Where to now? A synthesis of current views of the CLAW hypothesis

The CLAW hypothesis was published 20 years ago, building on suggestions that the sulfur cycle provided a natural feedback mechanism whereby plankton in the ocean had a role in modifying climate by providing the precursors for cloud condensation nuclei, which leads to the formation of high albedo clouds. In this issue, the 10 preceding articles represent the opinions of several leading scientists working on various aspects of the CLAW hypothesis and here we synthesise these varied opinions to answer the questions: Does the CLAW hypothesis operate as described in the original 1987 publication? and What steps and advances are needed to better understand CLAW and resolve any outstanding areas of difficulty?