The United Nations’ two-week-long climate negotiations in Madrid, Spain, ended Sunday with major polluters resisting calls to ramp up efforts to slow global warming.

Negotiators approved a call for greater efforts to tackle climate change and several measures to help poor countries respond and adapt to its impacts.

U.N. Secretary-General António Guterres said the conference results “disappointed” him. He said it was a lost opportunity to be more aggressive in dealing with climate change.

“We must not give up, and I will not give up,” he said.

The final declaration cited an “urgent need” to cut planet-heating greenhouse gases in line with the goals of the 2015 Paris climate-change accord. But it fell far short of demanding that countries submit bolder emissions proposals next year, which developing countries and environmentalists had demanded.

The Paris accord established a common goal of keeping temperature increases below 2 degrees Celsius (3.6 Fahrenheit), ideally 1.5 degrees Celsius (2.7 degrees Fahrenheit) by the end of the century. So far, the world is on course for a 3- to 4-degree Celsius rise, with potentially dramatic consequences for many countries, including rising sea levels and fiercer storms.

Delegates deferred some of the toughest issues to the November climate summit in Glasgow, Scotland.

Chile’s Environment Minister Carolina Schmidt, who led the meeting, said she was “sad” no deal had been reached on the rules for international trading in carbon emissions permits.

Economists say putting a price on carbon dioxide, the main greenhouse gas, and letting countries or companies trade emissions permits, will help the world shift away from fossil fuels toward renewable energy.

The talks in Spain took place against a backdrop of growing worldwide concern about climate change. The past year saw large protests in hundreds of cities around the globe and climate activists staged several rallies inside and outside the conference venue to express their frustration at the slow pace of the talks.

Under the Paris accord, countries are supposed to regularly review their national emissions reduction targets and increase them if necessary. Last week, the European Union agreed a goal of becoming carbon neutral by mid-century, but the move did little to sway discussions in Madrid about setting more ambitious targets in the medium term, an issue that will be on the agenda again in Glasgow.

The United States will be excluded from much of those talks after President Trump announced the country’s withdrawal from the Paris accord, a process than comes into force November 4, 2020.

Scientists said the longer countries wait to cut emissions, the harder it will be to meet the Paris temperature target.

“The global emissions’ curve needs to bend in 2020,” said Johan Rockstrom, director of the Potsdam Institute for Climate Impact Research near Berlin, Germany.

“Emissions need to be cut half by 2030, and net zero emissions need to be a reality by 2050,” he said. “Achieving this is possible — with existing technologies and within our current economy. The window of opportunity is open, but barely.”