"She's now led millions of people around the world, 150 countries, to act on behalf of the planet, and she's really been a key driver this year taking this issue from backstage to center".
The teenage activist, who began the climate strikes with a solo protest outside the Swedish parliament in August 2018, said: "Every great change in history comes from the people".
She is the youngest individual to have won the accolade.
"Margaret Atwood compared her to Joan of Arc".
"Recently a handful of rich countries pledged to reduce their emission of greenhouse gases by so and so many percent by this or that date, or to become climate neutral or net zero in so and so many years", she said.
Activist Greta Thunberg accused governments and businesses of misleading the public by holding climate talks that are not achieving real action against what she called the world's "climate emergency".
She was typically blunt in her assessment of politicians' efforts.
"Finding holistic solutions is what the COP should be all about, but instead, it seems to have turned into some kind of opportunity for countries to negotiate loopholes and to avoid raising their ambition", she added, to wide applause.
"I'm sure that if people heard what was going on and what was said ... during these meetings, they would be outraged".
Others, however, were less than pleased with the magazine's choice.
Thunberg has become the face of the youth climate movement.
American actor Harrison Ford said it is time to listen to those "who will inherit what we have wrought".
"Flight-shaming" has gained momentum, especially in Europe, where some travelers concerned about the environmental impact of flying are seeking alternative forms of transport.
At little over 1C of warming since the industrial period started, Earth in 2019 was shaken by a string of deadly wildfires, superstorms and floods made more intense by the changing climate.
U.S. House Speaker Nancy Pelosi, the anonymous Central Intelligence Agency official responsible for kickstarting the impeachment proceedings, and the relentless Hong Kong protesters have also been nominated for the title.
"We are still seeing too many bureaucratic and regulatory obstacles, including perverse fossil fuel subsidies and many other expressions of government action slowing down the private sector commitment to climate action".
Time previously featured her on their May cover and called her a "next generation leader".
"This is all wrong". "Tell me how do you react to these numbers without feeling at least some level of panic".
Li Gao, head of the Department of Climate Change under China's Ministry of Ecology and Environment and deputy head of the Chinese delegation to COP25, told Xinhua that financing and support by developed countries to developing ones are always outstanding and crucial issues in climate talks.