The conference, already delayed by a year owing to the coronavirus pandemic, follows the landmark Paris Agreement in 2015. That global treaty set out measures to limit global emissions to “well below” two degrees Celsius, and preferably 1.5 degrees.

Under that agreement, the signatories must meet every five years—six, in this case—to announce increasingly ambitious climate targets and lay out how they will meet them. This conference will set new commitments, and is expected to address how rich, developed countries will support poorer, developing ones with climate funding, including funding for lower-income countries. Developed countries have already agreed to give $100 billion to developing countries to help them adapt to climate change—a promise that remains unfulfilled.

As a reminder of the stakes of COP26, the UN, its own Intergovernmental Panel on Climate Change (IPCC), and climate scientists have repeatedly warned that despite momentum behind the growth of renewable energy and government commitments, slow and insufficient action has kept the world on track for dangerous levels of climate change. In August, the latest IPCC report issued a “code red” for humanity, equivalent to the world’s scientists “screaming at the top of their lungs on top of the tallest building” that the window for limiting temperature rise was narrowing, as climate scientist Michael E. Mann put it.

Patricia Espinosa, executive secretary of the UN’s Framework Convention on Climate Change, quoted the Scottish poet Robert Burns in prepared remarks on Sunday. “Now is the day, now is the hour,” she said, marking the official opening of the conference.

“We stand at a pivotal point in history. Humanity faces several stark but clear choices,” her comments read. “We either choose to achieve rapid and large-scale reductions of emissions to keep the goal of limiting global warming to 1.5°C—or we accept that humanity faces a bleak future on this planet.”

On Monday, world leaders are scheduled to deliver statements outlining their countries’ individual commitments for reducing emissions. Although the final announcement of a global agreement between the delegates will only come at the end of the two-week conference, speeches by the likes of U.K. Prime Minister Boris Johnson and U.S. President Joe Biden will offer a crucial chance for national governments to announce fresh climate targets and gain a sense of the global sentiment going into the event.

The appearances come a day after many of the same world leaders met in Rome for a climate-themed G20 summit, which produced an agreement by 20 top economies to not fund coal projects outside their own countries, and demonstrated some consensus around the 1.5 degree target. But the meeting also didn’t produce quite the robust momentum on climate action some were hoping for. UN Secretary-General António Guterres said the meeting left his “hopes unfulfilled—but at least they were not buried.”

The opening of COP26 hasn’t been without initial hiccups, however. British and Western European delegates were encouraged to take the train—rather than fly—to Glasgow, about five hours north of London. Because the rail lines are electrified, the trip has a minimal carbon intensity compared with a short-haul flight.

But an unusually strong storm overnight in the U.K. left rail lines strewn with tree branches on Sunday and damaged electrical rail lines. That resulted in long delays and scores of train cancellations on lines going north to Scotland, and, as some journalists reported, a rush by delegates to secure short-haul flights.

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