NASA has warned that the "impacts of long-term global warming are already being felt" - with last year's global surface temperatures the fourth warmest on record.
The administration said the global temperatures mark a continued warming trend, with last year's temperature 0.8C warmer than the average recorded between 1951 and 1980.
Collectively, the last five years were the warmest on record - with 2015, 2016 and 2017 all warmer than last year.
“2018 is yet again an extremely warm year on top of a long-term global warming trend,” said Gavin Schmidt, Director of NASAs Goddard Institute for Space Studies (GISS).
“The impacts of long-term global warming are already being felt - in coastal flooding, heat waves, intense precipitation and ecosystem change.”
The average global temperature has risen by about 1C since the 1880s - driven in large part by increased carbon dioxide and greenhouse gas emissions as a result of human activity.
The warming trends are strongest in the Arctic - with last year seeing continued loss of sea ice.
NASA said mass loss from the Greenland and Antarctic ice sheets is also continuing to contribute to sea level rise.
Mr Schmidt said the increasing temperatures are also known to contribute to longer fire seasons and extreme weather events.
The past 4 years have been confirmed as the 4 warmest years on record. The 20 warmest years on record have been in the past 22 years. Global average surface temperature in 2018 was approximately 1.0° C above the pre-industrial baseline (1850-1900). #stateofclimate #climatechange pic.twitter.com/BRwzME9N6Y
— WMO | OMM (@WMO) February 6, 2019
The World Meteorological Organization also confirmed that last year was the fourth warmest on record this afternoon.
Noting that 2015, 2016, 2017 and 2018 were the four warmest on record, it said the world is now nearly 1C above the pre-industrial baseline.
"The long-term temperature trend is far more important than the ranking of individual years, and that trend is an upward one," said WMO Secretary-General Petteri Taalas.
"The 20 warmest years on record have been in the past 22 years.
"The degree of warming during the past four years has been exceptional, both on land and in the ocean."
— NOAA (@NOAA) February 6, 2019
He warned that "temperatures are only part of the story."
"Extreme and high impact weather affected many countries and millions of people, with devastating repercussions for economies and ecosystems in 2018," he said.
"Many of the extreme weather events are consistent with what we expect from a changing climate.
"This is a reality we need to face up to. Greenhouse gas emission reduction and climate adaptation measures should be a top global priority."
The WMO noted that this year has kicked in where 2018 left off - with Australia experiencing its warmest January on record and "heatwaves unprecedented in their scale and duration."
The country is also experiencing a long-term increase in extreme fire weather, and in the length of the fire season.
The extreme heat in the southern hemisphere comes as the parts of North America experience extreme cold.
Mr Taalas said the unusual cold may be linked to the dramatic temperature changes in the arctic and increasing speed of ice melt.
"What happens at the poles does not stay at the poles but influences weather and climate conditions in lower latitudes where hundreds of millions of people live,” he said.
ðŸ’§January's #Copernicus #C3S #hydrological summary is out!
- The Alps - much above average snowfall
- Northern parts of eastern Mediterranean & northwest of Spain - rainfall much above average
- Australia, southern Africa & eastern Brazil very dry
More âž¡ï¸https://t.co/fuGGcBbazo pic.twitter.com/gUgBzJb0cu
— Copernicus ECMWF (@CopernicusECMWF) February 6, 2019