VACATION ALERT: I will not be posting for the next couple of weeks. The family and I are driving cross-country in a big honkin’ white Cargo Van. We are going to Delaware. “Why Delaware”" you may ask. It’s a valid question. I won’t get into all the details, but let’s just say that we choose our vacation destinations by drawing them out of a hat, under the theory that every place has something to offer. That theory is about to be tested… Anyway, just wanted to let you know of the upcoming hiatus.
On to temperatures…
GISS is always an interesting data set to review, because you’re never quite sure what you’re going to get. In a world where people like consensus, it is somewhat striking to me that we have general agreement between the RSS and UAH, and even the HadCrut data sets, and whenever there is an outlier it’s likely to be the GISS data set. Yet, when people quote statistics on global temperature, the GISS is the preferred set. This, despite numerous documented algorithmic data adjustments that have, over time, a non-negligible impact. Also, there is the real question of whether or not the bias of James Hansen enters into the evaluation of the data.
Nonetheless, it’s the reality we deal with that this is data that is looked to for policy decisions. So, if for that reason alone, it is worth keeping an eye on it so we can speak intelligently to what it is telling us.
First, let’s review the most recent data point:
March anomaly = 47 (in terms of .01 degrees Celsius). This was the lowest March anomaly since the year 2000. It was 18 lower than the March 2008 anomaly, but 6 higher than the February 2009 anomaly. This is quite different than UAH, where the movements were reversed.
Streak: This month’s lower year-over-year anomaly broke a streak of 6 consecutive months where the anomaly was higher year-over-year.
Rank: March 2009 ranks as the 11th highest anomaly in the data (since 1880, or 130 anomalies. 8.5 percentile.) Overall it ranks as the 95th highest anomaly in the data set of 1,551 values (6.2 percentile).
Average: The 12 month average ticked down from a recent high last month, and stands at 46.8, which puts it right at the level it was in January.
The period of time where a best-fit line can be drawn that indicates no change in global temperature is not 100 months long. The last time we had a stretch of 100 consecutive months where a negative trend line could be fit was the period beginning April 1988. In recent history, during the stretch of time for which we consider the warming to be measurable, the longest stretch where a horizontal/slightly negative trend line occurs is from January 1987 through April 1997. That spans 10 years and 4 months. If our current front anchor remains at December 2000 as a starting point, we will not reach that until March 2011 – 2 years from now. So we still have a ways to go to declare that this is beyond any previous hiatus in temperature rise during a potentially warming period. It could be less time than that if some cooler temperatures are forthcoming, driving our starting point back in time a bit. Supposing we would reach that point, the previous time a flat or negative trend line of that stretch occurred is the period beginning June 1969. At this point, it seems get pretty iffy whether or not the trend line can be explained away. But we’re not at that point quite yet.
Here are some notes on the different trend periods:
60-month: Current slope = -0.1123 (-1.35 degrees Celsius cooling per Century). Kind of hovering around the same level as the last four months (ranged from -0.1086 to -0.1151). Here is the comparison to its peak slope, period ending May 2007.
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