September was the seventh month this year to go down in the record books as the hottest on record dating to January 1880. February, March, May, June, July and August are the other months this year that were the warmest on record. In addition, January was the second warmest and April was the third warmest in the period of record.
Last year, 2014, was the warmest year on record, but it could be surpassed by 2015 after all data is compiled at the end of the year.
El Niño and climate change are both playing a role, according to Dr Jeff Masters of Weather Underground.
Click through to see the effects of this year's El Niño:
El Nino's effects
With record-breaking September, 2015 continues pace as warmest year on record
NOAA has released an update to its El Niño advisory. This image shows the satellite sea surface temperature departure for the month of October 2015, where orange-red colors are above normal temperatures and are indicative of El Niño. This event is forecast to continue through the winter, likely ranking as one of the top 3 strongest events since 1950, before fading in late spring or early summer. El Niño has already produced significant global impacts, and is expected to affect temperature and precipitation patterns across the United States during the upcoming months. Seasonal outlooks generally favor below-average temperatures and above-median precipitation across the southern tier of the United States, and above-average temperatures and below-median precipitation over the northern tier of the United States. (Photo via NOAA)
MAKASSAR, SOUTH SULAWESI, INDONESIA - SEPTEMBER 21: Two girls are seen walk behind of dried up ricefield at Manggara Bombang village, Maros district on September 21, 2015 in Makassar, Indonesia. Indonesia's national disaster management agency has declared that the majority of the country's 34 provinces are experiencing drought caused by the El Nino weather phenomenon, the worst drought in the past five years. The dry season forces villagers to walk long distances to find clean water. (Photo by Agung Parameswara/Getty Images)
NOAA issued an update to the El Niño analysis on September 10, 2015, in which forecasters from the Climate Predication Center say a strong El Niño is in place and likely to peak in late fall/early winter, and gradually weaken through spring 2016. This image shows the satellite-based average sea surface temperature data from the week of August 31 - September 6, 2015. Blue areas are cooler than the 1981-2010 average; red areas are warmer than that historical base period. The large pool of warmer than average temperatures along the equatorial Pacific is indicative of the El Niño conditions. (Photo via NOAA)
Sea surface temperature anomalies in November 1997 (left) compared to July 2015 (right). (Photo via NOAA)
A couple tries to cool off from the heat caused by El Nino with water overflowing from a defunct but still watery reservoir called the Wawa dam in Montalban in Rizal, east of Manila on February 21, 2010. El NiÃ±o was expected to dehydrate the Metro Manila area over in the next two months, according to the Philippine Atmospheric Geophysical Astronomical Services Administration (Pagasa). Earlier this month the government warned a possible drought caused by the El Nino weather system could slash Philippines rice yields this year. AFP PHOTO / NOEL CELIS (Photo credit should read NOEL CELIS/AFP/Getty Images)
Tons of dead fish are seen on the banks of the Solimoes River due the water's low level, November 25, 2009 near Manaquiri, 120Km from Manaus. The dry season, affected by the weather phenomenon EL Nino, is worse this year. According a study from Brazil's universities USP,UNICAMP,UFRJ and Embrapa, the country could lose some USD 3.6 billion over the next 40 years. AFP PHOTO / ANTONIO SCORZA (Photo credit should read ANTONIO SCORZA/AFP/Getty Images)
Heavy clouds covers Indonesia's capital city of Jakarta on November 29, 2009. The month of November ends the dry season and starts the wet period but the weather bureau anticipates El Nino's dry spell to affect Indonesian weather. AFP PHOTO / Bay ISMOYO (Photo credit should read BAY ISMOYO/AFP/Getty Images)
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"A potent El Niño event in the Eastern Pacific that crossed the threshold into the 'strong' category in early July continues to intensify, and strong El Niño events release a large amount of heat to the atmosphere, typically boosting global temperatures by at least 0.1 degrees Celcius," Masters writes. "This extra bump in temperature, when combined with the long-term warming of the planet due to human-caused emissions of heat-trapping gases like carbon dioxide, makes it virtually assured that 2015 will be Earth's second consecutive warmest year on record – with 2016 a good bet to exceed even 2015's warmth."
NOAA said September 2015 had the greatest departure from average of any of the 1,629 months in the period of record dating to January 1880. It beat out the previous record warm September set in 2014 by a margin of 0.12 degrees Celcius (0.19 degrees Fahrenheit).
The Ontario province of Canada had its warmest September on record, while the United States saw its second warmest September.
It wasn't warm everywhere though. Spain saw its coolest September since 1996. The United Kingdom was also cooler than average, with England and Wales seeing their coolest September since 1994.
El Niño's influence also showed up in the precipitation departures from average for September.
Australia recorded its third driest September in 116 years of records. During strong El Niño events, eastern Australia typically sees below-average rainfall, NOAA says.