Global Warming Minute – Why is the IPCC “95% Certain” that Climate Change is Manmade?

09/30/20132 Comments

In recent days, you’ve probably heard ad nauseum that the UN’s new IPCC report claims that it is “95% certain” that humans are causing climate change.

95% is a very specific number. So where does it come from?

The IPCC uses a “likelihood scale” that assigns percentages to various phrases, ranging from “exceptionally unlikely” (0-1% probability) to “virtually certain” (99-100% probability). This sounds like it is based on a precise scientific measurement or well-defined statistical process, but when it comes to deciding how likely it is that climate change is manmade, this is in fact a subjective decision that is made by the report’s authors.

According to the IPCC: “The approaches used in detection and attribution research […] cannot fully account for all uncertainties, and thus ultimately expert judgment is required to give a calibrated assessment of whether a specific cause is responsible for a given climate change.”

In other words, the “95% probability” that is making all of the headlines is nothing more than an arbitrary number decided on in closed door meetings between the report authors. Still, it serves an important propaganda purpose in giving a veneer of scientific credibility to the decision, one that a media that never bothers to explain these decisions to you thinks you will be too stupid to figure out for yourself:

So how reliable is the IPCC process in general? That will be the subject of next week’s report.


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  1. The below video on the topic of global warming is one of the best I’ve ever seen on the subject. They propose that while ‘global warming’ is a falsified pseudo-scientific hoax, climate change is still very real and that pollution, generally speaking, is harmful and dangerous to the planet. I think most of us can agree that this is a perfectly reasonable stance to take when we look at all the evidence available to us.

  2. stoneyv says:

    The choice of 95% certainty is related to confidence intervals in statistics. A 95% confidence level is used most of the time. I will not be able to explain all of this here and a sense of curiosity and patience will be needed to understand this concept. Though, a really great way to be introduced to these concepts is to watch the excellent videos from the Khan Academy on youtube.
    I was also surprised to see such a straight forward explanation of the confidence interval on Wikipedia.
    Also, Khan Academy also has excellent videos that explain finance and banking. I highly recommed it these :)

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