UN Secretary-General Antonio Guterres said climate change is an absolute priority and the world is not doing enough.
"Climate change is the defining issue of our time, and we are at a defining moment," Guterres told an informal high-level leaders dialogue on climate change on the sidelines of the high-level week of the UN General Assembly.
"Many times journalists ask me what are my priorities. I always say we have many priorities in the UN... but I would say that this (climate change) is the absolute priority."
The Paris Agreement, which aims to keep global temperature rise to well below 2 degrees Celsius above pre-industrial levels and to keep the increase to 1.5 degrees if possible, represents the bare minimum to avoid the worst impacts of climate change, said Guterres.
The Paris Agreement commitment was universal. But the world is nowhere to where it needs to be to meet these minimum targets, said Guterres. "Climate change is indeed running faster than we are, and we have the risk to see irreversible damage that will not be possible to recover if we don't act very, very quickly."
According to a UN study, the commitments made so far by parties to the Paris Agreement represent just one-third of what is needed, he noted.
"We need to do more and we need to do it quicker: we need more ambition and accelerated action by 2020. If we do not reverse the current trend of emissions by 2020, it may be impossible to meet the 1.5 degree goal."
The effects of climate change are already being felt, with disastrous consequences for people and all the natural systems that sustain life in the planet. Just last year, the economic costs of climate-related disasters hit a record of 320 billion U.S. dollars, he noted.
Climate action makes moral sense, and also makes business sense, he said. "So why is climate change faster than we are? The only possible answer is that we still lack strong leadership to take the bold decisions needed to put our economies and societies on the path of low-carbon growth and climate resilience."
Guterres called specifically on the countries that account for the majority of greenhouse gas emissions to do more.
He asked for stronger leadership from the Group of 20 countries, which combined account for around 80 percent of the global greenhouse emissions. "Only courageous leadership will make the goals of Paris a reality."
This means ending subsidies for fossil fuels and high-emitting agricultural practices and shifting toward renewable energy, electric vehicles and climate-smart industry and agriculture. It means closing coal plants and replacing those jobs with healthier, better alternatives. And it needs carbon pricing that reflects the true cost of carbon emissions, he said.
He asked for increased investments and innovation in energy efficiency and renewable energy technologies across buildings, transport and industry.
Governments need to encourage their banks to support green financing and to encourage innovation in financial and debt instruments to strengthen the resilience of vulnerable nations such as small island states, he said.
It is also essential that governments fulfil their pledge to mobilize 100 billion dollars a year by 2020 for climate action, he said.
"The time is long gone when we could afford delay," he said. "Each day brings further evidence of the mounting existential threat of climate change to the planet. Every day that we fail to act is a day that we step a little r toward a fate that none of us wants -- a fate that will resonate through generations in the damage done to humankind and to life on Earth."