The burning of fossil fuels around the world is set to hit a record high in 2017, climate scientists have warned, following three years of flat growth that raised hopes that a peak in global emissions had been reached.

The expected jump in the carbon emissions that drive global warming is a “giant leap backwards for humankind”, according to some scientists. However, other experts said they were not alarmed, saying fluctuations in emissions are to be expected and that big polluters such as China are acting to cut emissions.

Global emissions need to reach their peak by 2020 and then start falling quickly in order to have a realistic chance of keeping global warming below the 2C danger limit, according to leading scientists. Whether the anticipated increase in CO2 emissions in 2017 is just a blip that is followed by a falling trend, or is the start of a worrying upward trend, remains to be seen.

Much will depend on the fast implementation of the global climate deal sealed in Paris in 2015 and this is the focus of the U.N. summit of the world’s countries in Bonn, Germany this week. The nations must make significant progress in turning the aspirations of the Paris deal into reality, as the action pledged to date would see at least 3C of warming and increasing extreme weather impacts around the world.

Global carbon emissions from fossil fuels set to jump by 2% in 2017

Billion of tonnes of carbon dioxide per year

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The 12th annual Global Carbon Budget report published on Monday is produced by 76 of the world’s leading emissions experts from 57 research institutions and estimates that global carbon emissions from fossil fuels will have risen by 2% by the end of 2017, a significant rise.

“Global CO2 emissions appear to be going up strongly once again after a three-year stable period. This is very disappointing,” said Prof Corinne Le QuÃ©rÃ©, director of the Tyndall Centre for Climate Change Research at the UK’s University of East Anglia and who led the new research. “The urgency for reducing emissions means they should really be already decreasing now.”

“There was a big push to sign the Paris agreement on climate change but there is a feeling that not very much has happened since, a bit of slackening,” she said. “What happens after 2017 is very open and depends on how much effort countries are going to make. It is time to take really seriously the implementation of the Paris agreement.” She said the hurricanes and floods seen in 2017 were “a window into the future”.

The new analysis is based on the available energy use data for 2017 and projections for the latter part of the year. It estimates that 37bn tonnes of CO2 will be emitted from burning fossil fuels, the highest total ever.

The main reason for the rise is an expected 3.5% increase in emissions in China, the world’s biggest polluter, where low rains have reduced low-carbon hydroelectric output and industrial activity has increased. India’s rise in emissions was modest compared to previous years at 2%, while the US and EU are both on track for small falls.

2017 is likely to be the hottest year ever recorded in which there was no El NiÃ±o event, a natural global cycle that temporarily nudges up global temperature. The concentration of CO2 in the atmosphere also saw a record jump in 2016, and other greenhouse gases such as methane and nitrous oxide from agriculture and industry are also rising.

“The news that emissions are rising after the three-year hiatus is a giant leap backwards for humankind,” said Amy Luers, executive director of Future Earth, a global research initiative. “Pushing the Earth closer to tipping points is deeply concerning. Emissions need to peak soon and approach zero by 2050.”

However, climate economist Prof Nicholas Stern, at the UK’s London School of Economics, said: “I would not be alarmed. There will be some fluctuations, for example around poor rains and hydro. We should also remember that the methods used to calculate emissions will have their own errors.”

He said there is strong climate action in China: “It has a very clear strategy, particularly on coal and energy efficiency and they are getting, and will get, results.” But Stern said it remains vital that all countries ramp up the ambition of their emissions pledges and that richer countries support action across the world.

Climate scientist Prof Michael Mann, at Penn State University in the US, said the research was authoritative but also urged caution, noting that the 2% projected rise in emissions is small relative to the overall uncertainties in the data. “It seems to me they are over-interpreting the 2017 numbers and jumping the gun a bit. Can’t we wait until the actual numbers are in to do a post-mortem?”

The ability to monitor emissions quickly and accurately is of growing importance. The Paris agreement is based on voluntary cuts by nations, and without verification that pledges have been fulfilled, the trust that underpins the deal could be eroded. “This puts immense pressure on the scientific community to develop methods that can truly verify changes in emissions,” said Le QuÃ©rÃ©.