SAN FRANCISCO • Mayors, governors, entrepreneurs, chief executives, investors and celebrities delivered a double-edged message last Friday at the close of a climate summit in San Francisco: Global warming is making the planet unliveable - but we know how to fix it.
"We are using the sky as an open sewer; it's insane," former United States vice-president Al Gore told the conference, noting that humanity belches 110 million tonnes of heat-trapping pollution into the atmosphere every day.
"Will we change? That's what the Global Climate Action Summit is all about."
Over three days, thousands of delegates from the private and public sectors showcased policies and innovations aimed at reducing that flow of greenhouse gases.
Cities are converting to all-electric vehicle fleets and setting deadlines for banishing gas-guzzling cars from their roads; companies have vowed to operate only with renewable energy, including a few smokestack multinationals in the developing world.
"Clean and green is profitable," said Mr Mahendra Singhi, CEO of Dalmia Cement in India.
Investors managing fortunes said they were purging coal, oil and gas from their portfolios; young entrepreneurs showed off energy-efficiency apps and inventions.
Provincial and state governors in tropical countries vowed to empower indigenous peoples who have been managing forests sustainably before "sustainable" was even a word.
But all these efforts may be in vain, the delegates warned, if national governments fail to do their part.
"Now is the time for all leaders to step up and take bold action," they said in an appeal framed as a Call to Action. "We call on the national governments of the world to step up ambition now... and chart a clear path to your zero-carbon future."
Mr Paul Polman, CEO of Unilever, one of the world's largest consumer goods companies, said: "We have enough critical mass in the private sector now to help spur that political process."
The 196-nation Paris Agreement, inked in 2015, enjoins nations to cap global warming this century at "well below" 2 deg C, and to strive for a ceiling of 1.5 deg C if possible.
With only 1 deg C of warming so far, earth has seen a rise in deadly heatwaves, droughts, floods and superstorms engorged by rising seas.
But United Nations talks to implement the treaty, which goes into effect in 2020, have stalled over disagreements on money to help poor countries green their economies and brace themselves for unavoidable climate impacts.
More urgent still is the so-called "ambition gap" between voluntary national commitments to curb carbon pollution, and what is needed to keep global temperature rises under 2 deg C.
Even if all nations honour current pledges - many of which depend on climate finance that does not yet exist - the world will heat up by an unbearable 3.5 deg C, scientists have calculated.
A climate summit convened by UN Secretary-General Antonio Guterres next fall "is what is going to determine whether we can save the Paris Agreement or not", said Mr David Paul, Environment Minister for the Marshall Islands.
The transition to a greener global economy has been hampered by US President Donald Trump, who opted out of the Paris pact months after taking office, saying it would pose a "burden" on the US economy.
Mr Trump has also taken a sledgehammer to the climate policies of his predecessor, Mr Barack Obama, relaxing pollution rules for coal-fired power plants and rolling back car-mileage standards.
But the American people are "way smarter", said former US secretary of state John Kerry, pointing to the conference and climate change policies in dozens of states across the country.