The World Heritage Committee (WHC) has rejected a motion calling for cuts in greenhouse gas emissions.
Protection has been sought for two of the world's major coral reefs
The WHC meeting in Lithuania heard evidence that 125 sites including the Himalayas and the Great Barrier Reef are at risk from climate change.
Campaigners wanted the WHC to agree that the only way to protect such sites was by reducing emissions, which would have obliged governments to make cuts.
But in discussions on Monday this option was rejected by the Unesco body.
A further clause encouraging countries to draw on projections from the Intergovernmental Panel on Climate Change (IPCC) when assessing risks to World Heritage Sites was also rejected.
Environmental campaigners have reacted with frustration, and blamed the move on lobbying by governments opposed to restrictions on greenhouse gas emissions.
"We are extremely angry that the World Heritage Committee has not taken any meaningful action to protect some of the most important sites on Earth from climate change," said Peter Roderick, co-director of the Climate Justice Programme.
"They are good at drawing up wonderfully drafted documents, but the idea of actually doing anything seems to pose a problem.
"The world is entitled to expect better from the Committee; bending over backwards as a result of fear of the US and Canada will tarnish its reputation."
Two years ago, Climate Justice co-ordinated petitions from environmental groups saying that three World Heritage Sites - Sagarmatha National Park in the Himalayas, Huascaran National Park in Peru and the Belize Barrier Reef - were being irreparably damaged by the impacts of human-induced global warming.
The Sagarmatha petition was backed by Everest pioneer Sir Edmund Hilary.
The Tower of London is one of the sites considered to be threatened
Subsequent petitions were lodged concerning the Waterton-Glacier International Peace Park on the US-Canada border and Australia's Great Barrier Reef.
A survey conducted by the World Heritage Committee among its member nations found that 125 sites are threatened by climate change.
These include the Tower of London which could be damaged by rising sea levels.
"The survey by the World Heritage Committee suggests that climate change is already impacting on scores of the world's most spectacular natural heritage sites," said Catherine Pearce, climate campaigner for Friends of the Earth International.
"Unless the international community takes urgent action to cut their emissions of greenhouse gases the situation will get much worse."
The WHC meeting, in the Lithuanian capital Vilnius, runs until 16 July.