Friday, November 17, 2017

Second hottest October on record, just above October 2016

Summary: October 2017 was the second hottest October on record. The 12 month period to October 2017 was the second hottest November to October period on record.

According to GISS NASA, the average global surface temperature anomaly for October was 0.90 °C, which is 0.18 °C less than the October 2015. October 2017 was just 0.01 °C hotter than the next hottest October in 2016.

Below is a chart of the average of 12 months to October each year. The 12 months to October 2017 averaged 0.90 °C above the 1951-1980 mean, which was 0.13 °C cooler than the 12 months to October 2016.

This makes it the second hottest September to October 12 month period on record.

Figure 1 | Global mean surface temperature anomaly for the 12 months to October each year. The base period is 1951-1980. Data source: GISS NASA

Next is a chart of the month of October only. This October was 0.90 °C above the 1951-1980 average and was the second hottest October on record. It was 0.18 °C cooler than October 2016, which was 1.08 °C above the 51-80 mean. Hover over the chart to see the anomaly in any October:
Figure 2 | Global mean surface temperature anomaly for the the month of October only. The base period is 1951-1980. Data source: GISS NASA

ENSO year comparisons

In the chart below you can see the global mean temperature trend by month. It shows the strongest El Niño years since 1950, which were followed by a La Nina. I've included the 2015-17 period for comparison. The BoM ENSO update is now showing La Nina watch. It's not made the global temperature drop yet, however.

Of the seven very strong, strong and strong to moderate El Ninos since 1950, there were only three that were followed by a La Nina (not including 2015-17, when there was no La Nina).

The chart below spans a three year period. That is, for the 2015-16 El Niño and subsequent, it goes from January 2015 to December 2017, or would if the data allowed. (For a more detailed explanation see the HW articles: El Niño to La Niña years with more detail here.)

Figure 4 | Global mean surface temperature for strong or moderate/strong El Nino years that were followed by a La Nina. Also includes the 2015/16 El Nino for comparison. Data source: GISS NASA

Year to date chart

For the record, here is the year to date progressive chart. You need to understand what it is to make sense of it. The chart below shows the average temperature for the year at each point on each separate line on the chart. The topmost line is last year (2016). At January, the point is just the anomaly for January. At February, the point is the average anomaly for January and February. At October, it's the average of January to October inclusive - all the way to December, which is the average for the whole year.

So the 2017 year shows that the average for the period January to October is 0.91 °C. This is 0.11 °C lower than the average for the year was this time last year at the end of the massive El Nino. The average over the entire 2016 year is 0.99 °C (the point marked for December on the 2016 line) so by now it's virtually impossible for this year to be another hottest year.

Figure 6 | Progressive year to date global mean surface temperature anomaly. The base period is 1951-1980. Data source: GISS NASA

The anomalies for the rest of the year would have to average more than 1.4 °C for 2017 to be hotter overall than last year. That won't happen. If the anomalies have an average of 0.67 °C or more then 2017 will end up hotter than 2015. In that case 2017 will be the second hottest year on record. That's quite likely even with a La Nina.


  1. On track to be probably the 2nd, definitely the 3rd hottest year on record, and a significant number of gumbies over at WUWT say it's cooling. Gee, it's so hard to know who to believe. I'm torn.

  2. Unless November warms up a lot in the last week of the month, it is looking to be a lot colder. JIASO PDO for October is still positive, barely.

  3. It could slip behind 2015 still. However November and December would have to have temperatures around those in 2012 or 2013. Not impossible, particularly with El Nino conditions. I'd still be betting it will be the second hottest, if I was forced to make a prediction :)

  4. Whatever happens, it will still be the hottest year w/o an El Nino, and that is saying something.

  5. I'm with Sou. I'd also bet on 2017 ending in second place after 2016, and either ahead of 2015 or tied with it.

    Did you notice though? As I predicted it might, July 2017 slipped behind 2016, and is now only the second hottest July on record (albeit by an insignificant margin). Not an earth-shattering prediction, but still, hey, I was right about something! I'll try not to let it go to my head. Also, thank you to all the little people who made this possible.

  6. This comment has been removed by the author.

  7. metzomagic, but this year is off from the hottest year ever, so that means that the global cooling that people like Patrick Michaels have been predicting for 15+ years is finally happening, right? (sarcasm)

  8. "2017 annual mean prediction updated using Oct data. Probability of ~94% it will be the 2nd warmest yr in the GISTEMP record."

  9. Art prices have been soaring too- In the aftermath of the Bonn climate conference one picture just went for the equivalent of 5 million tons of coal.

  10. Well, November is warming up now, it looks like that will continue to the last day, so it should finish slightly above the threshold for 2nd or 3rd warmest year.

  11. November numbers just came in at +0.87 C. Even with September being revised down a bit, 2017 looks like a lock for the 2nd hottest year on record. For the seasonal year (Dec - Nov), 2017 finished in 2nd by a comfortable margin.

  12. Global cooling!!1!!eleventy one!!


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