Environmental consultant Dr Andrew Boswell, former Norfolk county councillor, joined activists at Marble Arch and said any inconvenience people experienced as a result of the two week protest was insignificant in comparison to the "catastrophic impact" of climate change.
The group has called on the United Kingdom government to reduce carbon emissions to zero by 2025 and establish a citizens' assembly to devise an emergency plan of action to tackle climate breakdown and biodiversity loss.
Parliament Square, Marble Arch, Waterloo Bridge and Piccadilly Circus were also targeted - with Waterloo Bridge seeing the addition of a skater's half-pipe and trees.
Workers at Shell were prevented from leaving the building after members of Extinction Rebellion superglued themselves to the entrance of their office, just before lunchtime too.
Hundreds of protesters had also blocked Waterloo Bridge, which was closed in both directions, with campaign group Extinction Rebellion declaring on their Twitter page: "We have taken Waterloo Bridge!"
The protest had a festive atmosphere, with many families in attendance, and a low police presence.
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The group tweeted: "Day 1 of #InternationalRebellion saw actions in 33 countries, 52 willing arrests in London occupations of #MarbleArch #OxfordCircus #ParliamentSquare #WaterlooBridge #PicadillyCircus, overnight some occupations evicted". "In the majority world, indigenous communities are now on the brink of extinction".
Extinction Rebellion said: "We've tried petitions, marches, letters, reports, papers, meetings, even direct actions; and global emissions have continued to rise. We must act now".
London's police have advised people travelling around London in the coming days to allow extra time for their journey in the event of road closures and general disruption.
The campaign group said that "over 100 courageous rebels" had been arrested, some willingly.
Thousands of environmental protesters will converge on London today in a bid to "shut down" the capital and force the government's hand on climate change.