Big climate change protests are currently taking place across the UK and other European cities.
An activist group call the Extinction Rebellion are behind the demonstrations in the UK.
The group are using non-violent gatherings to encourage the British government to take action on climate and environment issues.
Protests have been going on in the centre of London for five days now, with no confirmation on when they will end.
They have also caused problems for people in the capital trying to use public transport.
Police have arrested hundreds of people involved in the protests.
Who are they?
The Extinction Rebellion describe themselves as: "An international apolitical network using non-violent direct action to persuade governments to act on the Climate and Ecological Emergency."
The group led their first big protest last year in Parliament Square in London, 1,500 people turned up.
Over the course of a week they carried out a series of peaceful protests, including planting trees and blocking bridges.
Actress Emma Thompson, who played Nanny McPhee, has also joined on 19 April, after flying back from Los Angeles in America.
She said: "It makes me so happy to be able to join you all and to add my voice to the young people here who have inspired a whole new movement."
She also said that her generation had: "failed young people".
What do they want?
The activist group have three demands which they want the government to take action on.
- These are to "tell the truth" by declaring a "climate and ecological emergency" and work together with other institutions to help spread the message for the need for change.
- Secondly, the UK must "act now" to stop loss of habitat and reduce carbon emissions to net zero by 2025.
- The third demand is the formation of a Citizens' Assembly to "oversee the changes" that will be needed to achieve this goal.
What have they been doing?
So far, protesters have glued themselves to trains, chained themselves outside politicians houses and planted trees on Waterloo Road in London.
A small group of activists also protested at Heathrow Airport, causing delays to some flights.
A pink boat has become a focal point in the middle of a busy shopping street in London, Oxford Circus, where people have been giving speeches.
Why has this caused problems?
The big crowds have caused blockages to roads, as well as delays to public transport and flights.
Home Secretary Sajid Javid said the climate activists had "no right to cause misery" and the Met Police "must take a firm stance".
Ken Marsh, chairman of the Metropolitan Police Federation, said: "This is very, very difficult for us because my colleagues have never come across the situation that they are faced with at the moment."
"They are dealing with very, very passive people, probably quite nice people, who don't want confrontation whatsoever with the police or anyone else but are breaking the law."
Some critics have said that the group's demands are unrealistic.
Researchers at the Centre for Alternative Technology have said that it would be a huge challenge to get to zero emissions by 2025 but that they support ambitious goals.
Flights would have to be very strictly restricted, as well as people changing what they eat by cutting back on meat and dairy.
In order to get enough renewable energy to replace gas boilers, Britain would need thousands of extra wind turbines.
What else is happening around the world?
Climate change protesters in Paris blocked the entrance of the Societe Generale bank headquarters, as well as the headquarters of French oil giant Total.
Swedish schoolgirl activist Greta Thurnburg has also given a speech to activists in Rome, Italy.