Protesters spoke out against Heathrow expansion and coal power stations
Dozens of cyclists blocked a London bridge in protest at the government's environmental policies.
Some members of group Climate Rush held picnics on Westminster Bridge in the sit-in near the Houses of Parliament.
Protester Rob Faure Walker, 27, a teacher from north London, said the government was failing "in any way" to plan to reduce carbon emissions.
There were no arrests in the Monday night protest. The Department for Environment was unavailable to comment.
Many protesters wore red sashes bearing the slogans "Trains Not Planes" and "No To New Coal".
Mr Faure Walker spoke out against the building of new coal-fired power stations and the expansion of Heathrow airport.
"People have to realise that they can't live their lives the way that they have become accustomed to," he said.
"We can't fly short-haul whenever we want."
The bridge was subsequently reopened to traffic as the protesters remounted their bicycles and rode off.
In April four members of Climate Rush glued themselves to a statue inside the Houses of Parliament.