First published on LinkedIn, 28.07.2015
I am following the ongoing discussion between climate change advocates and skeptics since my studies in geophysics and meteorology at the University of Hamburg where one of the advocate group is located. I will not point fingers to one side or the other because both sides provide useful insights to solve the question whether anthropogenic climate change is real or not.
But since my study years the discussions grew from scientific disputes to religious-like beliefs and the discussions have reached a level of personal opinions rather than facts.
Let me illustrate this on a recently published dispute between Marotzke and Forster  as climate change advocates and Nicholas Lewis as climate change skeptic . It contains three reasons for the controversy around climate change. But I start with a fundamental issue, which is only implicit part of the Dispute.
- Probable flaw in the main assumption
Correct modelling of the past don’t necessarily mean that the same model yields correct future predictions. Geological processes like plate tectonics, mountain building (orogeny) and meteorological processes like the water (hydrological) cycle happen in the same manner since the beginning of the earth until now and therefore we can predict future behavior by understanding the past. But the Earth‘s climate is a different category. It is known as a chaotic process which means that small changes in one parameter can cause large effects in the result (e.g. butterfly effect). In fact, some of the most popular chaotic figures, the Lorenz attractor, was discovered by Edward N. Lorenz a meteorologist by analyzing meteorological data and the underlying mathematics. He claims in his paper  that: “If the [weather] system is stable, its future development will then remain arbitrarily close to its past history, and will be quasi-periodic. …since the atmosphere has not been observed to be periodic…..no forecasting scheme could have given correct result…” In addition to the usual chaotic behavior one large (VEI >= 5; ) volcanic eruption will make all existing anthropogenic climate change forecasts obsolete for decades: And in the past 25 years there were 2 eruptions with VEI >= 5; .
- Simulation driven approach
Most of the anthropogenic climate change forecasts are model based rather than data driven and are built from a positive assumption. I will not go into the mathematics, but I have to show one equation to make my point. The following equation is the main subject of the discussion between Marotzke&Foster and Lewis where an energy balance is described as: ΔT = ΔF / (α + κ) + ε. Don’t worry, it is not necessary to understand the equation in detail. You just need to know that three of the four quantities ΔF, α, κ are parameters modelled from simulations and used to simulate ΔT due to lack of direct measurements. You can see from the quantities‘ names that they have no direct relation to known physical quantities: ΔF = change of effective radiative forcing, α = climate feedback parameter, κ = ratio of change in the heat uptake of a climate system. They are hypothetical constructs. The fourth quantity ε is a computer generated random value.
In short: they use simulation results to simulate something that cannot be measured directly. I am not saying you can’t do such thing, but it becomes more and more difficult to understand the reliability of the results, especially if at least one simulation is nonlinear or even chaotic. It doesn’t help to claim that the prediction is correct because 114 simulations based on the same model / assumptions provide the same results . This is comparable to: 114 translations of Grimm’s fairy tales are similar, so the story must be true.
- Opinion and agendas before facts
Science has nothing to do with opinions and agendas. But we scientists, as social beings, have something to do with it and we have to work with that every day. Unfortunately, some scientists become believers of their own opinion instead to discuss issues in a constructive scientific way.
Marotzke is already convinced that the climate change is anthropogenic and he said : “Sceptics who still doubt anthropogenic climate change have now been stripped of one of their last-ditch arguments”. This is an opinion not a fact!
Due to the nature of climate change the chosen approach is an inductive projection which means we don’t know exactly the mechanism behind climate change. We can’t even be sure that anthropogenic climate change exists. Measuring a temperature increase in the last hundred years and a change of our daily weather behavior compared to the last century hasn’t necessary something to do with an increase of CO2 or that it is manmade. There are other explanations that are equally probable. Maybe we have lived in a lucky period where the climate was quasi periodic and this starts to change now, independent of what we are doing?
- Missing constructive discussions
The concept of science is to find reliable and reproducible descriptions of observations we make. In other words: Is there something we don’t understand we try to find a scientific explanation. Due to our human nature we get sometimes lost in our hypothesis. Therefore we should embrace questions which contradict our hypothesis and should discuss them constructively.
Unfortunately, the opposite is quite often the case. I think Lewis provided a good mathematical explanation why the results from Marotzke and Forster don’t work. But he finished his analysis with following sentences: “The statistical methods used in the paper are so bad as to merit use in a class on how not to do applied statistics.” and “All this paper demonstrates is that climate scientists should take some basic courses in statistics and Nature should get some competent referees.” Writing these statements doesn’t help to convince the other side. But this shows how overheated the discussion already is and that the sceptics feel not been taken seriously.
Unfortunately, Marotzke and Forster are not taking Lewis analysis serious. They basically repeat in their answer what they already have published in Nature . And the main reason for why Lewis wrote his analysis was rejected with following statement: “It has been alleged that in  we applied circular logic. This allegation is incorrect.” This shows the narrow-mindedness and arrogance of the advocates of climate change. To have the majority doesn’t mean they own the truth.
In order to solve the climate change issue advocates and sceptics should work together as equal partners in the same group or directly within the IPCC. Only if both sides are satisfied with the results we might be getting closer to the truth.
 Jochem Marotzke & Piers M. Forster. Forcing, feedback and internal variability in global temperature trends. Nature, 517, 565–570 (2015)