Clear Signs of Global Warming Date to 1885

Clear signs that humans were affecting Earth’s climate could have been detected as early as 1885 if late-19th-century scientists had possessed the monitoring satellites and computer models that exist today.

That’s the startling conclusion of a study by climate scientists from several leading U.S. climate research centers.

A scientist with Livermore roots, Benjamin Santer, led the study, published this week in the Proceedings of the National Academies of Sciences.

The finding that human effects on climate could have been observed as early as 1885 came as a surprise, Santer told The Independent. Carbon dioxide generated by human activities is the biggest driver of climate change, but much less greenhouse gas was generated in the second half of the 19th century than would be true 100 years later.

Nevertheless, using historical carbon dioxide data from those decades and applying sophisticated computer models, temperature change in the upper atmosphere clearly registered the “fingerprint” of human activity, Santer said.

Santer, who now lives in Oregon, led the study while working at both the Woods Hole Oceanographic Institution in Massachusetts and UCLA. Colleagues were Susan Solomon and Yaowei Li of the Massachusetts Institute of Technology, David Thompson of Colorado State University and the University of East Anglia in the United Kingdom, and Quiang Fu of the University of Washington.

The study grew out of the interest that Santer and others have had in determining how long ago scientists might have detected a human impact on climate if they had known to look for it and had the tools to do so.

It was made easier by the realization that clues to the past are easier to see in the upper atmosphere — the stratosphere — than in the much more turbulent troposphere where we live.

Known for ‘fingerprinting’

As a climate scientist at Lawrence Livermore National Laboratory (LLNL) from 1992 to 2021, Santer was known for establishing the power of climate “fingerprinting” – finding patterns in climate dynamics that were generated by human activities, not by natural fluctuations in daily weather or by long-term cycles, such as El Niño.

In 2023, he and two colleagues from LLNL used fingerprinting to confirm an effect that had been predicted more than half a century earlier — that accumulating greenhouse gases would trap heat in the lower atmosphere and thereby cool the upper atmosphere.

Since 1986, they found, the upper atmosphere had cooled by about 2 degrees Celsius, or 3.6 degrees Fahrenheit, a dramatic 13 times more cooling than could have been produced by natural fluctuations in the same period.

That confirmation was “the clearest evidence I’ve seen in my 30-plus years … of a human fingerprint on climate,” Santer said at the time.

A key factor in that study’s success was the temperature stability of the stratosphere. The lower atmosphere, where we live, experiences temperature fluctuations of tens of degrees in a day, so it’s difficult to attribute small temperature fluctuations with confidence.

In the stratosphere, by contrast, 2 degrees of cooling stood out clearly, leading Santer and other scientists to wonder how early in human history a similar cooling pattern might signal human fingerprints on the climate.

Looking in the 1800s

Could such a signal be seen as early in the late 1800s, long before cars and jet planes? Since carbon emissions are the main culprit in climate change, and humans generated far less carbon dioxide in the 1800s than they do in modern times, it seemed likely that any signal indicating human-caused warming would be small.

Using historical records of atmospheric carbon dioxide, well established in ice core studies, the scientists ran model calculations starting with 1860. Over the next 40 years, to the end of the century, carbon dioxide levels rose only slightly, from 285 to 295 parts per million.

Despite that small rise, the effect on the stratosphere was clearly detectable.

The stratosphere’s temperature is naturally stable and, at most, should have dropped 0.15 degrees C over the four decades from 1860 to 1900, Santer said.

But under the influence of slowly rising carbon dioxide levels from 19th century fires and factories, the models showed the stratosphere’s temperature declining more than three times faster than was natural — 0.5 degrees C, or 0.9 degrees F.

Santer said he was “surprised” to find signs of human-caused climate change so soon after 1860, the starting year of the study. By today’s standards, people were generating “modest amounts” of carbon dioxide, and yet by 1885 the stratosphere already showed early signs of climate change.

‘Bittersweet’

Asked how he felt about the outcome of the study, Santer replied, “Bittersweet.”

On the one hand, he said, the study points clearly to a human influence on the climate, confirming findings that he has been reporting since his early days at LLNL.

On the other hand, we “could have known 130 years ago, before the advent of gasoline- powered cars, that humans were affecting the global climate.”

But instead of acknowledging the reality of the problem, he said, the Trump Administration is treating climate change dismissively and claiming that “climate scientists are alarmists who are frightening the kids.

“That’s concerning to me as a scientist, as a citizen of the United States and as a citizen of this planet,” he said. “Ultimately, you have to address reality. You can’t ignore it.”