The Prince of Wales said climate change was "the greatest challenge to face mankind" as he visited a nature reserve in Wiltshire.
Prince Charles stressed the "need to reduce urgently the amount of carbon dioxide released into the atmosphere".
With his wife, the Prince visited Lower Moor Farm, where they declared a new visitor centre open, planting orchids to mark the occasion.
The farm is owned by Wiltshire Wildlife Trust and is a habitat for wildlife.
In his speech, the Prince said the UK needed more large swathes of land like the farm, rather than small, isolated corners in between intensively farmed areas.
"Our landscapes are not fit to cope any more," he said.
"Small, isolated pockets of land can no longer provide the protection needed for our wildlife."
On Lower Moor Farm is Mallard Lake, one of two lakes in Wiltshire which are sites of special scientific interest.
The lake contains a population of stoneworts, which thrive in clean water.