Temperature Update - December 2017, HadCRUT

The Met Office Hadley Centre have released their HadCRUT4 data for December 2017. Here is my monthly update describing what that means for the year, and looking at how well my forecast models performed over the year.

Temperatures

The HadCRUT anomaly for December 2017 was 0.585°C compared with the 1961 - 1990 base period. This was the 6th warmest December in its record. Five of the warmest seven Decembers have occurred in the last five years. The other two where in 2003 and 2006, with the 2nd warmest being in 2006.

The mean anomaly for 2017 was 0.68°C, making 2017 the 3rd warmest year in the HadCRUT record. The last four years have been the four warmest on record.

HadCRUT4 annual anomalies since 1979

HadCRUT4 annual anomalies since 1850

Forecast analysis

My prediction for 2017 based on data up to November would have been 0.680 ± 0.026°C. The actual average for 2017 to 3 decimal places is 0.676°C.

This graph illustrates the changing predictions for each month, along with the 95% prediction interval.

This was not as good as for GISTEMP. For much of the year the forecast was around 0.05°C too warm. For HadCRUT the old model was better than the new, though the better confidence still suggests the newer model is better.

Final Thoughts

Both NOAA and BEST have also released their year end reports, with 2017 coming in respectively 3rd and 2nd warmest.

This means all of the main global temperature data sets, both surface and satellite, put 2017 as one of the three warmest years on record, with 2016 being the warmest. What makes 2017 unusual is that it was not an El Niño year.

But although the last few years have been extraordinary in terms of the global temperatures, they should not come as a surprise. They are not that unusual in relation to the trend seen since the 1970s. A few years ago there was a run of years below the trend, now we have had a run of years above the trend line. This is to be expected. But they should be a shock to anyone who used a few cooler years to claim global warming had stopped at the start of the century.

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.