PNNL

Abstract

Marine Cloud Brightening (MCB) refers to the deliberate injection of aerosol particles into shallow marine clouds to increase their reflection of solar radiation, with the intent to temporarily offset planetary warming while decarbonization efforts are being pursued. A review and assessment of existing knowledge of the topic points to gaps in our understanding and a need for refinement of laboratory experiments, observations, and modeling tools to address the gaps. A consensus viewpoint is the need for routine field activities tightly coordinated with modeling and satellite remote sensing to test critical components of proposed MCB activities. Such an effort would cover activities ranging from particle generation and delivery to clouds; local detection of cloud brightening; regional responses; and global assessments of radiative forcing. We raise the idea of a bespoke targeting of the more limited set of clouds that are most likely to produce cloud brightening. While this is more physically appealing than a routine, ‘one-size-fits-all’ seeding, it might suffer from a more challenging implementation and a reduced frequency of cloud targets. The potential for success of MCB will ultimately depend crucially on observations and models that can assess robustly the scale-up of local-to-global brightening in the present-day climate and identify strategies that will avoid an inequitable geographical distribution of benefits and damages. A substantial and targeted program of research — including field and laboratory experimentation, monitoring, and numerical modeling across a range of scales — is required to refine our understanding of the physical science issues, so that the societal implications of an MCB program can be soundly assessed.