180-Month HadCrut trends as of April month-end 2011
Posted by The Diatribe Guy on June 23, 2011
Today I present the 180-month charts using the most recent HadCrut data.
15 years starts to get to a point where some of those short-term cyclical variations start to get eliminated. Mind you, because I believe there are some clear longer-term cycles in the temperature data that span as long as 60 years, I think ANY trend line shorter than that has questionable value for extrapolation purposes.
The 180-month trend line is positive, with a slope of 0.0555, which translates to a temperature change of approximately one tenth of one degree Celsius over the course of 15 years. (Sounds like enough to melt a glacier or two, eh?) The current slope value of the 15 year trend line is actually at its lowest value since the period ending October 1994. The left side of the graph has some lower anomalies that will be dropping off over the next few months, and barring extremely high anomaly measures over the next few months, it is almost certain that the trend line slope will continue to decline for at least a bit.
In the chart below, we see the latest series of 15-year slope values since 2007. As noted above, we’re now at the lowest slope value in almost 17 years, and it has every likelihood of continuing lower. In fact, if I look forward and simply assume an average 12-month anomaly going forward for each month, this trend line will go negative in less than a year. That’s not a prediction, because I don’t know what the future of anomalies will bring, it’s just an observation. Still, it’s a fairly remarkable possibility that in the course of the next 10 months our “look back” negative trend line would go from just over 11 years to 15 years. We’ll just have to wait and see what happens.
The entire history of 180-month slopes is shown in the chart below, with the following observations:
1) Since 1960, there has very clearly been a continued positive trend measured in 15-year time increments. It’s too bad we don’t have good data prior to 1850 so we can see if there was a period of time where most of the trends were negative over a long span. If so, something seemed to “flip” around 1910. I suppose AGW proponents would point to this as the onset of CO2 emission expansion.
2) From October 1915 to November 1948 the 15-year trend line was positive. (33 years, 2 months)
3) From December 1948 to July 1959 the trend line was negative.
4) That period was followed by some fluctuation around zero.
5) The current stretch of positive trend lines began in May 1977. So, our current stretch above the zero trend is at exactly 34 years.