United Nations Secretary-General Antonio Guterres said that time is running out to keep global warming low enough to prevent devastating climate change, adding that it is the “defining threat of our time.”

The director of the world body was speaking at the UN climate change body’s annual negotiations (COP23) in Bonn, Germany where countries are hammering out details on how to implement the Paris Agreement.

The accord was signed by nearly 200 countries - most recently previous holdouts Syria and Nicaragua - in an effort to curb global carbon emissions and keep global warming to under 2C.

The agreement goes into effect in 2020.

The Secretary-General asserted that the world may have only five years to take measures needed to meet the most ambitious target of keeping global warming at 1.5C, the recommended target by an independent panel of scientists.

Mr Guterres said world leaders should "show courage in combating entrenched interests" in climate change.

It appears to have been a thinly veiled criticism of the US delegation’s appearance at the conference.

The US remains the sole country that has initiated withdrawal procedures from the deal, which unless stopped will go into effect on 4 November 2020.

On 13 November the official US delegation - half the size of what it has been in the two previous Obama administrations - held an event during which industry representatives from coal, oil/gas, and nuclear power were prominently featured.

The presentation was interrupted for nearly 10 minutes by youth activists chanting and singing.

Activists are a common presence at the UN meeting every year, but this time their ire was in full force opposing the US’ starkly different message from the rest of the world, several people attending the meeting told The Independent.

During the panel Trump international energy issues advisor George D Banks said it was “controversial only if we chose to bury our heads in the sand.”

“Without question, fossil fuels will continue to be used, and we would argue that it’s in the global interest to make sure when fossil fuels are used that they be as clean and efficient as possible,” Mr Banks said.

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As the New York Times reported, “the American presentation came the same day that a new study showed that [carbon] emissions were rising worldwide after three years on a plateau.”

Mr Guterres also said: “it is fitting that this conference is led by Fiji, a nation on the front lines” of climate change.

“When the front line is decimated, the whole army is lost,” said Mr Guterres.

Small island nations issues with sinking amid rising sea levels and the damage after several recent hurricanes in the Caribbean have gained particular prominence at this year’s talks.

In another apparent criticism of Mr Trump, he said about the idea of coupling economic growth with use of fossil fuels: “today that dogma is dead”.

Mr Trump had said the reason for US withdrawal from the accord was because it put American workers at an “economic disadvantage.”

Mr Guterres pointed to the rapid growth of India and China, while becoming leaders in solar power, as well as the increase in carbon markets - or places for companies to trade emissions credits as an incentive to go ‘green’ - as evidence.

Conference participant Simon Chin Yee, a research fellow for the European Centre for Energy and Resource Security, told The Independent that observers will “need to watch countries that were trailing their tails going into” the conference during which the Paris accord was signed.

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Those who were on the fence about making large cuts to their carbon emissions rates though they signed the agreement may “use the US withdrawal as an excuse to stall the negotiations” on how best to implement the agreement as well as make concrete financial commitments, Mr Chin Yee explained.

Germany, Australia, and Japan are just some of the world’s developed countries that have been criticised by activists and scientists for still using coal. Norway still attributes a significant portion of its GDP to oil reserves.

Mr Chin Yee said the key to considering the meeting a “success” despite the impending withdrawal of one of the world’s worst polluters is for countries to come together on how to implement the agreement as soon as possible.

Another American delegation also made an unofficial appearance in Bonn.

California Governor Jerry Brown, former New York City Mayor and UN special envoy on cities and climate change Michael Bloomberg, and former Vice President Al Gore were all in attendance at a pavilion outside of the official conference venue.

The purpose of the pavilion and its exhibitions is to showcase how Americans - at the sub-national level - are still fighting climate change in spite of the Trump administration’s efforts to dismantle Obama-era environmental regulations domestically.

Part of the “We Are Still In” coalition, it claims to represent more than 130 million Americans and $6.2 trillion of annual economic output.

Republicans and Democrats alike make up the coalition, which has more than one thousand CEOs, mayors, and governors in the US.