Bernie Sanders said Wednesday that "climate change is real" and the "debate is over" after NOAA reported that 2015 was the hottest year on record.

While a warming El Nino trend likely played a role in 2015 setting the new record, Schmidt says, "it is the cumulative effect of the long-term trend that has resulted in the record warming that we are seeing".

Last year wasn't just the Earth's hottest year on record - it left a century of high temperature marks in the dust.

Jake Crouch, climate scientist at NOAA's National Centers for Environmental Information, added: "At this point we're virtually certain that 2015 will be the warmest year on record".

And of course, thanks to El Niño, 2015 went out guns blazing: December 2015 was the most anomalously hot month of any in history, at 1.11°C (2.00°F) warmer than its monthly average.

"2015 was by far the hottest year on the records we've put together", Gavin Schmidt, director of NASA's Goddard Institute for Space Studies said in a press conference this morning. NASA, which measures differently, said 2015 was 0.23 degrees warmer than the record set in 2014 and 1.6 degrees above 20th century average.

"Climate change is the challenge of our generation", said NASA Administrator Charles Bolden.

NASA and the National Oceanic and Atmospheric Administration (NOAA) announced the news on Wednesday morning, after both agencies separately analyzed global temperature data and came to the same conclusion.

That makes 2015 the hottest since instrument records began being kept in 1880, beating the record set in 2014 by 0.29°F (0.16°C). The organizations used measurements of global average temperatures taken during the past 135 years. Meanwhile, all of the 10 hottest years on record have happened since 1997.

The hard fact is, according to scientists: climate change is driving these records, and the driver behind them are man-made emissions.

"That's the first time we've seen that", Karl told ABC News.

Meanwhile, ten of 2015's monthly global tempuratures broke or tied with existing global heat records, too, the agencies announced.

Global warming is, of course, the main reason why the record for the warmest year keeps being broken.