By Ingemar Nordin
There was quite a stir when the Norwegian Statistics centre published a paper by John K. Dagsvik and Sigmund H. Moen. The paper has the title “To what extent are temperature levels changing due to greenhouse gas emissions?” It was also noticed abroad:
Source: Wall Street Journal
The paper goes through the models by IPCC and compares them to empirical data. And they put them to test against proper statistical models. Here is from the abstract of the paper:
“Weather and temperatures vary in ways that are difficult to explain and predict precisely. In this article we review data on temperature variations in the past as well possible reasons for these variations. Subsequently, we review key properties of global climate models and statistical analyses conducted by others on the ability of the global climate models to track historical temperatures. These tests show that standard climate models are rejected by time series data on global temperatures. Finally, we update and extend previous statistical analysis of temperature data (Dagsvik et al., 2020). Using theoretical arguments and statistical tests we find, as in Dagsvik et al. (2020), that the effect of man-made CO2 emissions does not appear to be strong enough to cause systematic changes in the temperature fluctuations during the last 200 years.” (my emphasis)
According to this study there is no possibility to distinguish between natural variability and anthropogenic influence from CO2. None of the IPCC models are sufficient for proving such a causal link.
Still, the IPCC, the UN, most of the media and most politicians take such a link for certain.
When this study was first presented in 2015 to the Norwegian Statistics, it was refused. The result was simply too provocative. But no one has proved it wrong or pointed out any faults in the statistics. Dagsvik is one of the most prominent statisticians in the world. And this time, September 2023, it was accepted.
Judging from the Norwegian news articles about this it seems that the criticism misses the point of the paper. They believe that Dagsvik et.al. claim that there has been no global warming. But what they say is that, from a statistical and historical point of view, it is not possible to distinguish this warming from natural variations.
For most of us that are familiar with climate history this comes as no surprise. We know that climate has changed in history, often with bigger and faster changes than now. And on a global scale. Of course, this does not disprove the possibility that CO2 is playing a role for modern warming, it only points out the fact that we cannot distinguish between that possibility and natural variations.
There is one more point mentioned in the abstract cited above. The authors tested the existing climate models to see whether they were able to track historical temperatures. According to the authors these models failed to do that. This is remarkable since the data they use comes from official data bases. There are numerous reconstructed series of temperatures – from sediments from lakes, from ice cores, from tree rings and from direct observations around the world – which they discuss. But modern climate models replication of historical temperature series are not very good.
The discussions of both the data series and the tests of various models may be of interest to the specialists. But it seems clear that this comparison, and failure to replicate the climate past, is a BIG problem to the IPCC scientists. Either they will have to demolish existing temperature reconstructions of historical temperatures, or they will have to demolish their own climate models and start all over again. Without such a deep-going modification there is no basis for trusting the IPCC model predictions of future climate. We simply do not know how much, if any, the greenhouse gases affect temperatures.