The number of UNESCO natural sites at risk has grown to 62 from 35 in 2014, when one in seven were listed, according to the International Union for Conservation of Nature (IUCN), which released the report at UN climate talks in Bonn, Germany.
Among the ecosystems most threatened by global warming are coral reefs which bleach as oceans heat up, and glaciers which melt.
"Climate change acts fast and is not sparing the finest treasures of our planet," said IUCN director general Inger Andersen.
The report found that 29 per cent of UNESCO natural sites faced "significant" threats, and seven percent -- including the Everglades National Park in the United States and Lake Turkana in Kenya -- had a "critical" outlook.
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"The scale and pace at which it (climate change) is damaging our natural heritage underline the need for urgent and ambitious national commitments and actions to implement the Paris Agreement," said Andersen.
The agreement seeks to limit average global warming caused by greenhouse gases from fossil-fuel burning to under two degrees Celsius (3.6 degrees Fahrenheit) over pre- industrial levels, and to 1.5 C if possible.
The 1 C mark has already been passed, and scientists say that on current country pledges to cut emissions, the world is headed for a 3 C future.
The IUCN monitors more than 200 natural Heritage Sites listed by the UN Educational Scientific and Cultural Organisation (UNESCO).
Corals "bleach" when they are stressed by environmental changes -- due to ocean warming or pollution.
The corals expel the colourful algae that live in them, and turn bone white.