This past October was nearly one degree Centigrade warmer than the average October temperature for the 20th century. It was just shy of a full degree — 0.98 degrees, to be precise — but it was still hotter by the largest amount in recorded history. A history that stretches back to 1880, we'll note.
The previous hottest month? September.
You can see the monthly anomalies on the graph below. For each month, the line indicates how much hotter or cooler it was than the average for that month.
The last time we had a cooler-than-average month was December 1984. In other words, in the era of the Cabbage Patch Doll. If you are 30 years old or younger, you've never lived through a month in which the global temperature was beneath the monthly 20th century average.
But, again: 2015 has been unusually hot. The National Oceanic and Atmospheric Administration, which collates this data, shows a map of the temperature difference across the globe. Here's October's:
Everywhere that's pink or red was warmer than normal; the areas of the darkest red set new records. There's a lot of darkest red.
You can see how much warmer this year has been if we look at the global map since October 2012.
Or, animated:
As we have noted before, 2015 will almost certainly end up being the hottest year in recorded history — beating the record set all the way back in 2014.
Does this prove that global warming is happening? No, it doesn't — any more than seeing a guy holding a smoking gun standing over a dead body in a locked room proves that the guy was the murderer. But it's awfully suggestive evidence.
