More than 200 scientists told the COP26 summit Thursday to take immediate action to halt global warming, warning in an open letter that some climate change impacts were “irreversible” for generations. The central task of the Glasgow meeting is to implement the Paris Agreement, with its goal of limiting temperature rise to between 1.5 and 2 degrees Celsius above pre-industrial levels. But as negotiations enter their final days, commitments made so far could still lead to “catastrophic” warming of as much as 2.7C by 2100, according to the UN. “We, climate scientists, stress that immediate, strong, rapid, sustained and large-scale actions are necessary,” to keep warming within the Paris target, said the letter, signed by researchers across the world. In August, a bombshell “code red” report from the world’s top climate science body, the Intergovernmental Panel on Climate Change (IPCC), warned that Earth’s average temperature will hit the 1.5C threshold around 2030, a decade earlier than projected only three years ago. To keep from overshooting that temperature target the IPCC says emissions must fall 45 percent this decade. Thursday’s open letter, signed by some of the IPCC’s report authors, calls on delegates in Glasgow to “fully acknowledge” the scientific evidence they have compiled of the severe threats posed by climate change. “COP26 is a historic moment for the fate of climate, societies and ecosystems, because human activities have already warmed the planet by around 1.1C and future greenhouse gas emissions will determine future additional warming,” the letters said. The heating atmosphere is already magnifying weather extremes, subjecting communities across the world to more intense fire and drought, displacement and severe economic hardship. And emissions are still rising. A major recent assessment showed global CO2 emissions are set to rebound in 2021 to pre-pandemic levels. “Cumulative greenhouse gas emissions to date already commit our planet to key changes of the climate system affecting human society and marine and terrestrial ecosystems, some of which are irreversible for generations to come,” said the letter.