A trio of central European countries have blocked the EU from inching closer to a net-zero carbon emissions target for 2050.

European leaders meeting in Brussels sparred over the EU’s role in tackling the unfolding climate emergency, which threatens to significantly worsen the risks of drought, floods, extreme heat, poverty and destruction of wildlife around the world.

Dashing earlier hopes of a compromise, Poland and the Czech Republic refused to sign up to a text that referred to a climate-neutral EU by 2050 – a target that was already seen as too vague by green activists.

In a further blow, the Hungarian prime minister, Viktor Orbán, joined his neighbours in opposing the EU text, despite earlier signs the country was ready to compromise.

Supporters of the 2050 plan hoped the EU could show it was moving in that direction ahead of a major UN climate summit in September. Instead the 2050 date was dropped into a footnote that stated: “For a large majority of member states, climate neutrality must be achieved by 2050.”

The German chancellor, Angela Merkel, told her fellow leaders that the EU needed to signal ambition ahead of that meeting. The French president, Emmanuel Macron, called for the EU to agree an unambiguous target for net-zero carbon emissions by 2050.

But the Central European trio stood their ground against any mention of 2050 in the main EU summit communiqué.

The Czech prime minister, Andrej Babiš, had quipped on his arrival at the summit: “Why should we decide 31 years ahead of time what will happen in 2050?”

Inside the meeting, Babiš questioned why Europe should act when emissions in China were rising, prompting a retort from the German chancellor. She countered that the Chinese were taking action that would mean a reduction in Chinese emissions after 2030.

While supporters of the 2050 plan were disappointed, they are not giving up. “It’s not a matter of if the EU commits to climate neutrality, it’s when,” one diplomat said.

A large majority of EU member states support the aim of net zero carbon emissions by 2050.

Hopes had grown in recent days, after Slovakia, Bulgaria and some Baltic states announced their support for the 2050 target, seeing economic gains from the transition to a green economy. “We have come to the conclusion that this is a hell of an opportunity,” the Latvian prime minister, Krišjānis Kariņš, told his fellow leaders.

Earlier a senior EU diplomat said the debate among member states had moved on significantly since earlier discussions in March, when countries were “very divided”. They said: “We still do not have unanimity, but an overwhelming majority of member states, including member states you would never expect of being ready to accept such an objective are going in that direction.”

The UN secretary general, António Guterres, wants the climate summit in September to put the world on a path to limiting global warming to 1.5C – a non-binding aspiration of the 2015 Paris accord.

Guterres wrote to European council president, Donald Tusk, last month and called on him to demonstrate the leadership of the EU. “I write to you today both as a G20 member and as a leader who I believe can bring the ingenuity needed to transform our economic systems and avert the negative impacts of a world with high levels of carbon emissions – from rising levels of pollution to costly natural disasters,” he stated.

The letter calls for a change of course to “achieve net zero carbon emissions by 2050” and specifies that leaders should curtail current coal-burning power stations and discontinue new ones beyond 2020.

Responding to the EU’s failure to agree a 2050 target, green campaigners called on the EU to hold an emergency climate summit ahead of the UN meeting in September.

“Hollow words can’t rebuild a house flattened in a mudslide or repay a farmer who’s lost their harvest to drought, said Greenpeace EU climate policy advisor Sebastian Mang. “Merkel and Macron failed to convince Poland and bring others on board. With people on the streets demanding action and warnings from scientists that the window to respond is closing fast, our governments had a chance to lead from the front and put Europe on a rapid path to full decarbonisation. They blew it.”

