Brief communication: Understanding solar geoengineering's potential to limit sea level rise requires attention from cryosphere experts

Peter J Irvine,David W Keith,John Moore

doi:10.5194/tc-12-2501-2018

Peter J Irvine, David W Keith + Show 1 more

Open Access

https://doi.org/10.5194/tc-12-2501-2018

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Abstract

Abstract. Stratospheric aerosol geoengineering, a form of solar geoengineering, is a proposal to add a reflective layer of aerosol to the stratosphere to reduce net radiative forcing and so to reduce the risks of climate change. The efficacy of solar geoengineering at reducing changes to the cryosphere is uncertain; solar geoengineering could reduce temperatures and so slow melt, but its ability to reverse ice sheet collapse once initiated may be limited. Here we review the literature on solar geoengineering and the cryosphere and identify the key uncertainties that research could address. Solar geoengineering may be more effective at reducing surface melt than a reduction in greenhouse forcing that produces the same global-average temperature response. Studies of natural analogues and model simulations support this conclusion. However, changes below the surfaces of the ocean and ice sheets may strongly limit the potential of solar geoengineering to reduce the retreat of marine glaciers. High-quality process model studies may illuminate these issues. Solar geoengineering is a contentious emerging issue in climate policy and it is critical that the potential, limits, and risks of these proposals are made clear for policy makers.

Highlights

A rapid transition towards a carbon-free economy will reduce additional temperature increases but the temperature response to cumulative emissions – and the impact on sea level – will remain for millennia without measures beyond emissions cuts (Clark et al, 2016)
Here we focus on stratospheric aerosol injection and unless otherwise stated, solar geoengineering will hereafter refer to stratospheric aerosol geoengineering only
This study aims to highlight the key questions around the sea level rise response to solar geoengineering that only the sea level and cryosphere community will be able to resolve

Summary

Future sea level rise and the potential of solar geoengineering

How far sea levels would rise under some scenario of future climate change depends mainly on global temperature rise, and uncertainties in projections rise rapidly as warming increases more than 2 ◦C above preindustrial conditions (Jevrejeva et al, 2016; Kopp et al, 2014). Under scenarios in which solar geoengineering halts regional temperature increases, 30 % of present-day glaciated area will still be lost this century due to the glaciers being out of balance with present-day climate These studies illustrate that if solar geoengineering were deployed it could reduce the rate of sea level rise substantially compared with greenhouse forcing alone. They note that insolation changes result in relatively larger changes in net radiative fluxes at the surface than CO2 forcing, resulting in larger changes in sensible and latent heat fluxes Beyond this fundamental difference in the climate response to solar forcing, some stratospheric aerosols, sulfuric acid, the most important single proposal, have significant near-infrared absorption bands that would result in a warming of the stratosphere. We will identify how solar geoengineering could affect these factors and identify the most pressing uncertainties

Response of sea level rise to solar geoengineering

Thermosteric sea level rise

Surface mass balance

Ice shelf collapse and dynamic mass loss

Findings

Recommendations for research