In terms of the financial risk, the study says that Miami could have $3.5 trillion of assets exposed to coastal flooding by 2070, with Guangzhou, China, facing exposure of $3.4 trillion.
"We are facing a head on collision between the growth of coastal urban areas and climate change which makes coastal flooding more likely," Alison Doig, principal climate change advisor for Christian Aid and the report's author, said in a statement.
"This perfect storm is likely to bring about a heavy human and financial toll unless we do something about it," Doig added.
The report comes hot on the heels of data from NASA which shows that this April was the hottest on record.
Only last week, the National Oceanic and Atmospheric Administration said that between January and April this year the contiguous United States had an average temperature that was four degrees Fahrenheit "above the 20th century average, making this period the second warmest on record."
For Christian Aid's Doig, while there is clear cause for concern, work can still be done to mitigate impacts. "There is a chance this horrifying vision of the future can be avoided," she said.
"It is striking that the cities facing the most severe impacts are in countries with high contributions of carbon emissions. The first thing we can do is speed up the global transition away from dirty fossil fuels to the clean, renewable energy of the future."
Hastening the transition to renewables as well as increased spending "on reducing the risk of disasters" would also save money and lives, Doig said.