Twenty warmest years "all in the last 22", scientists say in a United Nations report, with weather extremes in 2018 including wildfires in California and Greece, drought in South Africa and floods in Kerala, India. This is in part due, according to NASA, from increased emissions in the atmosphere of carbon dioxide and other greenhouse gases created by human activity.
"You get ups and downs - years that are a little bit warmer, a little bit cooler - but the long-term underlying trend is very, very clear", said NASA climatologist Gavin Schmidt, who worked on the space agency's analysis.
The results mean that, put together, the last five years have been the hottest ever recorded, according to NASA.
Each new year may not set a temperature record but the long-term warming "resembles riding up an escalator over time and jumping up and down while on that escalator", said Deke Arndt, chief of NOAA's climate monitoring division, referring to variables such as the El Niño pattern.
Since record keeping began in the 1880s, the average global surface temperature has risen around 2 degrees Fahrenheit (1 degree Celsius).
NOAA said the average temperature for the contiguous U.S.in 2018 was 53.5 degrees Fahrenheit, making it a warmer-than-average year for the 22nd year in a row. The following year, 2017, is ranked as the second warmest.
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The global climate record dates back to 1880, the year that it became possible to gather reliable and consistent temperatures around the Earth.
Increasing temperatures can "contribute to longer fire seasons and some extreme weather events", Nasa also warned.
"Over the next five years there is a one in 10 chance of one of those years breaking the (1.5C) threshold", Professor Adam Scaife of the Met Office told Reuters news agency of the agency's medium-term forecasts. It appears highly likely, at least from today's perspective, that the line will be crossed, despite the fact that 190 nations have signed the Paris climate agreement. Those higher temperatures continue to drive the decline in sea ice in the Arctic.
The records also show that the annual temperature of the Old Continent increased at an average rate of 0.12 Celsius degrees per decade since 1910, although it has nearly quadrupled to 0.43 Celsius since 1981.
While The eastern United States and parts of Canada are seeing record-breaking cold temperatures, Alaska and large parts of the Arctic have been warmer than average.
The data released by WMO confirm the urgency of addressing climate action - as emphasized by the recent Intergovernmental Panel on Climate Change (IPCC) special report on the impacts of global warming of 1.5°C above pre-industrial levels.