My #dataviz -adjacent hot take: Ordinary people don't have a sense of scale for area units that aren't m^2 or sqft (in USA). Too often km^2 is confused with 1000 m^2. Hectares/acres are nebulous too.
My solution: don't measure area in football fields or Californias - just present equivalent square side length.
For instance: Denmark will reforest 4000 km^2 of its presumably least productive farmland. This would be a 63x63 km square.