Half-Earth Journal Article Anthromes Bonn challenge Comment Convention on Biological Diversity Global Human Modification Human Footprint Letter Low Impact Areas Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. Sustainable Development Goals connectivity conservation planning conservation targets cumulative impact assessment ecological integrity habitat intactness habitat restoration human footprint human influence intermediate disturbance land use policy landscape fragmentation threshold landscape gradient protected areas spatial conservation prioritization wilderness