Insulate Britain have returned and blocked roads in three locations across London with the police saying they are on the scene to deal with the protesters.
In a statement, Insulate Britain said that after a 10-day break 61 people blocked three locations across the capital including Upper Thames Street, Bishopsgate and Limehouse Causeway in Canary Wharf - all main routes in and around the city.
Traffic on Bishopsgate was brought to a halt as protesters blocked the road at the junction of Camomile Street.
Protesters also began supergluing themselves to the ground.
One woman who first glued her hand down was taken away by police and as she was released, she screamed and said she was "in agony".
Buses and other vehicles were held up as activists sat in the road at the traffic lights.
Drivers were handed a notice from the protesters which read: "Dear driver, we are peaceful and non-violent. We are sorry to delay your journey.
"For your safety please stay in your vehicle and do not drive on the hard shoulder. This is for emergency vehicles.
"The police are on their way. They will arrest us and you will be able to continue your journey."
Tony Hill, 71, who travelled from near Kendal in Cumbria to join the protest, said Insulate Britain's call to insulate all UK homes was a "no brainer".
Members of the public heckled protesters blocking the roads.
One man, who shouted as he walked by, said: "We all have jobs to go to."
Another walked up to the protesters, looked down and said: "What are you doing in the middle of the road. I can't get to work."
It is the 14th time Insulate Britain has caused disruption on motorways and A roads as part of its campaign.
The City of London Police tweeted to say they were aware of the disruption.
They said: "Bishopsgate is currently closed at the junction with Wormwood Street due to protest activity. Police are at the scene but please avoid the area if possible as this is causing disruption to traffic."
Officers also said that they were at "Southwark Bridge at the junction with Upper Thames Street", which is closed in both directions due to protest activity.
In the statement, activist Liam Norton branded the government "treasonous", claiming it had "betrayed" citizens.
He said: "We know that the public is frustrated and annoyed at the disruption we have caused.
"They should know that one way or another this country will have to stop emitting carbon. We can do that now in an orderly, planned way, insulating homes and preventing thousands of deaths from fuel poverty, or we can wait until millions have lost their homes and are fighting for water or starving to death."
Insulate Britain, an offshoot of Extinction Rebellion, wants the government to insulate all UK homes by 2030 to cut carbon emissions.
It blocked roads on 14 days over the five weeks to 14 October, with activists often gluing their hands to the carriageway to increase the length of time it takes for police to remove them.
Hundreds of arrests were made, with some people detained several times.
The campaign continues despite injunctions leaving protesters facing court summons and possible imprisonment or an unlimited fine.