Current and projected global extent of marine built structures

Marine construction is sprawling globally. As of 2018, this study finds that the structures occupied 32,000 km(2)but affected 1 to 3 million km(2), a shadow expected to expand 50-70% by 2028. The sprawl of marine construction is one of the most extreme human modifications to global seascapes. Nevertheless, its global extent remains largely unquantified compared to that on land. We synthesized disparate information from a diversity of sources to provide a global assessment of the extent of existing and projected marine construction and its effects on the seascape. Here we estimated that the physical footprint of built structures was at least 32,000 km(2)worldwide as of 2018, and is expected to cover 39,400 km(2)by 2028. The area of seascape modified around structures was 1.0-3.4 x 10(6) km(2)in 2018 and was projected to increase by 50-70% for power and aquaculture infrastructure, cables and tunnels by 2028. In 2018, marine construction affected 1.5% (0.7-2.4%) of global Exclusive Economic Zones, comparable to the global extent of urban land estimated at 0.02-1.7%. This study provides a critical baseline for tracking future marine human development.