of the sunlight. However, field experiments in which the powder is spread over bare, thin ice find less brightening than expected, whichever value of absorption by the glass powder is assumed in the model.

Key Points

Field experiments, in which hollow glass microspheres (HGMs) are spread onto ice, produce less albedo-enhancement than predicted by models

This is true whether the model uses either the original optical properties of HGMs, or the revised values

A method for digitizing printed graphs is described and assessed

Source: AGU