Temperature Update, December 2017, GISTEMP

We now have all the data for 2017 from all surface data sets, but I'll stick to the schedule of a single post for each set I'm tracking. So this post will look at GISTEMP and there will be another looking at HadCRUT. (And at some point I might get back to writing proper debunking posts.)

2017 from NASA

NASA's GISTEMP for December 2017 has been announced with a press release. This shows to little surprise that 2017 was the second warmest year in their data set, and also mentions that NOAA has it as 3rd warmest. They also remind us that individual rankings of years are not that important, and the main message is that the long term trend is continuing.

December

The GISTEMP anomaly for December was 0.89°C, compared to the 1951-1980 base period. This makes it the 2nd warmest December on record, with the last 4 years having the 4 warmest Decembers.

The mean anomaly for the year was 0.9°C, making 2017 the second warmest year in the GISTEMP record. The last 4 years have been the 4 warmest on record.

Annual anomalies for GISTEMP since 1979.

Annual anomalies for GISTEMP since 1880.

Forecasts

Note - as always references to previous forecasts are based on recalculations using the latest data. They may differ slightly to the published forecasts.

Based on data up to November I predicted that 2017 would be 0.892 ± 0.025°C. The actual result was 0.897°C. A difference of 0.005°C.

Here's how the forecast would have changed each month, compared to the actual annual value.

I'd say the GISTEMP forecasts were pretty successful. They were always within 0.03°C of the actual annual figure. For comparison, in March the average of the first three months was 1.067°C, my forecast would have been 0.915°C.

This graph compares the new and old models.

For most of the year the old model was better than the new. After August there was little to choose between the two. More importantly the confidence was much higher throughout.

As with the satellite data this should not be taken as too much evidence that the newer model is better. As we will see the results are quite different for HadCRUT.

Temperature Update - December 2017, RSS

The RSS satellite data has been released for the end of 2017, so here is my summary.

Temperatures

According to RSS 4.0 the anomaly Lower Troposphere was 0.59 °C in December, compared with the 1979-1998 reference period. This makes December 2017 the 2nd warmest December in the RSS data set.

Here's the traditional 12 month smoothed average.

This leaves the average anomaly for 2017 as 0.634°C, making 2017 the 2nd warmest year on record, beating only by 2016.

predictions

Last month the prediction was for 2017 to finish with an anomaly of 0.627 ± 0.027°C. The reported value is 0.634°C, 0.007°C warmer than predicted, well within the prediction interval.

This graph shows a month by month summary of the predicted annual value, along with a gray ribbon showing the 95% prediction interval. (Note, as always these predictions are recalculated with the current data.)

As with the UAH predictions, my model consistently underestimated the final figure, but it was within the prediction intervals for each month.

Here is the comparison with the method I was using in 2016.

As with UAH, the new method which includes an assumed linear trend, was consistently better than the old method, which only looked at the year to date temperatures. Not only was the new method closer to the actual value, especially at the start of the year when it roughly halved the error, but it also gave tighter prediction intervals. (With the UAH predictions there was not much difference in terms of the prediction intervals. I suspect this is due to UAH having less of a linear warming trend.)

Temperature Update - December 2017, UAH

Dr Roy Spencer has released the final 2017 month's figures for the UAH Global Temperature satellite data. Here I'll give some analysis of the year and see how well my predictions did.

December 2017

The anomaly for December was 0.41°C, compared with the 1981 - 2010 base period. This is a larger anomaly than November, and is the 2nd warmest Decembers on record.

This means the 12 month rolling average continues to rise slightly.

The average anomaly for 2017 finished at 0.375°C. This was the third warmest on record, beaten only by 2016 and 1998, both of which were strong El Niño years. 2017 was the warmest non-el Niño year.

Forecasts

In November I was forecasting 2017 would be 0.365 ± 0.028°C, with a 98.3% chance of finishing 3rd warmest. The actual average was 0.375°C, 0.01°C warmer than forecast, but well within the 95% confidence interval.

The following graph shows how the forecast would have changed each month. The blue dashed line shows the actual anomaly for 2017. The gray band shows the 95% prediction interval for each month.

The forecast underestimated the actual result every month, but the result was within the 95% band each month, though only just for some months. The fact that 2017 finished higher than forecast reflects the surprising warming seen in later months in the satellite data.

The least accurate forecast was in January with a forecast of 0.29°C, 0.085°C below the result. The actual cumulative average would have been a better forecast in each month, which effectively means my model was continually expecting temperatures to decrease when in fact they continued to rise.

Comparison With Previous Method

Last year I used a simple method to forecast the annual temperature. This simply compared the year to date value with previous years.

This year I tried a slightly more complicated model, that included both the year to date value and the year on year trend trend. Testing had suggested this should be a better fit, but I was interested to see how the two methods compared this year. This somewhat messy graph compares the old and new methods against the result for 2017.

The new method was consistently better than the old. I wouldn't read too much into this, as a lot will depend on how close any specific year is to the trend. In this case 2017 was quite a bit warmer than the trend would suggest, but at the same time the start of the year was a lot cooler than the end. Both methods were expecting the year to stay cooler than it did, but the new method just won out.

Temperature Updates - November 2017 - HadCRUT

A Christmas present from the Met Office and Hadley Centre as they release the November HadCRUT data early.

This shows the anomaly in November to be 0.547°C, compared to the 1961 - 1990 base period. This is slightly cooler than last November, and in contrast to GISTEMP and BEST is only the 10th warmest November on record.

This is much more like the pattern for November in the NOAA data set. The differences between the different data sets possibly is due to the extend different sets cover the Arctic.

The 12 month rolling average for HadCRUT looks like this.

The average anomaly for 2017 so far is 0.685°C, down from 0.699°C up to October. My prediction for 2017 is now 0.681 ± 0.026°C, compared with last months prediction of 0.692 ± 0.041°C.

As can be seen from the graph it's difficult to see HadCRUT finishing anywhere other than 3rd warmest. In fact my statistical model makes this 100% certain.

HadCRUT4

Rank	Year	Anomaly	Probability	Change
1	2016	0.8	0.00%	-0.00%
2	2015	0.76	0.00%	-0.05%
3	2014	0.58	100.00%	+0.05%

I'm not going to disagree with that. December could be anywhere from -0.57 to +1.63°C, and 2017 would still finish 3rd.

December Round Up

With all the data sets I follow updated to November we have a pretty clear view of where 2017 will finish. GISTEMP, BEST, and RSS will probably finish 2nd warmest, with only an outside chance of dropping to 3rd. NOAA, HadCRUT, and UAH will probably finish 3rd warmest, with only UAH having a small chance of finishing 4th.

Temperature Update - November 2017 - GISTemp

NASA's released the latest GISTEMP data.

The anomaly for November was 0.87°C compared with the 1951 - 1980 base period. This is down slightly from 0.90°C in October. This is the 3rd warmest November on record. The last three Novembers have been the three warmest Novembers on record.

It is extraordinary how much warmer the last three years have been in November compared with any previous year. The equal 4th warmest Novembers were 2010 and 2013, and they were almost a tenth of a degree cooler than this current month.

The 12 year rolling average continues to cool from the el Niño peak.

The cumulative average for 2017 is virtually unchanged, down to 0.901°C from 0.904°C up to October.

Forecast

My forecast for 2017 is now 0.895 ± 0.025°C, compared with the forecast from October of 0.897 ± 0.04°C.

It is increasingly likely that this will be the 2nd warmest year on record. In any event 2017 will be very close to 2015, two very warm years sandwiching a much warmer year.

GISTEMP

Rank	Year	Anomaly	Probability	Change
1	2016	0.99	0.00%	-0.00%
2	2015	0.87	97.99%	+5.38%
3	2014	0.73	2.01%	-5.38%

For 2017 to drop to 3rd place will require December to drop to around 0.53°C. The last time a December was this cool was 2012.

Other Data Sets

I'm not giving detailed monthly updates on BEST and NOAA, but with one month to go here's a brief update on them.

BEST is very similar to GISTEMP. November was also the third warmest on record, and it is also shows 2017 on track to be second warmest, with similar (slightly better) odds to GISTEMP.

NOAA has a somewhat cooler month with November 2017 being identical to 2016 at equal 5th warmest. According to my statistical model NOAA is now 100% certain to finish 3rd warmest, and looking at the graph it is easy to see why.

As with HadCRUT the fact that NOAA is finishing in a different position to GISTEMP and BEST has more to do with how warm 2015 was than with a big drop in 2017.

Temperature Update - November 2017, RSS

As with UAH, the Remote Sensing System satellite lower troposphere data shows a big drop in the anomaly from October to November.

Details

The anomaly for November was 0.549°C compared to 0.805°C in October (anomalies relative to the years 1979 - 1998). This still makes this November the third warmest November, with the last three Novembers being the warmest three in the data - with all three being over 0.1°C warmer than the previous warmest November.

The cumulative average for the year dropped slightly, from 0.646°C to 0.637°C.

Here is the updated 12 month rolling average.

Predictions

My prediction for 2017 is unchanged from that for October, but with more confidence. The expected average for 2017 is 0.624 ± 0.028°C, compared with last months prediction of 0.624 ± 0.043°C.

Baring a major catastrophe it seems certain RSS will have its second warmest year on record, the warmest being last year.

RSS 4.0

Rank	Year	Anomaly	Probability	Change
1	2016	0.74	0.00%	-0.00%
2	1998	0.58	99.86%	+2.16%
3	2010	0.57	0.13%	-1.58%
4	2015	0.54	0.01%	-0.56%
5	2005	0.43	0.00%	-0.03%

My statistics suggest there is less than a 1 in 700 chance of RSS not finishing 2nd. But this would require December to have a negative anomaly (around -0.041°C). The last time December was this cold was 1995. There have only been 3 months during the 21st century this cold.

Temperature Update November 2017 - UAH

Dr Roy Spencer has released the November 2017 global temperatures for the UAH 6 lower troposphere satellite data set. This shows a big drop in the anomaly compared to last month's record breaker, but still pretty warm.

Details

The anomaly in November was 0.36°C compared to 0.63°C in October, and down a tenth of a degree from last November. However, this still makes 2017 the 2nd warmest November in the UAH data set. The last three years have had the three warmest Novembers in the set.

The mean of the first 11 months of 2017 is 0.372°C compared with 0.373°C for the first 10 months.

The 12 month rolling average is beginning to move down slightly from its unexpected jump upwards, but I expect it should start moving down more over the next year as La Ni&ntilda;a takes hold.

Predictions

With just one month of 2017 to go, my simple statistical analysis predicts 2017 will finish at 0.364 ± 0.028°C, compared with last months prediction of 0.359 ± 0.043°C.

This has made it far more likely that 2017 will finish as the 3rd warmest year, with less than a 1 in 50 chance of dropping below 2010 for 4th place.

Probability of different rankings for UAH 6.0
based on data to November 2017

Rank	Year	Anomaly	Probability	Change
1	2016	0.51	0.00%	-0.00%
2	1998	0.48	0.00%	-0.00%
3	2010	0.33	98.30%	+10.02%
4	2015	0.27	1.70%	-10.02%

However, I suspect this is too certain. For 2017 to finish below 2010, December would only have to drop to around 0.13°C. This would be equal to December 2013 and 2012, so with temperatures dropping from the very high values of the last few years it doesn't seem that unlikely. In any event, it's clear that 2017 will be another hot year, similar to 2010, hotter than 2015, and the hottest El Niño year that was not a major El Ninño.

How remarkable the last few years have been is much clearer if rather than focusing on one calendar year, we look at 2 yearly averages.