In this specific graph NASA compares global temperatures to the base line temperature of 1880 to 1899, when the fossil fuel burning was much less than today. With this reference period 2015 was warmer by 1.95 degrees Fahrenheit.
The global time lapse from 1970 shows that 2015 warming is a continuation of a long term trend of global warming.
Looking back at just the month of December, 2015, 29 US states had the warmest December on record by nearly 6 degrees F, and parts of Europe also had a record warm December.
TAG: The current El Niño has played a part in the warming, but 2015 would be a record with or without El Niño.