Donald's not taking Greta's naming as Time's Person of the Year well.
The 16-year-old turned the US President's latest attack into her Twitter bio.
"Little Miss 'How Dare You' has clearly had a lot of exposure this year."
Scientists say it's speeding up much faster than expected.
One prominent critic of the teen climate activist offered his congratulations.
The teenage Swedish climate activist called it an "unbelievable" honour.
"The manufacture of Christmas cards is contributing to our ever-growing carbon emissions."
They sang protest songs and had slogans such as "act now" and written on their chests and stomachs.
A global agreement in the 1980s to cut CFCs and save the ozone layer has had an unexpected spinoff benefit.