Seaweed carbon removal cannot keep up with climate-driven loss.

The prevailing narrative of seaweed carbon as a possible climate change mitigation solution overlooks the central challenge that climate change itself is adversely impacting seaweed forests worldwide, potentially shifting these ecosystems from carbon sinks to carbon sources. In this Essay, we show that climate-induced seaweed forest loss is eroding their carbon sink capacity three to four orders of magnitude (1,000-10,000×) faster than it can currently be restored or recovered through active interventions. We consider that this stark disparity calls for a fundamental shift in seaweed carbon research away from a focus on future sequestration gains and toward explicitly assessing the risk of carbon emissions from climate-driven ecosystem loss.