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Climate contrarians predicted the world would cool—it didn’t – Ars Technica


A stylized photograph of the Sun renders it blue.

Modern climate science is old enough for many of its early predictions to be checked against evidence—the overall global warming trend; specific patterns like nighttime warming exceeding daytime warming; or the cooling of the stratosphere. Even with all that new evidence, the estimated amount of warming you get for a given amount of greenhouse gas emissions hasn’t really changed since 1979.

The flip side to this is also true. Those who have opposed climate science’s conclusions—they’re a broad menagerie, including scientists in different fields, politics-obsessed bloggers, and think-tank employees—have also been squawking long enough for predictions to be tested. Despite their alternate-reality insistence that climate science never predicted anything, these contrarians don’t spend much time showing off their own predictions’ track record.

The reason for that is that the track record is very, very bad. Like the cringeworthy poetry you wrote in high school, they probably hope that everyone will just forget about it.

What goes up must come down

Before we turn on the scoreboard, it’s worth reviewing some commonalities of these predictions. Most of them appeal to cycles—particularly solar cycles. This lets them place any alarming upward trend in the comforting blanket of a downward trend that is just around the corner.

The Sun goes through an 11-year cycle of activity, which has been apparent for a very long time from records of sunspots. The length of the cycle is quite consistent, driven by an oscillation of the Sun’s magnetic field. The magnitude of change over each cycle does vary, though, including famous “minimum” periods where sunspots were nearly absent across multiple cycles.

While this cycle does produce a measurable variation in solar radiation, the effect on Earth’s climate is quite small. Scientists who study our atmosphere, weather, and climate know this. Some scientists who study the Sun, however, have managed to escape awareness of this fact and attempted to explain (or predict) every wiggle in Earth’s climate based on the timing of solar cycles.

Beyond the Sun, this mathematical but physics-free approach has led to many confident but false predictions. In any data with variance, one can find signals of cycles of various lengths. Some will be meaningful—like annual cycles in temperature or oscillations of El Niño and La Niña conditions in the Pacific—while others will simply be coincidental.

If you look hard enough, you can find a specific data set and specific time period where a particular cycle length shows up. Make up a good story to go with the curve you fit to that spurious cycle, and you can write a persuasive blog post about what will happen next. Of course, reality doesn’t read your blog and is famously difficult to persuade.

Must replenish my strength with rays of the Sun

For comparison with past predictions, we’ll use NASA’s global surface temperature data set—though any of the major data sets would do. In the reality that is tracked by this data set, each year from 2015 through 2020 turned out to be warmer than any year previous to 2015.

The specific predictions we dug up were made between 2005 and 2013. To be accurate, these predictions would have to account for the long-term warming trend of the preceding decades. But accounting for warming would undermine the whole endeavor of labeling climate change a “hoax,” so none of these predictions did.

NASA’s global surface temperature record through 2020.
Enlarge / NASA’s global surface temperature record through 2020.

2008, Don Easterbrook (source): “global climates can be expected to cool over the next 25-30 years[…] The real danger in spending trillions of dollars trying to reduce atmospheric CO2 is that little will be left to deal with the very real problems engendered by global cooling.

Easterbrook, a retired professor of geology, makes this claim based on the appearance of roughly 30-year fluctuations in a Greenland ice core. Inappropriately extrapolating this local record to the entire globe, he declared that warming between 1977-1998 was entirely due to this unidentified cycle. That would mean 30 years of cooling was next—physics of the greenhouse effect be damned.

He repeated this claim over a number of years, starting in 1998, when he predicted that temperatures would start dropping in the first decade of the 2000s. They did not.

2009, Henrik Svensmark (source): “In fact global warming has stopped and a cooling is beginning[…] Everything indicates that the Sun is going into some kind of hibernation[…]

Svensmark is a Danish physicist who long pushed a hypothesis that climate should fluctuate with solar and orbital cycles because incoming galactic cosmic rays—which are less common when the Sun’s magnetic field deflects more of them—controlled the production of condensation nuclei for clouds.

An experiment at CERN was actually built to test this mechanism, which didn’t pan out. It’s no surprise, then, that the predictions of imminent cooling (including those in his 2007 book titled The Chilling Stars: A New Theory of Climate Change) didn’t pan out, either.

2010, Anastasios Tsonis (source): “We have such a change now [of ocean oscillations] and can therefore expect 20 or 30 years of cooler temperatures[…] Perhaps we will see talk of an ice age again by the early 2030s, just as the [ocean oscillations] shift once more and temperatures begin to rise.

Tsonis—a retired professor of atmospheric science—was a temporary star of the climate contrarian movement for his repeated assurances of a cooling trend. Like Easterbrook, this was based on natural oscillations around 30 years long. Specifically, Tsonis appealed to known ocean oscillations in the Pacific and Atlantic.

This fed off the meme that warming had stopped in 1998—a cherry-picked year that was anomalously warm—and thus the cycle had already turned downward. As late as 2013, Tsonis was on Fox News saying that “I would assume something like another 15 years of leveling off or cooling.” Unlike global temperatures, that prediction isn’t looking so hot.

2011, Nicola Scafetta (source): “The climate will likely stay steady until 2030/2040 and may warm by about 0.3-1.2° C by 2100.

Scafetta—a physicist who loves to publish papers on topics outside of physics—was the king of fitting wiggly cycles to temperature data and then extrapolating into the future. In this instance, Scafetta claimed that a pile of astronomical cycles with varying lengths was controlling Earth’s climate. Running this mathematical model forward predicted about three decades of small ups and downs followed by a much smaller warming trend than what we see in climate models.

Scafetta’s prediction (blue) and observed temperatures (red) as of 2011.
Enlarge / Scafetta’s prediction (blue) and observed temperatures (red) as of 2011.
Nicola Scafetta

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