Well, it’s been quite some time since I have taken a look at the charts and graphs and data on temperature trends. I’ve downloaded our good friend, the HadCrut data set and tried to remember all the spreadsheet manipulations I used to do back in the good old days…
In the interest of time and brevity on a per day basis, I plan on submitting a few separate posts to take a closer look at the charts rather than trying to do a big mega-post.
Today’s submission is just the overall total trend, and the current longest period length of time backwards from current that demonstrates a flat or cooling trend in the data.
It’s been quite a while since I’ve provided an update, and in that time there has been a stretch of warmer readings year over year that spanned a fairly long part of that period. From July 2008 through July 2010, the temperature anomaly compared to the previous year’s anomaly of the same month increased in all but 3 of those months. This can’t be entirely explained by an ESNO event, though the second year of that period does correspond with positive readings in the ENSO index. In each of the last 9 months, the year over year anomalies have been lower, and this does seem to correlate with negative ENSO readings starting 12 months ago.
I’ll take a look at the 60-month through 360-month trends in future posts. For now, I present the overall trend line (which I’ll remind readers to take note of the sine-wave type cycles within the linear trend, which I’ve demonstrated relates to PDO and AMO indices in large part). While a straight linear trend is clearly not entirely explanatory due to cycles around the line, it does seem to do a pretty good job of showing the underlying long-term trend. The more severe upward trend seen in the last 30-40 years is, simply looking at the data, consistent with a cyclical phenomenon. So, there is a linear warming over the last 160 years with intermittent periods of increases and declines. The slope value in the line represents the uynderlying rate of warming per month, which is 0.0373. This is a monthly average change in the anomaly, with the anomaly stated in terms of 0.01 degrees Celsius. Multiplying this by 12 to get the average linear annual change tells us that global average temperatures have increased 0.0045 degrees per year. [Here is where I put in the caveat that I’m just explaining the results of the given data set. To the extent that there is error and assumption in the data, this may or may not have a basis in reality]. Multiplying the annual rate by 100, we see that the average temperature is increasing by 0.45 degrees Celsius per 100 years. Despite the more recent decades of increased pace, there isn’t an immediate compelling reason to believe it’s not cyclical in nature. The last 15 years or so look similar to the period that started in the early 1940s. I don’t think it’s a coincidence that the AMO and PDO cycles appear to have about a 60 year cycle period, which is something I showed in some older posts.
The other chart I’ve updated and am presenting here is the latest period of flat or cooling temperature anomalies. This is just using the latest month as an endpoint and seeing how far back we can draw a line where we can demonstrate straight from the data that temperature has not increased during that period. By implication, we must understand that drawing the line back to any prior point will show that there is a positive slope to average temperature. So, this is not attempting to demonstrate that temperatures have not increased at all over time, just that there has not been warming for some period of time. The period we can go back to under this measure is August, 2000. NOTE: I missed a reversal back to negative spanning a longer time period. The actual longest current trend period that is negative spans back 14 years. My apologies for the oversight. Since the last data point here is April, 2011 that means there has been no warming in overall global temperatures for the last 10 years, 9 months.
Looking at the chart, you can see the 2-year increase in year over year temperature anomalies in context to prior temps. The trough occurred in early 2008, and the increase in anomalies over the next two years reached levels that peaked at a lower level than two other prior peaks in the 11 year period. In those spikes the anomaly hit 60, whereas the peak anomaly a few months ago fell short of that level. So, overall, anomalies are flat from a trending standpoint at a level of just above 40. Chart below: