In my previous post, I discussed the jaded history of this month’s GISS anomaly, and some initial verbal comments.
In this post, I present some charts using the updated GISS numbers. The data source is found here. (And I just checked, and amazingly enough the numbers stayed the same from last evening’s post!)
Anyway, here we go…
Overall trend since 1880 is around 0.6 degrees per Century
We can extend a trend line back to December 2000 with a negative slope. All further extensions back are positive.
The current 60-month trend line is negative, though it has increased slightly since last month.
Here is the most recent peak value for a 60-month trend value for comparison against the current trend line.
This chart shows how the slopes have changed since the peak value. We have been in a period of declining slopes.
Here is the 120-month trend line as it currently stands.
This chart shows how the 120-month slope values have changed over time. We appear to be in a period similar to 1914-1947. The current similar period of constantly positive 120-month slopes started in 1979. If the cycle actually duplicates, we would cross into negative territory in 2012.
The decrease in 180-month slopes has been very steady. Note the r-squared fit of 0.9665. However, this is only since the beginning of 2007.
This chart shows the 180-month slope values over time. Note the 35 year period from 1915 to 1950, where slopes remained above zero. The values generally increased until 1945, and then in the next five years declined until they went negative. Our current period of positive 180-month slopes started in 1977. We see the peak value of the current stretch of positive slopes in 2007 at this point. If history repeats itself, it would mean that we will see this trend line go negative in 2012. This works on both the 35 year time frame and the last 5-year decline from the peak time frame.
The above chart shows the 240-month slope values over time. We see a period of entirely positive slopes from 1920-1955 on a 240-month basis. Our current period of positive slopes started in 1979. If the 35-year period is repeated, we would see negative 240-month slopes in 2014. However, the current period's magnitude has remained at its highest level for a longer stretch than the previous cycle. Before, it took 9 years from the peak before we saw negative slopes. The current period seems to be lagging that.
Since people seem to gravitate towards the 30-year trends for some reason, here is the chart showing the current linear trend for the last 30 year period.
The 30-year slope values have declined over the last (almost) four years, as shown above. It's had its phases, but the overall trend is down in the most recent years from a peak value of just above 0.15.
Here is a chart of the 30-year slope values over time. Most of the time since 1926 has been in positive territory. We saw an extended period from 1926 to 1963 with positive slopes. The peak occurred in 1946, so it took 17 years after the peak to see (slightly) negative 30-year trend lines. In the current period, the positive slopes began in 1974. The peak was reached in 2005 at this point, so it's about the same length of time as the previous cycle. So, we shouldn't expect to see a negative trend line for the 30-year period for another 13-15 years. If this would occur, it would require continued cooling period into at least the early 1920s.
All statements above with regard to putting dates to slope values is simply conjecture based on simple observation of the similar previous cycles in the early 20th century. It is not a prediction.