Estimating the potential cooling effect of cirrus thinning achieved via the seeding approach

Cirrus thinning is a newly emerging geoengineering approach to mitigate global warming. To sufficiently exploit the potential cooling effect of cirrus thinning with the seeding approach, a flexible seeding method is used to calculate the optimal seeding number concentration, which is just enough to prevent homogeneous ice nucleation from occurring. A simulation using the Community Atmosphere Model version 5 (CAM5) with the flexible seeding method shows a global cooling effect of -1.36 +/- 0.18 W m(-2), which is approximately two-thirds of that from artificially turning off homogeneous nucleation (-1.98 +/- 0.26 W m(-2)). However, simulations with fixed seeding ice nuclei particle number concentrations of 20 and 200 L-1 show a weak cooling effect of -0.27 +/- 0.26 W m(-2) and warming effect of 0.35 +/- 0.28 W m(-2), respectively. Further analysis shows that cirrus seeding leads to a significant warming effect of liquid and mixed-phase clouds, which counteracts the cooling effect of cirrus clouds. This counteraction is more prominent at low latitudes and leads to a pronounced net warming effect over some low-latitude regions. The sensitivity experiment shows that cirrus seeding carried out at latitudes with solar noon zenith angles greater than 12 degrees could yield a stronger global cooling effect of -2.00 +/- 0.25 W m(-2). Overall, the potential cooling effect of cirrus thinning is considerable, and the flexible seeding method is essential.

Automated summary

Cirrus thinning is a new geoengineering approach that can provide considerable cooling effects, with the flexible seeding method being essential for optimal results. However, fixed seeding ice nuclei particle concentrations may result in weaker effects.