16 November 2011
Here is what NOAA/NCDC had to say about it:
- The combined global land and ocean average surface temperature for October 2011 was the eighth warmest on record at 14.58°C (58.14°F), which is 0.58°C (1.04°F) above the 20th century average of 14.0°C (57.1°F). The margin of error associated with this temperature is +/- 0.07°C (0.13°F).
- Separately, the global land surface temperature was 1.10°C (1.98°F) above the 20th century average of 9.3°C (48.7°F), making this the second warmest October on record. The margin of error is +/- 0.11°C (0.20°F).
All 8 of the warmest Octobers on record were in the last ten years according to NASA’s separate analysis here.