Greta Thunberg has challenged political leaders and the media to listen to the science as she warned time was running out to tackle global heating.

Speaking on a panel of young environmentalists in Davos, Thunberg said the increase in global temperature could not be kept below 1.5C if the world continued to use up its limited carbon budget at its current rate.

Davos 2020: Greta Thunberg demands urgent action on climate emergency – day one live Read more

“With today’s emissions levels, the remaining budget is gone in less than eight years. These aren’t anyone’s views, this is the science,” Thunberg said, citing a 2018 Intergovernmental Panel on Climate Change (IPCC) report. “I know you don’t want to report this or talk about this but I will keep repeating the numbers until you do.”

The 2018 IPCC report said that the world had a limit of 420 gigatons of carbon to emit if there was to be a 67% chance of keeping the increase in global temperatures to 1.5 degrees. Thunberg said that was now down to 340 gigatons.

There was an assumption, she said, that “future generations will somehow suck hundreds of billions of tonnes of CO2 out of the atmosphere, even though such technology doesn’t exist yet”.

Quick guide What is Davos 2020? Show Hide Davos is a Swiss ski resort now more famous for hosting the annual four-day conference for the World Economic Forum. For participants it is a festival of networking. Getting an invitation is a sign you have made it – and the elaborate system of badges reveals your place in the Davos hierarchy. The meeting is sponsored by a huge number of international banks and corporations.

For critics, “Davos man” is shorthand for the globe-trotting elite, disconnected from their home countries after spending too much time in the club-class lounge. Others just wonder if it is all a big waste of time. The 2020 meeting is being advertised as focusing on seven themes: Fairer economies, better business, healthy futures, future of work, tech for good, beyond geopolitics and how to save the planet. Young climate activists and school strikers from around the world will be present at the event to put pressure on world leaders over that last theme.

The IPCC forecasts did not include feedback loops or possible tipping points that might make the need for action even more urgent, the Swedish activist said; rich countries needed to get their emissions down rapidly and then help poor countries to make the necessary changes.

“Even with a 1C increase people are dying of climate change. Every fraction of a degree matters.”

Play Video 15:08 Inside the mission to create an army of Greta Thunbergs – video

Thunberg was speaking hours before Donald Trump – a global heating sceptic – was due to make a keynote address to the World Economic Forum.

She said people were more aware of the problem, thanks to the efforts of young people: “It feels like the climate and environment is a hot topic now. But from another perspective virtually nothing has been done. Without treating this as a real crisis we cannot solve it.”

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After a year in which her first appearance at Davos catapulted her to international fame, Thunberg said she could not complain about her voice being heard. “I’m being heard all the time. But the science and the voice of young people are not at the centre of the conversation and they need to be. This is about us and future generations.”