May 20 2013

Consensus on Climate Change

A recent review finds that over 97% of scientists believe that human activity is contributing to climate change. That is a very solid consensus of scientific opinion.

This, of course, does not mean that the consensus must be correct, but (along with other data) it makes it unreasonable to claim that there is no consensus, or that there is significant scientific controversy on this topic. In fact, the 97% figure exactly matches prior surveys. Many scientific organizations have also officially endorsed this consensus.

One of the common methods of deniers is to pretend as if there is a raging scientific controversy when in fact there is a solid consensus. Creationists, for example are constantly trying to portray evolution as a “theory in crisis,” when in fact it is doing quite well, thank you.

The study employed an interesting methods. They reviewed 12,000 peer-reviewed published papers on topics relevant to climate change. They then tabulated, for those papers in which the researchers expressed a clear opinion about climate change, whether or not they supported the conclusion of anthropogenic global warming. In over 97% of cases they did.

From the abstract:

We analyze the evolution of the scientific consensus on anthropogenic global warming (AGW) in the peer-reviewed scientific literature, examining 11 944 climate abstracts from 1991–2011 matching the topics ‘global climate change’ or ‘global warming’. We find that 66.4% of abstracts expressed no position on AGW, 32.6% endorsed AGW, 0.7% rejected AGW and 0.3% were uncertain about the cause of global warming. Among abstracts expressing a position on AGW, 97.1% endorsed the consensus position that humans are causing global warming.

No survey is ever perfect – whenever you evaluate a subset of people in order to draw conclusions about the larger group, there is the possibility of selection bias. In this case one might argue that scientists who reject anthropogenic global warming are less likely to express those views in a peer-reviewed paper, or to have such views published.

This method, however, is reasonable. They also backed this up with another phase of the study in which they invited authors to rate their own research and opinions, and 97.2% endorsed the consensus of global warming. While it’s possible to quibble about this number, given the strong agreements among various methods around the 97% figure, it’s difficult to argue that the true figure is significantly different.

Why do we care about the consensus? Isn’t this just an argument from authority? Well, yes and no.

It seems reasonable, especially for those who consider themselves skeptics, to argue that facts and logic should determine a scientific question, not authority. Or that we should “let the facts speak for themselves.”

Unfortunately, facts cannot speak for themselves. Scientific evidence needs to be examined, rated for quality, interpreted, and put into a broader context. There is often no simple connect from facts to conclusions in science – background knowledge, knowledge of the processes of science, familiarity with critical thinking, logical pitfalls, and the effects of bias on interpretation are all necessary to come to a reliable conclusion about what those facts are telling us.

Different individuals are likely to have different biases and knowledge bases, and therefore may come to different conclusions about the same set of data. No individual, therefore, can be the ultimate authority on any scientific question.

The power of consensus is that individual quirks and biases will tend to average out. The consensus of scientific opinion, therefore, is a way to gauge the agreement and power of the scientific evidence.

The only other alternative is to evaluate all the scientific evidence first hand and come to your own conclusion. The potential pitfall here, however, is that individuals who are not experts in the relevant field believe that they can do this by examining secondary sources, such as popular writings on the topic. This is naive, however.

In order to really understand the evidence base for any scientific question you need to be able to read the technical literature first hand, and have a reasonable working knowledge of this literature. You then need to challenge your understanding of the evidence by discussing it with other experts, who may be familiar with evidence you missed, or have a perspective you do not. In other words – you have to engage intimately and extensively with the evidence and with the community.

In order to do this you pretty much have to be a full-time scientist focusing on the relevant area of study.

It seems absurd, when you really look at it, to substitute your own opinion based upon reading a smattering of simplified popular writings for that of the consensus of scientific experts who live and breathe the science.

What typically happens is that individuals who reject the consensus often come to the conclusion that science itself is broken. They reject science and the institutions of science, in order to justify their rejection of the particular consensus on which they disagree. Scientists, they believe, are therefore closed-minded, corrupt, or mindlessly follow the herd.

This is little more than ad-hoc special pleading, however (they are just making it up). Anyone who works with actual scientists would find such statements to be hopelessly out of sync with reality. Sure, there are individual scientists who are corrupt or closed-minded, but most vigorously defend their own intellectual independence.


For the average person (someone who is not a working expert in a particular field) the consensus of scientific opinion must be taken very seriously, and should not be casually tossed aside. In grappling with any scientific question, you should first try to understand what the scientific consensus is, how confident are scientists, is there any significant and viable minority view, and why scientists have come to that conclusion.

Humility and reason dictate that the consensus view should be given appropriate respect. I am not discouraging anyone from trying to understand the evidence first hand, in fact I recommend it. Learn and understand the primary evidence as much as your interest, time, and ability take you. Just be extremely cautious before you believe your opinions trump those of hundreds or thousands of working scientists.

With respect to anthropogenic global warming, there is a solid and confident consensus. You should be especially cautious of rejecting this consensus because it does not agree with your political world view.

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