The only way 2015 will not be the warmest year in global recorded history, according to data from the National Oceanic and Atmospheric Administration, is if December is the coldest December in recorded history -- and is more abnormally cold than any month since data was first collected.
The NOAA measures each month against itself. So what's pictured above is how much hotter or colder each January or May or whatever was than the average of all Januarys or Mays in the 20th century. In September, we noted that the summer of 2015 was hotter globally than any summer on record.
Since then, 2015 has only gotten hotter. Here's what the final stage of the graph looks like now.
That's one way of picturing how hot it has been. Another is to color-code each month according to how much hotter or colder than average they have been since 1880 and let you scroll through. Like so.
In order for 2015 to not replace 2014 as the hottest year ever, December will need to be very, very cold. Very cold. Historically cold. In order for 2015 to simply drop to second, here's what December will need to look like:
Or, to go back to the original version of the chart, like this.
And that's simply to have 2015 be the second-hottest year on record. In order for 2015 to only be second-hottest, December needs to be more cold than any month has ever been -- 16 percent colder than the coldest month (relative to itself) on record: January 1893.
In other words, 2015 will be the hottest year on record.