Parallel and diverging responses across four Earth system models in response to cirrus cloud thinning climate intervention experiment

[Geoengineering News]

https://iopscience.iop.org/article/10.1088/2752-5295/ae8c7a/meta

Authors: William McFarlane Smith, Daniele Visioni, Ben Kravitz, Evelien van Dijk, Trude Storelvmo and Hugh Hunt

17 July 2026 

DOI 10.1088/2752-5295/ae8c7a

Abstract

Cirrus clouds have a net warming effect on Earth's climate. It has been positioned that deliberately thinning these clouds by seeding them with ice nucleating particles could, to some extent, counter anthropogenic global warming by allowing more longwave radiation to escape to space. This climate intervention technique is known as cirrus cloud thinning (CCT). In this work, CCT has been simulated in four Earth System Models (ESMs) - UKESM, IPSL, GISS and NorESM - by increasing the sedimentation velocity of cloud ice crystals by a fixed amount under a background of SSP5-8.5 (a high emissions scenario). This experiment, proposed as part of the Geoengineering Model Intercomparison Project (GeoMIP), was intended to explore the climatic response to CCT with a simplified methodology in order to obtain more consistent results across different ESMs. Across all four ESMs, we find a global mean cooling relative to the background scenario of -0.42 K to -0.93 K by the middle of the century and increases in precipitation. Although all ESMs do exhibit the expected cooling as a result of a reduction in cloud cover in the upper troposphere, they diverge in the responses of lower cloud coverage, humidity, and hydrological cycle. This divergence shows that there are different processes that lead to forcing at play in the models, highlighting the need for better representation of cirrus clouds and their radiative impacts.

Source: IOP Science