The UN weather agency is predicting an 80 per cent chance that average global temperatures will surpass the 1.5 Celsius (2.7 Fahrenheit) target laid out in the landmark Paris climate accord within the next five years.

The World Meteorological Organisation said Wednesday that the global mean near-surface temperature for each year from 2024 to 2028 is expected to range between 1.1 and 1.9 degrees Celsius hotter than at the start of the industrial era.

It also estimated that there's nearly a one-in-two chance — 47 per cent — that the average global temperatures over that entire five-year span could top 1.5 C, an increase from just under a one-in-three chance projected for the 2023-2027 span.

The report was cited in a sweeping speech about the threat of climate change by UN Secretary-General António Guterres to mark World Environment Day.

Meanwhile, the European Union’s climate service says last month marked the hottest May ever, capping 12 straight months of average monthly temperature records amid high and rising concerns about global warming.

The EU’s Copernicus climate change service, a global reference for tracking world temperatures, cited an average surface air temperature of 15.9 C (60.6 F) last month — or 1.52 C higher than the estimated May average before industrial times.

The burning of fossil fuels — oil, gas and coal — is the main contributor to global warming caused by human activity.