The independent analyses by NASA and The National Oceanic and Atmospheric Administration (NOAA) showed that globally, 2018's temperatures rank behind those of 2016, 2017 and 2015 and the past five years are, collectively, the warmest years on the modern day record.
This story is developing.
According to NASA's Goddard Institute for Space Studies (GISS), the global temperature for 2018 was 1.5 degrees Fahrenheit warmer than the mean global temperature for the years 1951-1980. Using much of the same data, NOAA estimates that global temperatures were 1.42 degrees Fahrenheit (0.79 degrees Celsius) higher than the 20th-century average.
The polar vortex event last month that saw record lows across the American Midwestern states, leading to several deaths, is a result of a weakening of the jet stream and the kind of weather event that scientists fear will become more frequent as the temperature in the Arctic continues to rise.
"There's no question about those trends existing however we slice it and our understanding of why those trends are occurring is also robust", Gavin Schmidt, director of NASA's Goddard Institute for Space Studies in NY said Wednesday.
NASA and NOAA added that increasing temperatures can also contribute to longer fire seasons and some extreme weather events.
"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 of the agency's medium-term forecasts.
The United Nations says the world is now on track for a temperature rise of 3C or more by 2100.
That warming is causing significant changes in the Arctic, especially where the loss of sea ice continued in 2018 as it has in years prior, contributing to sea-level rise.
US President Donald Trump, who has cast doubt on mainstream climate science and promotes the coal industry, plans to withdraw the United States from the Paris Agreement.
He did not mention climate change in his State of the Union speech on Tuesday.
He called for more, greener investments, ranging from defences against rising seas to drought-resistant crops.