A Just Stop Oil activist filmed a video in tears from the top of a 275ft bridge after his protest saw traffic on the M25 grind to a halt.
Essex Police closed the Queen Elizabeth bridge in Dartford to thousands of drivers in the early hours of Monday morning.
Morgan Trowland, 39, was overcome with emotion as he spoke into the camera, saying he did not want to "sit back and watch everything I love burn for the rest of my life."
The protests are an attempt to force the UK to commit to renewable energy.
Civil engineer Mr Trowland, who launched the protest movement along with fellow demonstrator Marcus, a 33-year-old teacher from London, scaled the structure and flew a banner reading Just Stop Oil.
In his message from the top of the huge bridge, he said: "I have climbed up this cable of the QEII bridge of the M25.
"It has been really difficult to grip into this cable... I am willing to do this because I am not willing to sit back and watch everything I love burn for the rest of my life and that’s whats happening.
"The current fraudulent charlatan excuse we have for a government is accelerating that process and granting licenses for more gas"
Mr Trowland said it was an "absolute act of treason" by the government, adding: "Selling all of ourselves and our children to an uninhabitable earth and I believe it's my duty to do anything in my power to stop it.
"So my friend and I have climbed up here today. We are going to stay here until the gov makes a meaningful statement that they will end new licensing consents... and they will start an emergency transition to the renewable energy we need. "We are out of time, please join the resistance."
Essex Police said the bridge was closed to traffic shortly before 3.50am this morning.
Mr Trowland said: "As a professional civil engineer, each year as I renew my registration, I commit to acting within our code of ethics, which requires me to safeguard human life and welfare and the environment.
"Our government has enacted suicidal laws to accelerate oil production: killing human life and destroying our environment.
"I can't challenge this madness in my desk job, designing bridges, so I'm taking direct action, occupying the QE2 bridge until the government stops all new oil."
Just Stop Oil said in a statement the disruption was likely to continue to 24 hours, saying: "Two Just Stop Oil supporters have climbed to the top of the Queen Elizabeth II Bridge forcing police to close the bridge to demand that the government halts all new oil and gas licences and consents,' it said.
"At approximately 5am two climbers ascended the two 84m masts on the north side of the Queen Elizabeth II Bridge forcing the police to stop traffic from entering the bridge. It is expected that the bridge will remain shut for at least 24 hours."
A spokesperson from Essex Police said: "Officers are currently working to resolve a situation which has caused us to close the QEII Bridge at the Dartford Crossing.
"We received a report shortly before 3.50am today (Monday 17 October) that two people had climbed onto the bridge and are currently at height.
"The bridge has been closed while we resolve the incident which we will do as quickly and as safely for all involved."
Chief Constable Harrington said he thought the pair were 'crazy' and was firmly on the side of motorists.
Speaking to BBC Essex, he said: "We want them to come down, but we've got to do that safely. Safely for the public, safely for the people who use the bridge and safely for those who operate the bridge. It's a really dangerous and difficult environment.
"I think they are crazy. I'm really frustrated and you've got every guarantee from me that the officers there at the moment, working with the Dartford Crossing and National Highways, will get that road open as soon as possible."
The 2.8km-long (1.7 mile) QEII bridge southbound, and two 1.4km-long (0.8 mile) tunnels northbound link Essex and Kent.
The A282 also connects directly at both ends with the M25 London Orbital Motorway, one of the busiest motorways in Europe.
Police said colleagues at National Highways are escorting traffic through the Dartford Tunnel in a bid to alleviate the impact of the road closure.
