Evidence that marine conservation mitigates climate change

"Marine protected areas are increasingly being promoted as an ocean-based climate solution. Yet such claims remain controversial due to the diffuse and poorly synthesized literature on climate benefits of marine protected areas," write the authors. "To address this knowledge gap, we conducted a systematic literature review of 22,403 publications spanning 241 marine protected areas."

The authors found that carbon sequestration in marine protected areas increased significantly in seagrass areas, mangroves, and in areas where sediment wasn't trawled. "Partial or full degradation of mangroves and seagrass both resulted in similar decreases of sequestered carbon, indicating that even low levels of human impact result in important carbon emissions," they write.

In addition to boosting carbon sequestration, preserved areas were more biodiverse, had increased species richness, and showed benefits for humans, too. Marine protected areas had greater food security, and fish stocks in waters adjacent to these protected areas swelled. The authors note that the mitigation and adaptation benefits of these protected areas were only achieved under high levels of protection, and that benefits increased the longer an area had been protected.

"Across all four pathways analyzed, only full and high levels of protection resulted in mitigation or adaptation benefits," they write. "In contrast, low levels of protection generated no benefits. Furthermore, increases in species richness and in fishers' income only occurred for fully protected areas, where no fishing is allowed."