The world faces imminent disaster without urgent action on climate change, with the damage we can already see becoming unstoppable, the United Nations secretary-general told leaders gathered for a major climate conference in Glasgow, Scotland.

"Our addiction to fossil fuels is pushing humanity to the brink," António Guterres said in opening remarks to the 26th meeting of the Conference of Parties, known as COP26, on Monday. "We face a stark choice: Either we stop it — or it stops us."

"We are digging our own graves," he warned.

Guterres is pushing the world's nations to commit to more ambitious climate action – with a 45% cut in carbon dioxide emissions by 2030 and net carbon emissions by 2050. These are goals that scientists say must be reached if the global community has any chance of holding warming to 1.5 degrees Celsius this century.

But the COP26 conference opened a day after the G-20 economies noted only vaguely "the key relevance" of halting net emissions "by or around mid-century" without setting a timetable even for phasing out coal.

"Our planet is changing before our eyes — from the ocean depths to mountain tops; from melting glaciers to relentless extreme weather events," the secretary-general said.

He warned that a rise in sea levels was set to double in 30 years, that oceans "are hotter than ever — and getting warmer faster," and that the Amazon rainforest is now a net emitter of carbon — contributing to the problem instead of helping to ameliorate it.

In the face of all that, he said, recent efforts to address the problem have been mostly "an illusion."

"We are still careening towards climate catastrophe," Guterres said, and if serious action isn't taken, "temperatures will rise well above 2 degrees."

He said the world must recommit itself to the 1.5 degree goal, and "if commitments fall short by the end of this COP, countries must revisit their national climate plans and policies. Not every five years. Every year."

Without sustained effort, "We are fast approaching tipping points that will trigger escalating feedback loops of global heating," he said. But investment in climate-resilient economies aimed at net-zero emissions will "create feedback loops of its own — virtuous circles of sustainable growth, jobs and opportunity."

This story originally appeared on the Morning Edition live blog.