Barack Obama has called on young people to "stay angry" in the fight against climate change at the COP26 summit.
The former US president urged them to apply political pressure to make a change, but warned they would need to accept compromises along the way.
Mr Obama said the world is "nowhere near where we need to be" to avoid a future climate catastrophe.
He criticised Donald Trump's "active hostility toward climate science", but said the US is ready to lead again.
Mr Obama also scolded China and Russia's leaders for not physically attending the COP26 summit.
Speaking in Glasgow, Mr Obama received rapturous applause when he took to the stage and a standing ovation at the end of his speech - but there was pushback from activists.
He called out nations for failing to meet the pledges they made in the 2015 Paris Agreement, when he was in the White House.
However, activists were quick to point out those broken by his own administration, including the failure of a key promise by developed countries to deliver $100bn (£73bn) a year in climate finance to poorer nations.