The EU and scores of developing countries have pledged to toughen their existing commitments to reduce greenhouse gas emissions to enable the world to stay within a 1.5C rise in global warming.

The promise, which follows increasingly dire scientific warnings, was the most positive message yet to come from the ongoing talks in Poland.

The announcement came at the end of a day in which the UN secretary general made an impassioned intervention to rescue the talks, which have been distracted by US, Russian and Saudi moves to downgrade scientific advice.

“We’re running out of time,” António Guterres told the plenary. “To waste this opportunity would compromise our last best chance to stop runaway climate change. It would not only be immoral, it would be suicidal.”

The talks have centred on devising a rulebook for implementing the 2015 Paris agreement and raising countries’ level of ambition to counter climate change, but progress has been slow on several key issues and divisions have emerged between four fossil fuel powers – the US, Russia, Saudi Arabia and Kuwait – and the rest of the world.

The UN believes China could play a stronger role in the absence of leadership from the US. Sources said Guterres would make a telephone call to Xi to ask for his help in nudging talks forward.

The EU also wants China, which is a key member of the block of 77 developing countries, to step up to ensure that countries all follow the same rules in being transparent over their greenhouse gas emissions.

Campaigners praised the decision by the High Ambition Coalition group of countries, made up of the EU and four other developed countries, including Canada and New Zealand, as well as the large grouping of least developed countries and several other developing nations, to scale up their emissions-cutting efforts in line with a 1.5C temperature rise limit.