(click to enlarge)
When one presents a chart showing that there has been no global warming for the past 12 years, one can expect that the AGW alarmists will be . . . well, alarmed. As a result, we can expect that the total arsenal of "you can't believe your lying eyes" type of rationalizations will be brought forth in an effort to show that it doesn't matter what the data says. Their arguments fall into two types, and so I will try to deal with them here.
The first argument claims that the starting point for the data has been cherry picked, and therefore proves nothing. Let me mention at this point that last year the argument was also used that the end point was cherry picked because the data ended in a La Nina. This year the data ends in an El Nino, and the trend is still flat. So that argument has been disposed of by time.
The alarmists objection typically asks why an earlier or later starting point was not used. I think that we have to answer that question in respect to the question that we are trying to answer in producing such a chart. The question that I want to answer is "how long has the global temperature trend been flat". If I choose a date before 1998 I am not answering that question. I know already that the temperature was rising before 1998. I am not trying to debate that point. And I know that if I use data from before 1998 that I will get a positive slope. But I'm not making the statement that temperature has been flat for 15 years or 20 years. I'm making the statement that it has been flat for 12 years.
Then the question is asked, "why did you start with an El Nino year and not with 1999 or 2000". This is actually a relevant question, because 1998 was strongly effected by an El Nino that would serve to lower the slope of the trend. In other words, if I cut off 1998, my trend goes positive. But what all of the alarmists choose to ignore is that there were 8 ENSO events in that 12 year time period (5 El Ninos and 3 La Ninas) and that one has to consider them all to decide if the flat trend is actually just and ENSO artifact. So while the 1998 El Nino exercises a strong influence on the slope, one can't simply overlook the fact that the 98 El Nino was followed, only 3 month later, by a La Nina that lasted over two years. The effect of those two events at the beginning of the chart on the slope of the trend basically cancels out. I show how the ENSO events effect the slope here.
But, all things considered we should be able to answer all of the ENSO related starting point issues by simply using an ENSO corrected chart. Last year, Gavin Schmidt, from Real Climate, produced such an ENSO corrected product for the HadCrut3 global data set. I plotted the data here:
The profound effect of the ENSO correction can be seen at the beginning of the chart where the 98 El Nino is brought way down. But as the chart shows, with corrections for all ENSO events accounted for, the remaining trend was still basically flat. Furthermore, the difference between the trend lines for the ENSO corrected data and the non corrected data is tiny. The ENSO corrected chart should put to rest any arguments that the starting point is cherry picked to gain the benefit of a powerful ENSO year. But you can bet that the alarmist will still try to find a way to support that misconception.
The second part of the argument that alarmists present against this kind of chart is that it is not statistically significant. In other words, we cannot say that the trend lines shown in the chart represent the true trend with 95% certainty. This argument is a straw man for more than one reason. We are not trying to present the new trend line as being the new trend with 95% certainty. We are simply saying that there has been no warming for the past 12 years. The argument against such a short period of time is that the variability around the trend is too large to give the trend meaning. That is fine as an argument if you don't look at the physical reasons behind the argument. Climate has large elements of variability over the shorter time period. These are things like ENSO, PDO, AMO, solar, volcanoes, aerosols, etc. But we know what all of these things are, and we can investigate how they effect our chart using things like the ENSO corrected data that I used above. By the way, that correction removed much of the variability, thereby shortening the time period needed for significance. The problem with the current 12 year flat trend is that it cannot be explained by natural elements of variability. I have asked the alarmists, like Gavin Schmidt, many time, to explain the elements of natural variability that were overriding the CO2 signal. But they have no answer.
This means that the answer is one of two things. Either the forcing expected from CO2 is too large, or there are elements of natural variation that are very strong and that are not accounted for by current climate knowledge. If the later is true, then those elements of variation are also not accounted for in the models.