Wednesday, August 16, 2017

2017 has just had the hottest July on record!

Sou | 4:00 AM Go to the first of 7 comments. Add a comment

Summary: July 2017 was the hottest July on record by just a smidgen. The 12 months to July 2017 was the second hottest August to July period on record.

Because July is the hottest month, it also makes it the hottest month ever on record. Edit: it's been pointed out to me that August last year pipped July 2016 and July 2017 as the hottest month on record.

According to GISS NASA, the average global surface temperature anomaly for July was 0.83 °C, which is 0.01 °C more than the July 2016, making July 2017 the hottest July in the record.

Below is a chart of the average of 12 months to July each year. The 12 months to July 2017 averaged 0.92 °C above the 1951-1980 mean, which was 0.11 °C cooler than the 12 months to July 2016.

This makes it the second hottest August to July 12 month period on record.

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

Next is a chart of the month of July only. This July was 0.83 °C above the 1951-1980 average and was the hottest July on record. It was just 0.01 °C hotter than July 2016, which was 0.82 °C above the 51-80 mean. Hover over the chart to see the anomaly in any July:
Figure 2 | Global mean surface temperature anomaly for the the month of July 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 inactive, with no ENSO event likely this year.

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 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 3 | 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

Where was it hot?

In June it was very cold in much of Antarctica. It got relatively hot there again in July. Move the arrow at the left to the right to compare July with June.

June 17
May 17

Figure 4 | Maps showing mean surface temperature, anomalies for July and June, from the 1951-1980 mean. 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 July, it's the average of January to July 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 July is 0.94 °C. This is 0.13 °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 1.0 °C (the point marked for December on the 2016 line) so although it's not completely impossible for this year to be another hottest year, the next few months would have to be very hot for that to happen.

Figure 5 | 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 1.07 °C for 2017 to be hotter overall than last year. That seems highly unlikely. If the anomalies have an average of 0.77 °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 not impossible.


  1. Looking at the remaining months one would be very surprised if 2017 is not above 2014 and very close to 2015.
    Good to see your posting again Sou trust all is fine.

  2. Glad to see you back, Sou! I was very surprised to see 2017 storm back with a hottest month on record. That's impressive, whether or not it manages to hold on to that title. The difference with 2016 is insignificant, and the GISS data is often corrected by small amounts, sometimes months later. Case in point: when I looked at this data yesterday, the 2016, J-D anomaly was 0.99 C, but today it's a full 1.00 C. My memory isn't good enough to figure which month or months contributed to that change though.

  3. Thanks, Anon and Greg.

    The data changes slightly as more records come in. As you say, Greg, this can be some time later.

    The other factor is that GISTemp is now using ERSST v5 not v4.


  4. Echo above too

    presumably all the more surprising (worrying) as it is on the tail end of an el nino

    1. I'm confident the GWPF will redefine El Ninos to cover this.

  5. Shurely this cannot be true. It's been a very cool summer here. I was sure global cooling had begun.

    Actually it has been cool this summer. We seldom seem to be above 25C all summer.

    1. The ENSO disappeared in 2016. The tropical Pacific is showing no strong anomalies (http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/enso.shtml#discussion)


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