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.
"We may be close to passing a tipping point for at least some of the large outlet glaciers draining the West Antarctic Ice Sheet, and this would commit us to significant sea level rise whatever we decide in terms of reducing greenhouse gas emissions," Stephan Harrison, professor of climate and environmental change at the University of Exeter, said in the statement.
Katey Burak and Rob Higgs, who built the house, said they wanted to "respectfully raise awareness of the severity of the impending human-made disaster," noting that climate change "affects every one of us."
"We wanted to make something that people can visually connect to, whilst leaning on the government and the experts to make the changes that need to be made," they said.
Extinction Rebellion accused Britain's Prime Minister Boris Johnson of not considering widespread flooding to be a national emergency. The group warned, in contrast, that many people in low-lying areas across Britain will be affected by flooding this coming winter.
"We stand in solidarity with all of those who have lost their homes and livelihood and will continue to demand action until the severity of this national and global emergency is realized," it said.
Extinction Rebellion protesters have carried out several demonstrations in the British capital, including a two-week campaign of civil disobedience in October.
London's Metropolitan Police issued a revised Section 14 order when thousands of protesters took to the city's streets, imposing a four-day ban prohibiting any assembly of more than two people linked to the October protests dubbed the "Autumn uprising."
The police's decision was overturned this month, with the London high court ruling that the ban was "unlawful."