It was quite hectic in the last month. Now the dust is slowly starting to settle, I will try to pick up blogging again. The subject of previous post was the statement that climate scientists are as certain about climate risks as oncologists on cancer risks that come with smoking. I ended that post being confused whether the authors meant that the evidence of climate risks is as strong as the evidence of the link between smoking and cancer or that there is the same “overwhelming” consensus as the medical scientists have on the link between smoking and cancer.
Scientific American seems to suggest the former, the scientific paper that was linked to in Scientific American the latter. This post will explore the case that they meant that the “evidence of climate risk is as strong as the link between smoking and cancer”, so this post will be about the evidence of the cancer risks linked to smoking and whether the evidence of climate risks is in the same ballpark.
Before I look into this, I can somehow understand the comparison between medical science and the climate science. Both study a very complex system. Medical sciences study the human body and climate scientists study the Earth with its climate system. The complexity of the human body and its interactions means that there is not one conclusive proof, but there are multiple lines of evidence. We hear the same thing about climate science.
So far, so good.
Let’s first look at the link between smoking and cancer risks. As far as I can see, the Scientific American article is about the direct link smoking/cancer, not about second hand smoke, so I will look into the direct link between smoking / cancer.
In medical sciences, the link between smoking and cancer is established by multiple lines of evidence. The article The history of the discovery of the cigarette-lung cancer link is the clearest and most extensive (though somewhat biased) that I came across, so I will take that as a guideline for this post. These lines of evidence are:
- Population studies
Were already held since the end of the 1930s and suggested that there was a link between smoking and developing cancer. Huge numbers of people, smokers and non-smokers, were followed in such studies. One of those studies had for example 187,766 participants. Investigators noticed a parallel rise in cigarette consumption and lung cancer.
- Animal experimentation
Even earlier than the population studies, it was shown that tobacco extract could induce cancer when it was applied on the skin of laboratory animals. Later, it was shown that cigarette smoke tars had the same effect.
The paper seems to suggest that animal experimentation unequivocally showed the link between smoke and cancer. This is not exactly true in reality. Smoke inhalation tests showed no or little effects in laboratory animals. My guess is that this is because the shorter lifespan of those animals. A laboratory mice lives about 2 years, a rat a bit longer, but exposure to smoke in humans is sometimes many decades before tumors develop. This is probably one of the reasons why the tobacco industry was able to resist the link between smoking and cancer for so long.
- Cellular pathology
On cellular level, it was already known from the 1940s that cigarette smoke could cause ciliastasis (the damage of the hair-like structures that are responsible for removal of contaminants that got in the lungs) and that tumors formed where these cilias were affected.
- Chemicals in cigarette smoke
Chemical analysis showed that cigarette smoke and tar contained many carcinogenic substances.
Although none of those lines of evidence is really conclusive, it is not unreasonable to come to the conclusion from all these lines of evidence that smokers have a higher risk for developing cancers. Population studies suggest that smokers develop more cancers than other groups. This is also confirmed by animal models and by medical knowledge on cellular level. It is also known that cigarette smoke contains many carcinogenic substances and that the structures that have the function to remove such substances from the lungs are damaged. Meaning a longer exposure time to those carcinogenic substances.
To me, that seems a strong indication of the link between smoking and cancer.
How does this compare to climate risks?
A first problem that we encounter is the subject of study: 1 (ONE) patient (Earth and its climate system). Unlike medical sciences that have investigated MILLIONS of people to unravel that link between cancer risks and smoking.
It is not really sure whether the climate system is actually a “patient”. We started reliably measuring many variables of the climate system only AFTER the alleged illness became visible. It is far from sure what the normal natural variation of the climate is. Unlike medical sciences that studied healthy as well as ill individuals for a very long time. They know how a person with healthy lungs looks like and distinguish them from those with lung cancer.
Climate science is a relatively young science and only gathered a limited amount of data. Although climate sciences study the long-term climate, there is little reliable historical data available. The reasons for the historical (surface) measurements were not climate related. Temperatures were measured for local weather prediction and the interpretation of those measurements towards climate are riddled with issues like changes of equipment, changes of location, changes of methodology, uneven spatial coverage, convenient bias, recording of non-climate related changes (like UHI effects) or other human influences (like man-made structures that produce/accumulate heat or non-standard locations) and so on. Climate scientists seem to struggle how to estimate the global temperature, let alone the global temperature of say the 1940s and the records keep on changing.
Performing experiments is not really possible in a population of 1. There is no second Earth to experiment with to see what happens when we add or extract CO2 from its atmosphere. In fact, this is the first time we are in this situation with 400 ppm (and rising), so we have no practical experience how it will pan out in the short-term or the long-term. There are of course theories that tell what could happen when atmospheric levels exceeds 400 ppm. This void is filled in by means mathematical models, which might be useful, but not necessarily for predicting what will be the climate in say 100 years.
Unlike medical sciences that have trial & error experiences and animal experimentation over an extensive period of time.
There are of course all kind of laboratory tests on one/a few particular elements of the climate system. They could be measured very correctly, but the problem is that the results have to be linked back to the complex, coupled, chaotic climate system and then it becomes a lot less clear. The physical properties of CO2 are well-known, but the atmosphere and the Earth contain many other variables that could influence the outcome. There is no doubt that CO2 has a warming effect (that has been know for over a century by now), but in the atmosphere there are many other elements and processes at play that could enhance or balance that effect.
However, it could be entirely possible that the authors of the LiveScience article and those of the Scientific American article did’t mean that “the evidence of climate risk” is on par with “the evidence on the smoke/cancer risk”, but that “the consensus on climate risks” among climate scientists is as high as “the consensus on the link between smoking and cancer” among medical scientists. I can imagine that there is at least a 97% consensus on the link between cancer and smoking in medical sciences, if not higher. They have the data to show for it. The latter consensus is built on a tremendous amount of expertise of the healthy system as well as the unbalanced system as well as the treatments on basis of the gained knowledge. Something climate science lacks at the moment.
Concluding, I am not believing for a moment that climate scientists know as much about climate risks as medical sciences about cancer risk. By any measure, the strength of the evidence on climate risk is but a bleak copy of that of the cancer risk in medical sciences. Neither do I believe that the climate risk consensus is as well-established as the cancer risk consensus.
via Trust, yet verify
July 31, 2017 at 04:18PM