Jon Egill Kristjansson, University of Oslo
As global anthropogenic emissions of greenhouse gases continue to rise, there is an increasing risk of serious disruptions in ecosystems due to global warming. As a consequence, research on climate engineering (CE) is receiving growing attention, also among climate scientists. But, even basic CE research using Earth System Models (ESMs) raises a series of ethical questions that need to be considered. Also, CE carries a risk of serious side effects, e.g., concerning the hydrological cycle.
Climate engineering can be divided into Greenhouse Gas Removal and Radiation Management (RM) techniques. RM here refers to the deliberate modification of either incoming solar radiation or outgoing terrestrial radiation. We will review the basic principles of four proposed RM techniques – stratospheric sulfur injections, marine sky brightening, cirrus cloud thinning and desert brightening. We then present recent robust results concerning changes to the hydrological cycle from multi-model ESM experiments within the Geoengineering Model Intercomparison Project (GeoMIP).
We show that the changes in the hydrological cycle depend strongly on which RM technique is applied. For instance, cirrus cloud thinning influences the hydrological cycle in a distinctly different way than techniques that reduce incoming solar radiation. We will demonstrate how that finding can be explained from atmospheric energy budget considerations.