1. Warming world, changing ocean

Summary

Proactive and coordinated action to mitigate and adapt to climate change will be essential for achieving the healthy, resilient, safe, sustainably harvested and biodiverse ocean that the UN Decade of Ocean Science and sustainable development goals (SDGs) seek. Ocean-based mitigation actions could contribute 12% of the emissions reductions required by 2030 to keep warming to less than 1.5 °C but, because substantial warming is already locked in, extensive adaptation action is also needed. Here, as part of the Future Seas project, we use a ‘‘foresighting/ hindcasting’’ technique to describe two scenarios for 2030 in the context of climate change mitigation and adaptation for ocean systems. The ‘‘business-asusual’’ future is expected if current trends continue, while an alternative future could be realised if society were to effectively use available data and knowledge to push as far as possible towards achieving the UN SDGs. We identify three drivers that differentiate between these alternative futures: (i) appetite for climate action, (ii) handling extreme events, and (iii) climate interventions. Actions that could navigate towards the optimistic, sustainable and technically achievable future include: (i) proactive creation and enhancement of economic incentives for mitigation and adaptation; (ii) supporting the proliferation of local initiatives to spur a global transformation; (iii) enhancing proactive coastal adaptation management; (iv) investing in research to support adaptation to emerging risks; (v) deploying marine-based renewable energy; (vi) deploying marine-based negative emissions technologies; (vii) developing and assessing solar radiation management approaches; and (viii) deploying appropriate solar radiation management approaches to help safeguard critical ecosystems.