The UN secretary-general has warned that the world is facing "a direct existential threat" and must rapidly shift from dependence on fossil fuels by 2020 to prevent "runaway climate change".
Antonio Guterres called the crisis urgent and criticised the lack of global leadership to address global warming.
"Climate change is moving faster than we are," Guterres said. "We need to put the brake on deadly greenhouse gas emissions and drive climate action."
He said people everywhere are experiencing record-breaking temperatures, and extreme heatwaves, wildfires, storms and floods "are leaving a trail of death and devastation".
He pointed the almost 3,000 deaths from Hurricane Maria in Puerto Rico last year, disappearing Arctic sea ice, oceans becoming more acidic threatening food chains, and high carbon dioxide levels in the atmosphere threatening food security for billions of people.
Guterres said scientists have been warning about global warming for decades, but "far too many leaders have refused to listen - far too few have acted with the vision the science demands".
When 190 nations signed the 2015 Paris agreement on climate change they agreed to limit the global temperature increase by 2100 to less than 2C and as close as possible to 1.5C.
"These targets were the bare minimum to avoid the worst impacts of climate change," Guterres said. "But scientists tell us that we are far off track."
"According to a UN study, the commitments made so far by parties to the Paris agreement represent just one-third of what is needed.
"We need to rapidly shift away from our dependence on fossil fuels. We need to replace them with clean energy from water, wind and sun. We must halt deforestation, restore degraded forests and change the way we farm."
He appealed for leadership - "from politicians and leaders, from business and scientists, and from the public everywhere" - to break what he called the current "paralysis".
"If we do not change course by 2020, we risk missing the point where we can avoid runaway climate change, with disastrous consequences for people and all the natural systems that sustain us," he warned.
The alternative to moving to green energy, he said, "is a dark and dangerous future".
Australian Associated Press