Wales has been urged to take "urgent action" to prepare for the impact of coastal erosion and flooding.
The National Trust says three-quarters of the Welsh coastline it owns could be badly affected over the next century.
It owns a sixth of Wales' coast, or over 143 miles (230km), and its report, Shifting Shores, says policymakers must plan for "a future of advancing seas".
Environment Minister Carwyn Jones said it was "entirely consistent" with the Welsh Assembly Government's approach.
The National Trust In Wales warns that 66 coastal sites covering 1,572 hectares are at risk of flooding in the next 100 years.
By that time, some experts predict that sea levels will rise by a metre (3ft 3in) and climate change will lead to more severe storms.
Internationally-recognised sites which could be under threat include the Stackpole Estate in Pembrokeshire, Cemlyn Lagoon on Anglesey - an important wildlife site - dune systems on the Gower peninsula near Swansea and historic sea forts like Dinas Dinlle in Gwynedd.
Beaches including Marloes in Pembrokeshire may disappear, it warns, while features like coastal footpaths will need to be moved inland.
Shifting Shores highlights issues to be addressed by the assembly government's plans for adapting to climate change and forthcoming legislation for the marine environment.
The NT said it wanted a fresh approach, with "urgent action to put in place coherent, long-term planning to address the massive impacts of future sea level rise".
Iwan Huws, director of National Trust Wales, said: "The challenges facing the National Trust provide a snapshot of how sea level rise and climate change will affect the whole of Wales.
"We have started to prepare for and adapt to the changing nature of the coastline, something that all levels of government and government agencies in Wales should be focussing on now as part of a co-ordinated response to climate change.
NATIONAL TRUST COAST STRATEGIES
Raising public awareness and understanding
Simplifying decision-making with agencies and authorities in coastal management
Moving with the coast and the forces of nature
Finding new financial mechanisms - eg insurance and compensation to allow vulnerable communities to adapt
"No-one in Wales is more than 50 miles from the shore, and tourism is particularly dependent on our wonderful coast.
"Like King Canute, we can't control the ocean and command it to retreat. Instead, we must plan how to adapt to a future of advancing seas. The first step is to raise awareness of what is at stake."
Mr Huws said the changing coastline demonstrated that the impact of climate change was being felt "here and now".
"This should strengthen the call to reduce our carbon footprint, but we also need to adapt to the changes underway and plan for the future of coastal communities."
Environment Minister Carwyn Jones said the report's key messages were "very much in line with assembly government thinking".
"The future challenges we face in managing our coastline will be considerable.
"Successful management will require strong leadership, close collaboration and hard choices.
"If we are to succeed then we will need to think innovatively in terms of how we manage our coastline and ensure that we engage the whole of society in the process," said Mr Jones.
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