UN Secretary General Antonio Guterres has called on the G20, nations responsible for 80 per cent of greenhouse gas emissions, to intensify their climate response amid “flat-lining” action.
Mr Guterres made an urgent appeal to world leaders to act now and "lower the temperature" so as not to "drown" the world.
Before the 77th UN General Assembly, he said the international community must do more to help countries that are hit hardest by the effects of climate change.
“If one third of G20 countries was under water today, as it could be tomorrow, perhaps they would find it easier to agree on drastic cuts to emissions," Mr Guterres said after his recent visit to flood-ravaged Pakistan.
He said he had "never seen climate carnage" on such a scale, blaming wealthier countries for the devastation.
"What is happening in Pakistan demonstrates the sheer inadequacy of the global response to the climate crisis, and the betrayal and injustice at the heart of it," Mr Guterres said.
Almost 1,400 people have died as a result of flooding in Pakistan, with water destroying crops, homes, businesses and much of the infrastructure.
“Unless action is taken now, unless funds are disbursed now, these tragedies will simply multiply, with devastating consequences for years to come including instability and mass migration around the world,” Mr Guterres said.
His comments were also directed at major fossil fuel companies, which he accused of "killing the planet to rake in the most".
“Whether it’s Pakistan, the Horn of Africa, the Sahel, small islands, or least developed countries, the world’s most vulnerable – who did nothing to cause this crisis – are paying a horrific price for decades of intransigence by big emitters,” Mr Guterres said.
He also warned of a "real risk of food shortages next year" and the prospect of a “fertiliser market crunch".
The UN chief spoke with President Vladimir Putin on Wednesday morning, to try to broker a deal to increase the amount of Russian food and fertiliser exported through the Black Sea.
"Obstacles must be removed to Russian food and fertiliser exports, that are not subject to sanctions," Mr Guterres said.
"We are looking not only at maintaining the grain deal, but expanding it.
"We had the opportunity to discuss the Black Sea Green Initiative and its extension and possible expansion … and the possibility of ammonia exports through the Russian Federation.”
He said the prospects of a peace deal between Russia and Ukraine were "still far away".
"My speech to the General Assembly will address these issues with concrete recommendations and a call to action," Mr Guterres said.
"As fractures deepen and trust evaporates, we need to come together around solutions."