Days after thousands of demonstrators shut down major central London bridges to demand bold climate action from world leaders, environmentalists and members of the Extinction Rebellion movement were back in the streets again on Wednesday highlighting the world's "ecological emergency" and calling for immediate steps toward the goal of reducing carbon emissions to net zero by 2025.

"Standing up to save humanity from extinction is not criminal, it's the only sane thing we can do."

—Donnachadh McCarthyWhile politely apologizing for the major traffic disruptions caused by the demonstrations, Extinction Rebellion declared in a statement that "this relatively minor inconvenience could save us all from catastrophic consequences in years to come."

"I think it's going well—a little light disruption to raise awareness of the biggest threat to our future, climate change," said Josie, a 23-year-old activist from Bristol. "We need to do everything we can to spark some thoughts, plant some seeds, and also—it's just good to be part of this community—to act and resist together. We are planting seeds to grow some new ideas."

"Standing up to save humanity from extinction is not criminal, it's the only sane thing we can do," added author and activist Donnachadh McCarthy.

Aiming for "gridlock across the capital," Wednesday's demonstrations took place at major traffic hot spots in London such as Vauxhall Bridge and Earl's Court.

"To those inconvenienced by the climate change roadblocks in London, we've tried all other options," activist Hannah Scott wrote on Twitter. "The scientists have yelled at us for decades. Civilized negotiations with governments. Greening capitalism. Not enough. Sorry but we have no other option. "

Demonstrations and disruptions across London demanding urgent climate action are expected to continue for the rest of the week, culminating in "Rebellion Day 2" on Saturday in Parliament Square.

Dr. Larch Maxey, research fellow at the University of Plymouth, said in a statement that he has been "really amazed" by how effective the mass demonstrations have been thus far.

"It is clearly causing a lot of economic disruption which is what you have to do to get the government to listen," Maxey said. "In terms of reaction from people, when they hear that this is about climate change they understand. We’ve had so many people thanking us, even had a high-five."