The Metropolitan Police has deployed more than 10,000 officers to manage the climate protests in London. (Alastair Grant/AP)

The protesters have snarled traffic on bridges, glued themselves to trains and swung from hammocks in high trees to grab attention. On Tuesday, they descended on Parliament Square to demand that British lawmakers take action to stem climate change.

They got an assist from Greta Thunberg, the teenage Swedish activist who has sparked a global youth movement and led school climate strikes in 100 countries last month.

Thunberg said her generation has been betrayed.

“We probably don’t even have a future anymore,” she said in a speech to lawmakers at Westminster. “That future has been sold so that a small number of people can make unimaginable amounts of money. It was stolen from us every time you said, ‘The sky is the limit.’ ”

Swedish climate activist Greta Thunberg, center, meets Green Party leader Caroline Lucas and Labour Party leader Jeremy Corbyn. (Stefan Rousseau/AP)

Earlier in the day, when asked what she would say to President Trump, who announced that the United States will withdraw from the 2015 Paris agreement to limit carbon pollution, Thunberg replied, “There is nothing I could say.”

“Obviously, he must have scientists coming to talk to him all the time, so he is obviously not listening to the scientists,” she said.

The Metropolitan Police have deployed more than 10,000 officers to manage the climate protests. By Tuesday morning, they had made more than 1,000 arrests and charged 71 people with breaching public order, obstructing traffic or obstructing police.

Demonstrators, who gathered under the banner of the group “Extinction Rebellion,” blocked Waterloo Bridge over the Thames and parked a pink sailboat at the Oxford Circus intersection. They have camped at Marble Arch and staged a “die-in” in the central hall at the Natural History Museum, beneath a skeleton of a blue whale, to raise awareness of the ongoing “mass extinction” brought about by humans. They also took their clothes off during a Brexit debate in Parliament in early April.

Organizers say they have three core demands: for the government to “tell the truth” about climate change; to reduce carbon emissions to net zero by 2025; and to form a citizens assembly to monitor progress. They call the combined assault of habitat loss, species extinction, warming temperatures and sea-level rise an existential threat to humanity and the planet.

Still, Sarah Shurety, a business consultant who came to protest in Parliament Square, said, “I am full of hope.” She carried a letter she wanted to deliver to her representative. It read: “No bees. No flowers. No fruits. No me. No you.”

Shurety said she thought the demonstrations worth the disruption.

“I’ve heard the people who say, ‘Oh, I can’t get to work.’ I think that pales into insignificance [beside] the destruction of the planet,” she said.

London Mayor Sadiq Khan, though, seemed to be reaching the limit of his tolerance. 

“I share the passion about tackling climate change of those protesting, and support the democratic right to peaceful and lawful protest,” he said. “But this is now taking a real toll on our city — our communities, businesses and police. This is counterproductive to the cause and our city.”

Boris Johnson, a former London mayor and a potential future prime minister, said in his column in the Telegraph: “I cannot find it in my heart — no matter how smug, irritating and disruptive they may be — to condemn these protesters today.”

Johnson said he, too, laments the global rise in pollutants and the loss of species. But he said there is reason for cautious optimism — that Britain has been a global leader in carbon reductions.

And in the next few weeks, Johnson wrote, the British government will announce a target of net zero emissions by 2050. 

“That would be an amazing achievement; but the evidence of the last few years is that it can be done, not through hair-shirted Leftyism but solid Tory technological optimism,” he wrote.

In the House of Commons, Labour Party member Ed Miliband said the protesters were right — the government was moving too slowly. “The truth is the planet is warming far faster than we are acting,” he said. “Climate change is not some theoretical future prospect, but is with us here and now.”