The warning was issued after the 12th successive month of broken temperature records globally with several parts of the planet suffering killer heatwaves.
It also came as Met Éireann confirmed last month was Ireland’s warmest May on record despite persistent cloud and low levels of sunshine.
February, March and April had higher than normal temperatures too despite rainfall also being above average.
United Nations secretary general Antonio Guterres said the world was at the “moment of truth” in relation to climate change.
He slammed fossil fuel companies as “the godfathers of climate chaos”, called for an international ban on fossil fuel advertising and sponsorship and challenged governments to show where their loyalties lay.
The fossil fuel industry was engaged in “shameless greenwashing” backed by “lobbying, legal threats and massive advertising campaigns”, he said.
“Billions of dollars have been thrown at distorting the truth, deceiving the public, and sowing doubt.
“It’s we the people versus the polluters and profiteers. It’s time for leaders to decide what side they are on.”
His remarks, in an address to mark World Environment Day, came as the World Meteorological Organisation (WMO) forecast an escalation of global heating between now and 2028.
That is despite the waning of El Nino, the cyclical phase of warm ocean currents that temporarily raises global temperatures above levels caused by climate change.
Flooding from El Niño rains in Kenya. Photo: Plan International Ireland
Currently, 2023 holds the record as the warmest year after a combination of climate change and a strong El Nino effect fuelled above average temperatures every single day.
Almost half of the days last year had temperatures more than 1.5C above pre-industrial levels, the period before the burning of fossil fuels soared and climate change accelerated.
The WMO now says temperatures are likely to breach the 1.5C threshold for a full year in at least one year by 2028.
That is despite indications that La Nina, a cooling influence on global temperatures, will take over from El Nino later this year.
Preventing temperature rise exceeding 1.5C is a core agreement of all but a handful of the world’s countries as it represents a critical point beyond which controlling the rate of climate change will become much harder.
The WMO says the expected overshoot of 1.5C would probably be temporary but exceedances are becoming more frequent.
There was one incident in 2015, one in 2016 and one in 2020. Last year saw breaches every second day and the last few months have followed that pattern.
A separate report from the EU’s Copernicus climate change service added that sea surface temperatures had now broken records for 14 straight months.
“The climate continues to alarm us. The last 12 months have broken records like never before,” said director, Samantha Burgess.
“Until we reach net-zero global emissions, the climate will continue to warm, will continue to break records and will continue to produce even more extreme weather events.”
