The movement, also known as XR, now has chapters in some 50 countries.
The group has scheduled non-violent protests chiefly in Europe, North America and Australia over the next two weeks. Events will also be held in India, Argentina, and South Africa.
An "opening ceremony" on Sunday evening attracted hundreds of people to central London, where plans are in place to shut down key sites - including Westminster and Lambeth bridges - in addition to protests outside key government departments.
Hundreds of activists barricaded themselves inside a Paris shopping centre for hours over the weekend, unfurling banners with slogans such as "Burn capitalism, not petrol" above restaurants and fashion boutiques.
In New Delhi, one of the world's most polluted cities, dozens of protesters staged another preliminary event by holding a "die-in" on a road in the heart of India's capital.
Holding up hands covered in red paint and signs such as "There is no planet B", they called on the Indian government to act to tackle climate change.
"I don't know if I will have a future or not," Vansha Jain, 17, told AFP news agency. [mr/aje]