It is advisable to refer to climate scientists, if you want to make up your mind about climate change related issues. This sounds pretty straight-forward, but were it simple, I wouldn't be writing this blog. Nobody disagrees with the notion that asking climate experts for advice on climate change is a good idea. But in contrast, there are large disagreements on (i) who these experts actually are (and who is most definitely not), (ii) whether they themselves have hidden agendas, (iii) whether there is a consensus on what they are saying, and many more. You see, we will not come to a conclusion easily.

First of all: Define the question you aim to ask

So let's keep it simple by focusing on the main question of climate science, which is most probably: "Are humans responsible for the current changes in our climate?". Several years ago, the question "Is climate change even real?" may still have been a contender for being the main question. But while e.g. Donald Trump still claimed in 2012 that global warming was a hoax by the Chinese government, even he now acknowledges the reality of climate change. However, the question of the cause of climate change is a different one. Donald Trump now believes - like many others - that climate changeis occurring naturally and humans are not responsible for it. The number of people that are flat out denying that climate change is happening is dwindling and maybe already comparable to the amount offlat-earthers. People that once denied climate change as a whole, now shifted their stance to denying that humans are its cause. Thus, we can settle for "Are humans responsible for changing our climate?" as the main question of climate science.

How can we ask for the opinions of climate scientists?

Equipped with this question we now want to ask climate scientists, what their opinion on the matter is. Alas, there is no area of science called "Climate Change Cause Evaluation", so what we could do instead is refer to all climate scientists, no matter if they drill for ice cores, analyse satellite data, or build climate models. Firstly, we need to identify these people. This is pretty simple, because climate scientists publish their scientific findings in science journals, which can be accessed often publicly or over academic university servers. Now that we have obtained a list of scientists that published climate science, we can read their publications to see whether they have included statements on whether humans are the cause of climate change. Alas, only a comparably small number of scientists will write something like that in their publications because it is simply off-topic. They are writing about their satellite data, about melting glaciers, about computer predictions, or ice cores. Also including a statement on the cause of climate change would be like adding a statement that the earth is not flat or that it revolves around the sun. Scientific publications have to be concise and precise, they often have word limitations, and there is not much room for stating the obvious. And spoiler alert: Humans causing climate change is common knowledge and settled science for climate scientists - they do not see a point in stating it in all their publications. But back to the topic: If they do not declare a statement on the cause of climate change in their publications explicitly, we will have to ask them directly, e.g. via their email addresses, which are just as publicly available as most of their publications. Not all of them might respond to such an email, because there is just not the time to answer all surveys circling their ways through the science-sphere or elsewhere. But with the statements in the publications plus the email responses there will already be a pattern visible. The aforementioned process has been done in 2013 in order to evaluate if climate scientists think that humans are responsible for climate change. The study by Cook et al. is openly accessible for everyone. And it found that 97% of climate scientists think that humans are the cause for climate change.

Cook et al. were far from the only ones that tried to answer this main question of climate science by examining the mood in the scientific community. There wasOreskes et al. in 2004, Anderegg et al. in 2010,Doran et al. in 2011,Verheggen et al. in 2014,Stenhouse et al. in 2014, andCarlton et al. in 2015. They all tried to find out what climate scientists think about climate change and they employed different strategies on finding a response. All of them found a consensus of between 90% and 100% of experts agreeing with man-made climate change. Furthermore, they found that the higher the expertise of the respondents was, the higher was the consensus. As a matter of fact, these studies are even summarised in a meta-study on its own, a study on the consensus of the consensus studies, published byCook et al. in 2016. The amount of openly available publications on this matter in combination with the found results makes us see that there seems to be a pretty strong consensus on man-made climate change. A morerecent article from the Guardian (July, 2019) sheds some light on the current situation, which may be an easier read for everyone who does not feel the need to struggle through the scientific studies and who wants to have a more recent but still reliable evaluation of the topic.

Expert consensus results on the question of human-caused global warming among the previous studies published by the co-authors of Cook et al. (2016). Illustration: John Cook.

What do these numbers even mean? Is 97% a lot?

Climate science deniers enjoy pointing out that unless we are 100% certain of the cause of climate change, we should not act against it. That means not only making completely unrealistic demands, but also negating the magnitude of consensus we are talking about. Imagine your child is sick and you are going to 100 doctors for diagnosing the cause. 97 of them tell you they are sure about the sickness, its cause, and they propose possible treatments. Only three out of the 100 doctors are saying that probably everything will just work out fine anyway or that you cannot do anything against it or that your child is not sick at all. Would you listen to the three or to the 97 doctors? The answer seems obvious.

Now that we have an impression on what the actual experts on climate science are thinking, we could be glad and go home. Now that the experts have spoken, we could start taking measures against climate change by introducing policies that target climate violating behaviours (like burning fossil fuels). But there are people and institutions at work to prevent this from happening. They deny man-made climate change, they discredit climate scientists, and they doubt the consensus studies. By doing this in an orchestrated manner, they sow confusion in the public. They willingly spread misinformation and try to deconstruct the works of climate scientists. Who are these people, what is their agenda and how do they work? These questions and more will be addressed in my blog post #03.