The straplines on major news channels today were referencing a study that said that evidence for man-made ("anthropogenic" is the word they like to use) global warming has hit a "gold standard". That piqued my attention because I hadn't realised there was a gold standard in scientific analysis.

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In a report clearly aimed at arresting further disinformation about climate change - and its causes - through (horror 😱) facts, a team of researchers from the United States, Canada and Scotland said that evidence that human activities are responsible for climate change has reached the same level of scientific credibility as one of the greatest scientific discoveries of our time, the discovery of the Higgs boson subatomic particle (a basic building block of the universe) in 2012.

What does that mean?

According to this article, it simply means we shouldn't be arguing about "whether global warming" any more, as the scientific team has made the case it doesn't make statistical sense to argue:

They said confidence that human activities were raising the heat at the Earth's surface had reached a "five-sigma" level, a statistical gauge meaning there is only a one-in-a-million chance that the signal would appear if there was no warming.

What sort of evidence did the scientists use?

Satellite data. The researchers said that the evidence for global warming reached the five sigma (σ) level in two out of three data sets in 2005, and in 2016 in a third set.

Interestingly, the third data set points towards different conclusions, according to one of the articles.

Professor John Christy, of the University of Alabama in Huntsville which runs the third set of data, said there were still many gaps in understanding climate change. His data show a slower pace of warming than the other two sets.

“You may see a certain fingerprint that indicates human influence, but that the actual intensity of the influence is minor (as our satellite data indicate),” he said.

However, in that same article:

Benjamin Santer, the study’s lead author, said he hoped the findings would win over sceptics and spur action: “The narrative out there that scientists don’t know the cause of climate change is wrong,” he said. “We do.”

What does the study actually say?

The intro to the study puts it in historical context.

Climate science celebrates three 40th anniversaries in 2019: the release of the Charney report, the publication of a key paper on anthropogenic signal detection, and the start of satellite temperature measurements. This confluence of scientific understanding and data led to the identification of human fingerprints in atmospheric temperature.

It's written in surprisingly accessible science-speak. Here's one scientific definition which might be handy if you're a bit rusty on the layers of Earth's atmosphere, like I am:

The troposphere is the lowest layer of Earth's atmosphere and site of all weather on Earth. The troposphere is bonded on the top by a layer of air called the tropopause, which separates the troposphere from the stratosphere, and on bottom by the surface of the Earth.

Armed with a renewed sense of troposphere, I confidently attacked the conclusions of the study:

Because of this confluence in scientific understanding, we can now answer the following question: when did a human-caused tropospheric warming signal first emerge from the background noise of natural climate variability? We addressed this question by applying a fingerprint method related to Hasselmann's approach (see Supplementary Information 1). An anthropogenic fingerprint of tropospheric warming is identifiable with high statistical confidenc in all currently available satellite datasets (Fig.1). In two out of three datasets, fingerprint detection at a 5σ threshold - the gold standard for discoveries in particle physics - occurs no later than 2005, only 27 years after the 1979 start of the satellite measurements. Humanity cannot afford to ignore such clear signals. [emphasis mine]

References

https://www.nature.com/articles/s41558-019-0424-x
https://www.straitstimes.com/world/evidence-for-man-made-global-warming-hits-gold-standard-scientists
https://eandt.theiet.org/content/articles/2019/02/anthropogenic-climate-change-evidence-reaches-gold-standard/
https://www.news18.com/news/world/evidence-for-man-made-global-warming-hits-gold-standard-scientists-2048549.html

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