"The confirmation that we've exceeded the records for Carbon dioxide levels in the atmosphere indicates that the measures governments are now taking are not sufficient", Alberto Mataran Ruiz, who specialises in environmental science at the Spain's University of Granada, told Al Jazeera.
The talks unfold against a backdrop of rising public concern about climate change and a surge in protests, led by young people, calling on governments to step up action to rein in global warming and protect their citizens from its impacts.
And in Australia, students in Sydney and other cities walked out of class, saying more should be done to combat the country's bushfire crisis, which many see as a result of climate change.
Antonio Guterres said climate-related disasters were becoming more frequent and deadly.
Every year, air pollution associated with climate change kills seven million people, he noted, adding that human health and food security are at risk.
A UN Enviroment Programme report last week concluded that Carbon dioxide emissions would need to drop by a vertiginously steep 7.6 percent per year over the next decade to stay within that limit.
About two dozen green activists in the German capital Berlin symbolically jumped into the chilly waters of the Spree River in front of Parliament to protest against a government-backed package of measures which they say will not be enough to reduce the country's greenhouse gas emissions.
There's another big issue with the United States, which is pulling out of the 2015 Paris climate change agreement altogether.
Expressing concern about the "alarming rate" at which greenhouse gas emissions are growing, the United Nations chief highlighted The Production Gap's finding that the world is set to produce 120 percent more fossil fuels over the next decade than what is consistent with a 1.5-degree pathway.
But current national pledges - if carried out - would see global temperatures rise by at least 3 degrees C, a recipe for human misery, according to scientists.
Guterres did single out the European Union as playing a constructive role.
"The global shift from the grey to the green economy is gathering momentum", she said in a statement.
This year's conference aims to reach an agreement on some of the rules to implement the Paris Agreement, which have still been under discussion.
Speaking outside the local offices of Prime Minister Scott Morrison's Liberal Party, student Daisy Jeffrey said "people have lost their homes, people have lost their lives, we have to ask: how far does this have to go before our government finally takes action?"