On a visit to New Zealand, the UN head sent out a strong message that objectives in the Paris agreement would not be met amid "fading" political resolve.
UN Secretary-General Antonio Guterres launched a brief South Pacific tour in New Zealand Sunday, warning the world was "not on track" to limiting global temperature rises.
In a strong message for action on climate change, Mr Guterres said international political resolve was fading and it was the small island nations that were "really in the front line" and would suffer most.
His visit, ahead of the Climate Action Summit in September in New York will also take him to Fiji, Tuvalu and Vanuatu which are under threat from rising sea levels.
"We are seeing everywhere a clear demonstration that we are not on track to achieve the objectives defined in the Paris agreement," Mr Guterres said on the failure to limit rises to 1.5 degrees above pre-industrial revolution levels.
"And the paradox is, that as things are getting worse on the ground, political moves seem to be fading," he added in the joint press conference in Auckland with New Zealand Prime Minister Jacinda Ardern.
However, he did excuse New Zealand from his accusation, describing Wellington's leadership as "extremely important" after it introduced legislation to become carbon neutral by 2050, although greenhouse gas emissions from its economically vital agricultural sector will not have to meet the commitment.
Ms Ardern called climate change "the biggest challenge" facing the international community and said it would be "gross negligence" to avoid the issue.
During his three days in New Zealand, Mr Guterres will also meet with Muslim leaders in Christchurch to show solidarity following the March 15 massacre in which 51 people were killed by a lone gunman who attacked two mosques during Friday prayers.