- Jan 12, 2005
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How warm a month is is based on the difference between the month's average temperature compared with the historical average of the temperatures for that month, not on the month's absolute average temperature. By that standard, October 2015 was the warmest month in history, almost 1°C (NOAA's dataset) warmer than the average of all preceding Octobers. That's the greatest different for ANY month (relative to the historical average for that month) in history.
Here is a chart prepared by the Japan Meteorological Agency using its own dataset (in addition, it measures anomalies based on the average from 1981 to 2010, not the 20th-century average used by NOAA):
Because of the ongoing very large El Nino, which is expected to extend well into 2016, 2016 is expected to carry on where 2015 leaves off, which will tilt that red line upward a bit.
The combined average temperature over global land and ocean surfaces for October 2015 was the highest for October in the 136-year period of record, at 0.98°C (1.76°F) above the 20th century average of 14.0°C (57.1°F). This marked the sixth consecutive month a monthly global temperature record has been broken and was also the greatest departure from average for any month in the 1630 months of recordkeeping, surpassing the previous record high departure set just last month by 0.13°F (0.07°C). The October temperature is currently increasing at an average rate of 0.06°C (0.11°F) per decade.
Here is a chart prepared by the Japan Meteorological Agency using its own dataset (in addition, it measures anomalies based on the average from 1981 to 2010, not the 20th-century average used by NOAA):

Because of the ongoing very large El Nino, which is expected to extend well into 2016, 2016 is expected to carry on where 2015 leaves off, which will tilt that red line upward a bit.