Protesters from Insulate Britain have blocked a junction of the M25 motorway and a major road in central London.
The climate activists said about 40 demonstrators are sitting on the road at junction 25 of the M25 at Waltham Cross, Hertfordshire, and on the A501 at Old Street roundabout.
The protests caused long queues of rush hour traffic on Friday morning.
Insulate Britain admitted its actions on the M25 are “in breach” of an injunction obtained by the Government last month.
Tracey Mallagan, a spokeswoman for the group, said: “If governments don’t act soon to reduce emissions, we face a terrifying situation.
“We won’t be worrying about shortages of pasta or loo rolls because law and order breaks down pretty quickly when there is not enough food to go round.
“The Government won’t be wondering if there are enough hospital beds or ventilators, but whether there are enough people left to bury the dead.
“The Government is destroying our country. Boris Johnson should be taken to court for treason. Our flesh and blood are being tossed aside as expendable.”