Sharp and potentially devastating temperature rises of 3C to 5C in the Arctic are now inevitable even if the world succeeds in cutting greenhouse gas emissions in line with the Paris agreement, research has found.

Winter temperatures at the north pole are likely to rise by at least 3C above pre-industrial levels by mid-century, and there could be further rises to between 5C and 9C above the recent average for the region, according to the UN.

Such changes would result in rapidly melting ice and permafrost, leading to sea level rises and potentially to even more destructive levels of warming. Scientists fear Arctic heating could trigger a climate “tipping point” as melting permafrost releases the powerful greenhouse gas methane into the atmosphere, which in turn could create a runaway warming effect.

Joyce Msuya is the acting executive director of UN Environment. Photograph: Simon Maina/AFP/Getty Images

“What happens in the Arctic does not stay in the Arctic,” said Joyce Msuya, the acting executive director of UN Environment. “We have the science. Now more urgent climate action is needed to steer away from tipping points that could be even worse for our planet than we first thought.”

The findings, presented at the UN Environment assembly in Nairobi on Wednesday, give a stark picture of one of the planet’s most sensitive regions and one that is key to the fate of the world’s climate.

Last year’s stark warnings from the Intergovernmental Panel on Climate Change, setting out the dramatic impacts of 1.5C of global warming, did not include the impacts of potential tipping points such as melting permafrost.

If melting permafrost triggers a tipping point, the likely results would be global temperature rises well in excess of the 2C set as the limit of safety under the Paris agreement. Nearly half of Arctic permafrost could be lost even if global carbon emissions are held within the Paris agreement limits, according to the UN study.

Even if all carbon emissions were to be halted immediately, the Arctic region would still warm by more than 5C by the century’s end, compared with the baseline average from 1986 to 2005, according to the study from UN Environment.

That is because so much carbon has already been poured into the atmosphere. The oceans also have become vast stores of heat, the effect of which is being gradually revealed by changes at the poles and on global weather systems, and will continue to be felt for decades to come.

The assembly heard that there was still a need to fulfil the aims of the 2015 Paris agreement on climate change and to take further action that could stave off some of the worst effects of warming in the near term. “We need to make substantial near-term cuts in greenhouse gas emissions, black carbon and other so-called short-lived climate pollutants all over the world,” said Kimmo Tiilikainen, Finland’s environment minister.

Making drastic cuts to black carbon and short-lived pollutants such as methane could reduce warming by more than 0.5C, according to previous research.