January and February 2016 smashed temperature records, the World Meteorological Organization (WMO) said on Monday as it warned climate change was advancing at an "unprecedented" rate.
Temperatures in the first two months of 2016 soared to new highs, following a year that broke "all previous records by a wide margin," the UN's weather agency said.
The WMO pointed to record 2015 land and sea surface temperatures, unabated sea-level rise, shrinking sea ice and extreme weather events around the world.
"The alarming rate of change we are now witnessing in our climate as a result of greenhouse gas emissions is unprecedented in modern records," the WMO's new chief, Petteri Taalas, said in a statement.
Dave Carlson, head of the WMO-co-sponsored World Climate Research Programme, said the rising temperatures this year were especially alarming, describing them as "a slap in the face."
'Relentless trend upwards'
"There is a relentless trend upwards," he told reporters in Geneva, saying the "startlingly high temperatures so far in 2016 have sent shockwaves around the climate science community."
2015 was the warmest year since 1880, according to the National Oceanic and Atmospheric Administration.
WMO confirmed findings by the National Oceanic and Atmospheric Administration (NOAA) last week.
The US agency determined that last month was the warmest February since modern records began, with an average temperature that was 1.21 degrees Celsius (2.18 degrees Fahrenheit) above the 20th-century average.
The hike in temperatures during the first two months of the year was especially felt in the far north, with the extent of sea ice in the Arctic at a satellite-record low in February, WMO said.
That is "quite a dramatic indication of climate change. We have never seen such an event before," Taalas told reporters in Geneva.
Carbon-dioxide concentrations in the atmosphere also crossed the threshold of 400 parts per million (ppm) during the first two months of the year, WMO said.
In 2014, CO2 levels had already risen to 397.7 ppm, which was 143 percent of levels prior to 1750, considered the start of the industrial era.
Monday's report came against a backdrop of the Paris climate talks in December. UN members enshrined a goal of limiting global warming to "well below" 2 C above pre-industrial levels, with a more ambitious target of 1.5 C if possible.
Arctic sea ice decreased to a record low in February 2016, according to satellite images.
But Taalas warned that the planet is already halfway to the 2 C milestone, with temperatures in recent months already nearly at 1.5 C.
"If you look at the number for the last couple of months, it is at 1.4 C," he said.
"Our planet is sending a powerful message to world leaders to sign and implement the Paris Agreement ... now before we pass the point of no return," he said.
"National climate change plans adopted so far may not be enough to avoid a temperature rise of 3 C," he said.
He stressed though that "we can avert the worst-case scenarios with urgent and far-reaching measures to cut carbon dioxide emissions."
The el-Nino climate phenomenon blamed in part for the soaring temperatures in 2015 and so far this year is meanwhile beginning to fade, Taalas said.
But Carlson stressed to reporters that the phenomenon "puts a lot of heat into the atmosphere ... that heat affects the global climate for a year or more" after it has died away.
"Typically a year following an el-Nino is a very warm year," he said.
But he said it would not be clear until October whether 2016 "will be warmer than 2015, whether it will be the record of all time."