The protests driven by several mostly youth-led, local and global climate groups and organisations, including Greta Thunberg's Fridays for Future movement were taking place in dozens of countries.
The climate campaigner will be later released, informed the police.
The Tate brothers have been under criminal investigation since April.
The latest victim of Greta's retort is the controversial US media personality and former kickboxer Andrew Tate.
The new species, Pristimantis gretathunbergae, popularly known as Greta Thunberg Rain frog was first discovered in 2012.
Campaigners and pressure groups have been underwhelmed by the commitments made so far, many of which are voluntary, exclude the biggest polluters, or set deadlines decades away.
The complaint was filed with the U.N. Committee on the Rights of the Child in 2019 and the 18-member panel has been conducting hearings and deliberating since.
Thousands of young activists converged on Milan from about 190 countries, due to engage with policymakers to hammer out proposals for possible solutions.
Australian student Izzy Raj-Seppings has abandoned frivolous extracurricular activities in favour of stepping up pressure on the country's leadership to battle climate change.
Global governments appeared to have given up on the goal of limiting global warming to an increase of 1.5 degrees compared to pre-industrial levels, she said.