The level of carbon dioxide in the atmosphere has hit a record high, according to the UN 

The amount of carbon dioxide in the atmosphere hit a new record last year with emissions showing no sign of slowing down, the U.N. World Meteorological Organization said on Thursday.

The annual Greenhouse Gas Bulletin dashed hopes for a slowdown in emissions of CO2 - the byproduct of burning fossil fuels that scientists say is the main cause of the greenhouse effect causing global warming.

"The science is clear. Without rapid cuts in CO2 and other greenhouse gases, climate change will have increasingly destructive and irreversible impacts on life on Earth. The window of opportunity for action is almost closed," WMO Secretary-General Petteri Taalas said in a statement.

The report found CO2 levels of 405.5 parts per million in 2017, up from 403.3 ppm in 2016.

The rate of increase is in line with the average growth rate over the last decade, which was the fastest rate for 55 million years, the WMO said. Carbon dioxide levels have risen 46 percent since the pre-industrial era, around 1750.

"The most alarming thing is that ... half of the increase from pre-industrial times comes within the last 30 years," said Oksana Tarasova, head of WMO's atmospheric environment research.

The rise was expected to be much lower in 2017, because the previous year saw "El Nino" weather conditions, which are normally followed by a big slowdown in the growth of CO2 concentrations.

U.N. climate talks in Poland next month are meant to agree a rule book for the 2015 Paris agreement on climate change, which set a sweeping goal of ending the fossil fuel era this century.

U.N. human rights chief Michelle Bachelet has sent a letter to all states, telling them they have legal obligations under international human rights law to prevent climate change and try to mitigate its effects.

The United States is the only country to have announced its intention to withdraw from the Paris accord, and President Donald Trump has cast doubt on the science underpinning it.

"Brutal and Extended Cold Blast could shatter ALL RECORDS - Whatever happened to Global Warming?", Trump tweeted on Wednesday.

WMO chief scientist Pavel Kabat said unusually cold weather was consistent with climate change.

"On the longer timescale we are not that much worried about the current political disturbance," he said.

"Global warming is unequivocal," added WMO Deputy Secretary-General Elena Manaenkova. "Climate change is scientifically proven."