The former US president called the 16-year-old Swedish activist "one of our planet's greatest advocates."
Former US president Barack Obama has met with 16-year-old climate activist Greta Thunberg as part of her visit to Washington DC to lobby lawmakers on environmental issues.
On Twitter, Obama called the Swedish teenager “one of our planet’s greatest advocates” who is “unafraid to push for real action”.
“All these young people seem so eager, very enthusiastic, which is a very good thing,” Greta told Mr Obama during the meeting.
“No one is too small to make an impact and change the world so just do everything you can. Be creative.”
Greta arrived in the US last month from the UK after a two-week voyage across the Atlantic Ocean on a zero-emissions yacht.
This Friday the 16-year-old and thousands of New York students are expected to pour into the streets as part of a “global climate strike” along with other protests around the world.
It is not known how many people will attend but celebrities and non-governmental organizations have called for large numbers of people to take to the streets.
New York authorities have given their blessings to the one million children in over 1,700 schools in the US financial capital to miss school for the event.
Hundreds of thousands of youths in at least 150 countries have said they will walk out of school in solidarity with her.
That will be followed on Saturday by the first Youth Climate Summit at the UN and the Climate Action Summit on Monday, which the UN chief has convened because the world's biggest polluters remain woefully behind their greenhouse gas emissions targets.
Amnesty 'Ambassadors of Conscience' Award
The Swedish environmental activist received Amnesty International’s “Ambassadors of Conscience” award on Monday for their work highlighting the need for urgent action to avert climate disaster.
The teenager, who is taking a year out of high school, received a standing ovation from students at The George Washington University in the US capital where the ceremony was held.
"The politics required to take on this crisis simply doesn't exist today," Thunberg said, standing on a step to reach the microphone.
"That is why every single one of us must push from every possible angle to hold those responsible accountable and to make the people in power act."
She added that the prize was not just for her but the millions of youth who have taken part since last year in weekly school strikes held every Friday, inspired by the sit-in she began outside Sweden's parliament in August 2018.