August 2017 is the second hottest August on record - the #climate is changing

Summary: August 2017 was the second hottest August on record. The 12 months to August 2017 was the second hottest September to August period on record.

According to GISS NASA, the average global surface temperature anomaly for August was 0.85 °C, which is 0.14 °C less than the August 2016. August 2017 was 0.05 °C hotter than the next hottest August in 2014, which had an anomaly of 0.80 °C.

Below is a chart of the average of 12 months to August each year. The 12 months to August 2017 averaged 0.91 °C above the 1951-1980 mean, which was 0.13 °C cooler than the 12 months to August 2016.

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

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

Next is a chart of the month of August only. This August was 0.85 °C above the 1951-1980 average and was the second hottest August on record. It was 0.14 °C cooler than August 2016, which was 0.99 °C above the 51-80 mean. Hover over the chart to see the anomaly in any August:

Figure 2 | Global mean surface temperature anomaly for the the month of August only. The base period is 1951-1980. Data source: GISS NASA

NASA GISS Seasonal Cycles

NASA GISS has recently started showing this chart, which is another way of looking at global temperatures. It is a plot of monthly temperatures over the year since 1880. The black dots show the months for 2017.

Figure 3 | GISTEMP Seasonal Cycle since 1880. 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 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

Where was it hot?

In July it was very hot in much of Antarctica, for Antarctica that is (which is a very cold place). In August some parts of Antarctica were much hotter than would be expected, while other parts were cooler. Move the arrow at the left to the right to compare August with July.

Figure 5 | Maps showing mean surface temperature, anomalies for August and July, 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 August, it's the average of January to August 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 August is 0.93 °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 °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 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 1.12 °C for 2017 to be hotter overall than last year. That seems highly unlikely. If the anomalies have an average of 0.75 °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.