The US National Oceanic and Atmospheric Administration (NOAA) has released a chart that illustrates how warm 2015 is, compared to the six other warmest years on record.
2015 is running away with the title of 'warmest year'.
The reason is a combination of global warming, and a strong El Nino event in the Pacific Ocean.
NOAA also released a comparison to all the years back to 1880, which is when the modern temperature record began.
It's also useful to look at years one by one in another way, colour-coded for El Nino, La Nina and 'neutral' years:
Every La Nina year since 1998 was warmer than every El Nino year before 1995.
Note that 2015 has not yet been added to that chart.