In December 2019, the European Commission announced The European Green Deal, a plan to facilitate a transition to sustainability with the goal of making Europe climate neutral by 2050 (1). Green Deal objectives include preserving and restoring biodiversity and reducing net emissions of greenhouse gases (1). The EU Parliament adopted a resolution supporting these environmental goals in January (2). Lisbon, Portugal’s capital, has been designated the European Green Capital 2020 for spearheading sustainability efforts (3). However, Lisbon’s airport has reached capacity, and plans to build an additional airport are at odds with Green Deal objectives.

The proposed location for the new airport is a peninsula at the heart of the Tagus estuary (4), a vast coastal wetland of key importance for breeding, wintering, and passing migratory birds in the East Atlantic Flyway (5, 6). This wetland is a major hub linking Palearctic and Nearctic breeding areas with Afro-tropical wintering areas for an estimated 300,000 waterbirds and many other migratory bird species. The region is protected under national legislation, EU directives, and international conventions (5–7). However, the privately funded proposed airport received an environmental license in early 2020 (8), and, despite the aviation sector facing unprecedented reductions in activity due to the coronavirus disease 2019 (COVID-19)