You and I, we know climate change is definitely real. But physicists have a gold standard for the burden of proof known as five sigma. A new analysis shows that even the most conservative climate data have passed this point.
Scientists released the analysis of satellite temperature data in Nature Climate Change to mark 40 years of observations. Until satellites came about in the 1970s, scientists had to rely on weather balloons that provided sparse, imperfect data on what was going on in the atmosphere. The satellites were transformative, allowing scientists to improve models, validate past theories about climate change, and generally showing that human ingenuity is astounding. We can measure temperature from space!
To commemorate this achievement, the new study looked at three major satellite temperature datasets which were created using slightly different methods. They then used an analysis to tease out the signal of global warming from the noise of background variability, and charted its significance. For two of the datasets, they found the global warming signal emerged at the five sigma level in just 27 years. But by 40 years, even the most conservative dataset kept at the University of Alabama, Huntsville cleared the five sigma threshold. What that means in everyday language is that there’s a roughly 1-in-3.5 million chance that the warming we’ve seen is due to random chance.
“Five sigma is a big deal for physicists,” Ben Santer, the lead author of the study and climate scientist at Lawrence Livermore National Laboratory, told Earther. “It is the gold standard for discovery in physics. When the announcement was made for Higgs boson, that was the big deal and the detection of particle was at a sigma threshold. Crossing a five sigma ain’t no minor warming.”
At first blush, this may be a milestone only the geeks will celebrate, but it’s bigger than that. The University of Alabama, Huntsville dataset has been a favorite of climate deniers because it shows less warming and a bigger slowdown in warming around the late 1990s and early 2000s. Ted Cruz has cited it multiple times. Denier blogs love it, despite the data being revised to reflect more warming (if you want to get in the weeds on why, read Carbon Brief).
Of course these satellite datasets are only measuring one aspect of global warming, 30,000 feet above where humans live. Down here on the surface of the planet, the impacts of climate change have become increasingly clear because the warming has been more extreme.
Gavin Schmidt, the director the NASA Goddard Institute for Space Studies, shared an analysis with Earther of NASA’s surface temperature data using a smoothed 10-year average to further cut down on the noise. Statistically significant warming emerged around 1980 and passed the five sigma threshold for the 10-year period around 2012.
The new paper puts a nail in the coffin of the tired satellite data argument. Which isn’t to say jabronis like Cruz will stop using it, but now it’s clear to the five sigma value just how bad faith the talking point is.
This article has been updated to include discussion of an analysis provided to Earther by Gavin Schmidt.