But one has to ask, Why confine results to 1970-2011 (the terminus ad quem for the study, published in 2012, was 2011) when you can easily go back to 1895 and get a per decade trend result for a much larger sample?
The change in average temperature on a per decade basis for the whole available sample period 1895-2014 produces 0.2 degrees F per decade in Michigan, three times less per decade than for 1970-2011 alone. The result is identical also through 2011. Despite the significant warming since the year 2000, the long term trend remains unmoved and the current period of warming may actually have run out of gas.
I thought it would be interesting to use the length of the sample period in question (42 years) and go back to the beginning of the record in 1898 and look at each 42 year period from then going forward to 1973 (which takes you through 2014) to see if there are any periods of decadal warming trend comparable to +0.6 degrees F per decade in 1970-2011. I chose 1898 to avoid some gaps in the record in some places in prior years in Michigan.
The results are graphed below.
It turns out there are five 42-year periods showing temperature trend of +0.5 degrees F per decade on the left side of the graph, beginning in 1903, 1912, 1914, 1915 and 1916. (Students of the Dust Bowl beginning in 1930, take note, as also those studying economics. Weak GDP of the era may be associated with warmer climate, as it also seems to be now.)
These correspond to six 42-year periods showing temperature trend of +0.5 degrees F per decade on the right side of the graph, beginning in 1960, 1961, 1962, 1963, 1964 and 1973.
If that were all that were to it, there would be no discussion of global warming today, despite the consecutive nature of the recent examples. The two data sets are almost a wash.
What is remarkable about the more recent data is the presence of four 42-year periods of +0.6 degrees F decadal trend (beginning in 1967, 1968, 1969 and 1970), and four of +0.7 degrees F (beginning in 1965, 1966, 1971 and 1972), all in conjunction with the +0.5 degrees F periods. It's a trifecta of warming data.
Still, overall the results show that there are two distinct periods where the decadal trend is consistently +0.2 degrees F or above: the 27 years from 1898 to 1924, and the 20 years from 1954 to 1973. In the former the average of the decadal uptrend is +0.3555 degrees F per decade. In the latter the average of the decadal uptrend is +0.4950 degrees F per decade. Clearly the latter period, contemporary with us, is significantly warmer than the former, by 39%, about which some of us have become hysterical.
The antidote to this is the trough of downtrend years in the middle of the graph which coincides with the period of the global cooling hysteria of the late 1960s and 1970s. The 42-year trend record went negative for 1928-1969 and stayed negative to flat until the period 1946-1987, nineteen years straight, twenty if you count the flat period 1927-1968. Year after year, the 42-year trends ended -.1 degrees F decadal trend or -.2. Many climate scientists predicted the return of an ice age while unbeknowst to them the seeds of a warming era were already germinating.
The record shows how quickly things can turn, for example 0.5 degrees F in trend in just seven years from 1923 to 1930, from above trend on net to well below it.
The decadal trend fell by a whopping 50% between 1917-1958 and 1918-1959, from +0.4 degrees F to +0.2.
More recently the decadal trend fell by 28.5% between 1972-2013 and 1973-2014, from +0.7 degrees F to +0.5. (It's entirely within the realm of possibility that decadal trend could revert to normal by the close of 2017.)
There was just one similar abrupt change to the upside. Between 1964-2005 and 1965-2006 the decadal trend shot up 40% from +0.5 degrees F to +0.7.
Otherwise the record shows incremental change in the trend from year to year, 0.1 degree F up or down at the most.
Don't be surprised when you see it.
