Guest essay by Barry Wise
Christopher Monckton has pointed out that a trend of zero or smaller can be calculated stretching back over 18 years, but critics have pointed out that this encompasses the super el Niño of 1998 and so biases the trend downward while the overall temperature is still rising. Of course they also don’t mention that the el Niño biases the trend upward when the trend is viewed in it’s entirety. Now Lord Monckton has identified a valid point and so do his critics. What if we look at how the trends vary over differing lengths of time? Can Lord Monckton be validly accused of cherry picking or are his critics nit picking? This article will attempt to show a broader view of how the trends have varied over time, both from the beginning of the the record and from the end.
To begin, at what point do we say that a trend of a given length makes sense in terms of whether it’s an indication of future global temperatures or just a statistical anomaly? Obviously the longer the better, or so one might surmise, but then that’s assuming that the data represents a linear trend. The more data you have the less any additional point will affect the overall trend. Given that, one might expect the trend to oscillate around a given value with a reduced amplitude as it zeroed in on the actual trend.
So what actually happens? For this exercise I’ll use RSS lower troposphere data since that is what Lord Monckton used. Here is the RSS data for the full period of the data from 1979 to the present with the 1998 el Niño shaded in grey and showing the least-squares linear-regression trend line for the entire data set. The el Niño time period is based on data from El Niño and La Niña Years and Intensities. The slope of the line is approximately 1.2 K/century which, as it turns out, is below the low end of the IPCC projection (1.9 to 4.2K/century) but is consistent with a doubling of CO2 with no secondary effects.
Let’s look at how the trend has varied starting from the earliest data. I’ll start with a minimum length of ten years (an arbitrary length but shorter lengths give widely varying trends that make it hard to read the graph) and I’ll increase the length in one month increments. The trends are plotted based on the end date used for the data of each trend, with the full data shown below as a reference. The shaded area brackets the 1998 el Niño so we can see where it enters into the computation of the trends. Notice how much the trends vary prior to the el Niño. Everything from about 1.6 down to .4 K/century. This would indicate that data that is less than 20 years (at a minimum) is unreliable to discern the trend over a longer term. Notice too how the trends peak with the el Niño but immediately start tailing off. By the end of the data the trend is at the 1.2 K/century we calculated before and the change in the trend is flattening out. Also of note is the rapid rise of the trends when the el Niño occurred.
Now let’s look at how the trends changes as we increase the length in one month increments starting at the present and working backwards to see how Lord Monckton’s 18 year 8 month value fits into the changes that occur as we vary the length of the data. In a similar fashion to the previous chart, I started with a minimum data length of ten years. Notice that not only are there negative trends where the el Niño data is included but there are also negative trends prior to that data. Additionally, the trends prior to including the el Niño are even more pronounced, longer and extend back to June 2000 which is over 15 years. Also of note is that this includes the 2010 el Niño which, by it’s relative location, should bias the trends in a positive direction at these lengths. At no point does the trend exceed .5 K/century for the data after the 1998 el Niño. Just prior to the el Niño the trends are approximately .7 K/century.
This article has just been my attempt to show a broader view of how the temperature trends have evolved. I make no claim to whether Lord Monckton or his critics are correct. In summary we now have over 35 years of satellite data with over 15 years post 1998 el Niño showing little, no or even negative trends at that length. The data prior to the el Niño also shows trends that are at or below that the IPCC has promoted, not to mention the entire record. While some have critiqued Lord Monckton’s trend because of the inclusion of the super el Niño I would question their consistency because I haven’t seen a similar complaint based on the much larger effect that it had on the trend from the beginning of the record. Given the lack of a positive trend post el Niño, it would appear that there was a step that occurred in the earth’s atmosphere’s temperature. The present el Niño is being touted as being another massive one. Will it too show a step?