Digital Diatribes

A presentation of data on climate and other stuff

Temperature Trends for the last 360 months – HadCrut

Posted by The Diatribe Guy on May 23, 2012

Here are the latest charts for the HadCrut Global Temperature Anomalies, for the 30 year period ending March 2012.

The Data

What is presented here is the trend over the last 360 months, the slope of which has been in consistent decline over the last eight years. The current slope itself is +.1279. This puts the longer-term trendline of 30 years at a higher slope level than the 20 or 25 year magnitude. If one were to extrapolate this value forward as an expectation of continued warming, it would represent a 1.53 Celsius temperature increase per century. This spurred the question to me as to what starting point in time to current represents the highest current slope. The answer to that is using a starting point of January 1974 (37 years, 3 months), which has a current slope value of 0.13735. Cherry-picking that data point would indicate warming at a rate of 1.65 degrees Celsius per Century. All trend lines shorter than that (starting at least 4 months ago) or longer than than have a smaller slope value.

Chart below:

30 year Trend - HadCrut

Trend Line over Last 360 months – HadCrut

The next chart is simply a point of comparison. The highest slope value in recent years occurred with the 30-year period ending December 2003, at the height of global warming hysteria.

Recent Peak trend line

Peak 360 Month Trend Line

Finally, I show what has transpired with the slopes in recent years with the 30 year trend line. There has been a consistent decline in the slopes since November 2003 of the best-fitted lines. The decline itself is a very close linear fit though not quite as tight as some of the previous charts. There are periods of deceleration and acceleration in the trend, and even some periods where the slope value increases a bit for a time. Similar to the 25-year chart, in the most recent few months you can see it accelerate in its declining value. There is little indication that this decline will halt in the near term. I should explain how I arrive at that statement. I have a spreadsheet set up to emulate future periods, so by simply typing in prospective anomaly values, I can see what the level of the number needs to be in order to put an end to the declining slope values.

By way of exercise, here are the anomaly values needed to keep the slope the same from the current value to some period in the near future:
1) For the slope to remain level as of April 2012 month end, the next anomaly value has to be 52.
2) For the slope to remain level from April to May, the May anomaly needs to be 51.
3) For the slope to remain level from May to June, the June anomaly needs to be 60.
4) For the slope to remain level from June to July, the July anomaly needs to be 57.

None of these values are impossible. However, given the fact that last 20 anomaly readings are under 50, it would seem unlikely to expect such a series of values suddenly emerge.

Trend in recent 360-month slopes

Trend in recent 360-month slopes

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