Tidal flat

Sediment

Global change

Ecology

Marsh

Biology

Wetland

Intertidal zone

Computer science

Salt marsh

Geology

Oceanography

Paleontology

Offset (computer science)

Global warming

Climate change

Environmental science

Mangrove

Programming language

Ecosystem

Science

Tidal wetlands are expected to respond dynamically to global environmental change, but the extent to which wetland losses have been offset by gains remains poorly understood. We developed a global analysis of satellite data to simultaneously monitor change in three highly interconnected intertidal ecosystem types—tidal flats, tidal marshes, and mangroves—from 1999 to 2019. Globally, 13,700 square kilometers of tidal wetlands have been lost, but these have been substantially offset by gains of 9700 km 2 , leading to a net change of −4000 km 2 over two decades. We found that 27% of these losses and gains were associated with direct human activities such as conversion to agriculture and restoration of lost wetlands. All other changes were attributed to indirect drivers, including the effects of coastal processes and climate change.

High-resolution mapping of losses and gains of Earth’s tidal wetlands