Weather limits in 2018 included fires in California and Greece, drought in South Africa and floods in Kerala, India.
Record levels of man-made greenhouse gas emissions, primarily from burning fossil fuels, trap ever more heat.
Average global surface temperatures were 1.0 degrees Celsius over pre-industrial times in 2018, said the UN World Meteorological Organization (WMO) based on data from US, UK, Japanese and European weather stores.
"The long-term temperature development is far more important than the ranking of the individual years, and this trend is upward," said WMO Secretary-General Petteri Taalas in a statement.
"The 20 hottest years on record have been in the last 22 years."
To combat warming, nearly 200 governments adopted the climate process in Paris in 2015 to phase out the use of fossil fuels and limit the temperature rise to 2 C over pre-industrial times, while the "pursuit of effort" for 1.5 C.
"The effects of long-term global warming have already been felt – in coastal floods, heat waves, intense rainfall and ecosystem changes," said Gavin Schmidt, director of NASA's Goddard Institute for Space Studies.
Last year, the United States alone had 14 weather and climate disasters with losses of over DKK 1 billion. Dollars each, led by hurricanes and fire birds, said the US National Oceanic and Atmospheric Administration (NOAA).
NOAA and NASA contribute data to the WMO.
This year has also started with burning temperatures, including Australia's hottest January on record.
Due to the global trend, parts of the United States suffered bone cooling colds from a flood of Arctic air last week.
In the WMO registers dating back to the 19th century, 2016 was the hottest year, enhanced by an El Nino weather event in the Pacific, by 2015 and 2017 by 2018 in the fourth.
Risks of 1.5 C
British Met Office, which also contributes data to the WMO, can raise the temperature to 1.5 C over pre-industrial times, for example, if a natural El Nino weather event adds a heat outbreak.
"Over the next five years, there is one in 10 chance that one of these years will break the limit (1.5C)," said Met Office professor Adam Scaife of Reuters of the agency's medium-term forecasts.
"It doesn't say that the Paris agreement is over for … but it's a worrying sign," he said. The United Nations defines 1.5C Paris temperature targets as a 30-year average, not a freak blip in a single year.
The United Nations says the world is now heading for a temperature rise of 3 ° C or more by 2100. The Paris Pact responded to a 1992 UN treaty, where all governments agreed to avert "dangerous" man-made climate change.
A UN report last year said the world is likely to break 1.5 C once in 2030 and 2052 on current trends triggering ever-increasing heat waves, heavy storms, droughts, mudslides, extinctions and rising sea levels.
US President Donald Trump, who has doubted the general climate science and promotes the coal industry, is planning to withdraw the US from the Paris agreement. He did not talk about climate change in his state of speech on Tuesday.
Patrick Verkooijen, head of the Global Center for Adaptation in the Netherlands, told Reuters that the WMO report showed that climate change is not a distant phenomenon, but is here right now.
He called for greener investments, from defense to rising sea to drought-resistant crops.