Groups at the protest included #FridaysForFuture, an environmental protest movement started by activist Greta Thunberg. She sat outside the Swedish Parliament every day demanding the government take action on climate change. Her example soon sparked international school strikes. Other key groups in attendance were Greenpeace, cyclist-safety visibility group Critical Mass and Extinction Rebellion.

Critical Mass is a cyclists' environmental protest bicycle ride. It started in 1992 in San Francisco, and now Critical Mass groups are found all over the world. They organize rides in large groups that often block roads to make car drivers aware of cyclists. The Critical Mass website speaks of a "cycling culture that refuses to take a back seat to motorists."

Greenpeace is a non-violent environmental activist group. The organization has set out a plan for the world to be on track by 2020 to keep global climate change below 1.5° C. Among other aims, the group hopes to tackle environmental degradation of forests and oceans.

Evidence has towards the combustion engine's contribution to increasing global temperatures. The German Aerospace Center (DLR) study on car transport, commissioned by Greenpeace Belgium, concluded that to achieve a 66% likelihood of keeping global warming below 1.5°C, diesel and petrol cars must be rapidly phased out in Europe with an end to new sales by 2025.

Air pollution is another target for environmental activists. Air pollution has reached dangerous levels in many cities across the world and there is mounting research on the damage it inflicts on humans and fetuses.

According to the Greenpeace "Crashing the Climate" report into the effect of the car industry on the environment, SUVs are particularly damaging to the environment. Due to their higher weight and less aerodynamic body, SUVs produce significantly higher CO2 emissions than other cars.

Many protesters and environment groups think that governments have been too slow to enact meaningful change to ensure the Earth's temperature doesn't rise above the 2°C benchmark set by climate scientists.

Beginning April 15, protesters with Extinction Rebellion took to the streets of London and other cities to demand governments declare a climate and ecological emergency. They occupied key spots in the city, calling on those in charge to reduce greenhouse gas emissions to zero by 2025, halt biodiversity loss and set up citizens' assemblies on climate and ecological justice.

Extinction Rebellion, founded last year by academics in the United Kingdom, is one of the world's fastest-growing environmental movements. Their aim is to protest climate change inaction in a creative and nonviolent way. Demonstrators say people are causing their own mass extinction, which is the basis of their "rebellion."

Harry and Meghan, the duke and duchess of Sussex, didn't exactly take part in the sit-in on London's Waterloo Bridge on April 18. The royals are expecting and protesters used the happy event in their demonstration, having the couple "thank" Extinction Rebellion for saving their child's future.

Activists have used a variety of unusual protest methods to draw maximum attention and get their point across. Throughout the week, they've blocked traffic, climbed atop buses and superglued themselves to buildings and, in the case of this young man at London's Canary Wharf station on April 17, trains.

The goal of the protests is to temporarily disrupt everyday life. As a result, police have arrested more than 800 people in London alone. Activists want to get the public on their side, but a YouGov survey showed that just 36% of more than 3,500 British polled support the protest, with 52% against.

Extinction Rebellion protesters first attracted global attention on April 1, during yet another heated Brexit debate in the British Parliament. A group of semi-naked activists revealed themselves in the visitor gallery with slogans including "SOS" and "Stop Wasting Time" written on their bodies, with some gluing their hands to a glass barrier. The scene was quickly broken up my security.

The Extinction Rebellion protests got their start in London, but the movement has also spread to other major cities around the world. On April 15, these activists on the Oberbaum Bridge in Berlin blocked traffic for hours.

On April 21, organizers in London said they were willing to switch tactics and talk with the government. "We're giving them an opportunity now to come and speak to us," said spokesman James Fox. "If they refuse … then this is going to continue and this going to escalate in different, diverse and very creative ways."