The replica suburban house was floated in front of London's Tower Bridge in the early hours of Sunday in an "attempt to send an SOS to the government on climate inaction," the protest group said in a statement.
Extinction Rebellion noted that the ongoing flood disaster in northern England starkly illustrates that "our homes, businesses and families are at very real risk."
"We are watching, in real time, as people's lives are destroyed around the world and in the UK. Unless action is taken to halt biodiversity loss and reduce greenhouse gas emissions to net zero these tragedies are set to worsen," the group said.
The group pointed to scientific predictions that global sea levels could rise between 1 and 5 meters by 2100.
The US National Oceanic and Atmospheric Administration has reported that the global sea levels in 2018 were 3.2 inches (81mm) higher than their 1993 level. It added that 2018 was the seventh year in a row that sea levels had risen over the previous year.