Extreme weather events experienced in 2015 were unlike conditions seen before.
And to climate scientists, like Professor Will Steffen from the Australian National University, the hottest year since records began in 1880, is a milestone for all the wrong reasons.
"The records are tumbling faster and faster as we go along, they're being broken by larger margins, and this is showing us that the climate system is shifting to a much warmer state, at a very fast rate."
American agency, The National Oceanic Atmospheric Administration, or NOAA, found that in 2015, global temperatures across land and ocean surfaces, rose 0.9 degrees Celsius above the 20th century average.
And data from space agency NASA, found 2015 was 0.13 degrees Celsius higher than 2014.
NASA scientist Compton Tucker explains.
"Fifteen of the past 16 years have been the warmest years on record. And when you see a run like this, this is not something which people can easily dismiss and say it isn't true."
The University of Melbourne's Professor David Karoly says the rise in global temperatures is due to a couple of factors.
"It's partly due to natural climate variability, year to year climate variation, and the dominant factor in 2015 was the El Nino event."
But the current El Nino, associated with warm ocean temperatures in the tropical pacific ocean, wasn't the only driver.
Mr Compton says the majority of warming is because of human activity.
"This is due to the accumulation of carbon dioxide in the atmosphere, which acts as an insulating blanket around the earth and traps outgoing long-wave radiation."
The Bureau of Meteorology's also found 2015 to be Australia's 5th hottest year on record.
The nation's hottest October coinciding with an early start to the bushfire season.
Though we didn't set an annual record, Professor Karoly says an average global increase is still cause for alarm.
"There were a number of places, countries in the world, that weren't record hot, but in fact, Europe set a record high, parts of North America set very high temperatures, such as in December in the eastern parts of the United States."
He says with a waning El Nino for 2016, we can expect a continued increase in extreme heat events globally, but slightly wetter and cooler conditions for Australia.
