Rising sea levels could result in towns and villages along the Suffolk and north Essex coast being below the flood level by 2050, it has been projected.
Independent group Climate Central, which researches and reports on the climate crisis, has developed a map of which areas could face regular flooding in less than 30 years.
But the Environment Agency has called the group's prediction "inaccurate and unsuitable to inform local coastal flood risk".
Climate Central's projection comes after a UN report warned that humans are unequivocally driving global warming.
The map has used data from peer-reviewed scientific papers to predict the coastal areas that could be below the annual flood level in 2050.
The Environment Agency said it was investing more than £90million into reinforcing flood defences across East Anglia, including in Lowestoft.
An Environment Agency spokesman said Climate Central's data "does not take into account extensive efforts taken to prevent such severe incidents in the future, including the presence of sea defences, which protect communities from flooding".
In its information about its map, Climate Central said: "As these maps incorporate big datasets, which always include some error, these maps should be regarded as screening tools to identify places that may require deeper investigation of risk."
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