"And yet. All of this still has not resulted in any political action. Because we still fail to make the connection between the climate crisis and increased extreme weather events and nature disasters like the #AustraliaFires."
Thunberg said made an impassioned call for action.
"That has to change. And it has to change now," she posted.
"My thoughts are with the people of Australia and those affected by these devastating fires."
Australia is on fire. And the summer there has only just begun. 2019 was a year of record heat and record drought. Today...
Posted by Greta Thunberg on Saturday, 4 January 2020
Within hours, her post has attracted thousands of likes, shares and comments.
"Thank you Greta. The situation here is horrendous. The smell and taste of ash is everywhere, the skies are black and blood red, even in the middle of the day, and the screams of dying animals can be heard throughout the bush," one Facebook user wrote,
Another said: "It really says a lot about us as a species when a 16 year old has more intelligence, common sense and compassion than the world leaders. You give me hope for my children Greta, they just take that hope away and my heart breaks seeing this all over the news."
"This must be the tipping point. It must. Everyone, find your humanity and email or call your politicians and scream in their ears to ACT NOW in your country. We're at the gate … now or never. ACT."
She joins a slew of other global figures who have sent messages of support to Australians, including the royal family, actress Bette Midler, pop star Pink and countless others.