World leaders have reaffirmed their commitment to cutting greenhouse gas emissions, after Theresa May urged them to do more on climate change.
The prime minister called on the G20 countries to set targets for net zero greenhouse gas emissions.
Instead, 19 pledged to meet their targets set in the 2015 Paris agreement. The US did not sign up.
The UK is the first country to enshrine in law a commitment to be a net zero emitter of CO2 by 2050.
Mrs May called on other world leaders to follow suit, aiming for the summit’s joint statement to have “the strongest wording we can deliver” on climate change.
But only 19 of the 20 leaders signed up to the statement, which committed them to the “irreversibility” of the 2015 Paris agreement and pledged the full implementation of its targets to reduce greenhouse gas emissions.
US President Donald Trump declined to sign.
“In recent months we have heard hundreds of thousands of young people urge us – their leaders – to act on climate change before it’s too late,” Mrs May said.
She said the UK’s net zero goal was “world-leading” and she called on other countries to “raise their ambition and embrace this target”.
The UK’s target means it will have to eliminate greenhouse gas emissions completely or – in the most difficult cases – offset them by planting trees or absorbing CO2 from the atmosphere.
Under the Paris agreement, reaffirmed by the 19 world leaders, every nation is committed to keeping global temperature rises to less than 2C (3.6F) higher than pre-industrial times.
Scientists say that a 1.5C rise is the threshold for dangerous climate change, and if other countries adopted the UK’s net zero target, there was a 50-50 chance of staying below this by 2100.
Separately, in a 20-minute meeting with Saudi crown prince Mohammed Bin Salman, she raised the case of murdered journalist Jamal Khashoggi, a British official said.
US intelligence concluded the crown prince directed the killing of the Washington Post columnist at the Saudi consulate in Turkey last year, but Saudi authorities have denied they were acting on his orders.
With 11 unidentified people put on trial behind closed doors, Mrs May told Prince Mohammed that the legal process must be “open and transparent”, the official said.
Mrs May also called for other countries to follow the UK’s pledge of £1.4bn to the Global Fund, an international organisation which fights three of the world’s deadliest diseases.
The UK will contribute £467m a year for three years, providing tuberculosis treatment for more than two million people, 90 million mosquito nets to protect people from malaria, and treatment for more than three million people living with HIV – the virus which causes Aids.
Mrs May said the world needed “urgent international action and a truly collective response” to halt the spread of these illnesses.
The pledge follows an appeal by Sir Elton John and French President Emmanuel Macron for an £11bn cash injection for the Global Fund, which is expected to help save 16 million lives.
Sir Elton, whose Aids foundation works with the fund, said the UK’s response set an “extraordinary example for others to follow”.