Hike in carbon emissions puts world on track for catastrophic global warming
Greenhouse gas emissions from power generation, transport, agriculture and industry have risen for the first time in four years.
The UN says emissions rose in 2017 after stabilising between 2014 and 2016, with no signs of them peaking in the short-term.
This means the world is on course of a 3.2C rise in average global temperatures by the end of the century - well in excess of the 1.5C 'safe' limit.
The Emissions Gap report from UN Environment says it is still possible to keep global warming below 2C, but that the likelihood of keeping it to 1.5C is "dwindling".
It presents an annual assessment of the so-called 'emissions gap' - the difference between expected emission levels in 2030 compared with the levels needed to keep hikes to no more than 2C - and finds that countries need to ramp-up ambition to avoid catastrophic climate change.
National commitments are not enough, it finds. This is because just 57 countries, which represent 60pc of global emissions, are on track to meet commitments by 2030. It also highlights nations must raise their ambition three-fold to keep global warming to no more than 2C, and five-fold to keep rises to 1.5C.
"The science is clear," UN Environment deputy executive director Joyce Msuya said. "For all the ambitious climate action we've seen, governments need to move faster and with greater urgency. We're feeding this fire while the means to extinguish it are within reach."
Many of the measures needed to reduce emissions are already available, but deployment needs to be scaled-up, it adds.
These include mass deployment of electric vehicles and renewable energy, phasing out of coal-fired power stations and improving building energy efficiency.
To keep warming below 2C, "drastic, large-scale action" is "urgently" needed, including use of carbon taxes to incentivise behaviour change.
Revenues could be used to reduce other taxes or help low-income families adjust, it adds.