At the time when the first locomotives crisscrossed Europe and the combustion engine had just been invented, the atmosphere already reacted to human activity. Long before the major conferences on the climate or modern temperature readings, signs of imbalance began to register in the high layers of air. Thanks to the current tools, researchers retraced these weak signals and reveal that the human footprint on the climate could have been detected from the end of the 19th century, long before the subject was imposed in the public debate.
In this study, the researchers imagined a situation where scientists of 1860 would have had access to today's measurement tools, in particular the satellite radiometers capable of capturing temperature variations at different altitudes. Based on the climatic simulations of the CMIP6 program, they identified a clear signal: progressive cooling of the stratosphere, directly linked to greenhouse gas emissions. This phenomenon, although discreet, would have been identified with certainty from the end of the 19th century, at a time when the first internal combustion engines barely appeared.
This discovery suggests that the human imprint on the climate is not only a contemporary reality, but an old process, started from the beginnings of the industrial revolution. At a time when we did not yet know the concept of anthropogenic greenhouse effect, the atmosphere already recorded the signs of an in progress imbalance.
What the stratosphere reveals to the beginnings of warming
Unlike the temperatures noted on the ground, influenced by local factors such as weather or seasons, the stratosphere offers a more stable and more reliable indicator of long -term changes. Located between 10 and 50 kilometers above sea level, this atmospheric layer cools when the carbon dioxide concentration increases. This apparent paradox is actually a very useful marker for detecting human influence on the climate.
As Science Alert explains, greenhouse gases imprison the heat in the low layers of the atmosphere, preventing part of this energy from climbing to the stratosphere. In parallel, the progressive destruction of the ozone layer reduces its ability to absorb solar radiation. These two combined phenomena cause slow, but constant cooling, high altitudes, while the surface of the earth warms up.
This cooling is a clearer signal than warming on the ground, often disturbed by climatic vagaries. According to the researchers, 25 years of reliable stratospheric measurements, from 1860, was sufficient to detect a significant thermal anomaly. Even with data limited to the average latitudes of the northern hemisphere, scientists could have detected a stratospheric cooling caused by human activity in 1894.
The human footprint on the climate was visible, but ignored
In 1856, Eunice Fote already showed that carbon dioxide could trap the heat. A few years later, John Tyndall confirmed these results with more precision. However, it took almost a century for these experimental observations to turn into a global alert. The slowness of this awareness is not explained only by the lack of technology, but also by an ignorance of the complex interactions between the different strata of the atmosphere.
The models used today make it possible to rebuild past the past climatic signals. They show that from the 1860s, greenhouse gas emissions, although inferior to those of today, were already sufficient to modify the overall thermal balance. This historical discrepancy between the cause and awareness illustrates how understanding of the climate is based on an accumulation of data and a precise reading of weak signals.
The question is therefore not to know if man influences the climate, but rather to understand since when this influence is measurable. However, recent simulations show that the human imprint on the climate is much older than what the first GIEC reports suggested. This observation is not simply retrospective. It also shows the relevance of atmospheric indicators in the evaluation of our impact, and the need to act from the first signals.
A new look at a past that we thought was neutral
The modeling exercise proposed in the journal Pnas is not anecdotal. It makes it possible to reconsider an entire period of industrial history that we still believed out of cause. By overlapping carbon dioxide estimates from ice carrots and atmospheric data rebuilt by models, researchers show that the effects of burnt coal in the 19th century are still visible in the sky archives.
This reconstituted climatic past reminds us that a low level of emissions does not mean lack of impact. Between 1860 and 1899, the atmospheric co₂ level already increased by around 2.5 parts per million each decade. If this figure seems modest compared to current increases, it was part of a world that had not yet known anything like this. The planet already reacted, but no one listened.
By giving a voice to these forgotten signals, current research offers a more nuanced reading of climate change. It shows that classic historical landmarks, such as the start of systematic statements in 1958 or the first climate models in the 1970s, are only the emerged part of a much older phenomenon. And what we thought was a recent crisis is actually a long process, of which we have not realized until very late.
With an unwavering passion for local news, Christopher leads our editorial team with integrity and dedication. With over 20 years’ experience, he is the backbone of Wouldsayso, ensuring that we stay true to our mission to inform.
