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Human-caused stratospheric cooling may have been detectable as early as 1885

A small, multi-institutional team of climate scientists has found evidence that human-caused impacts on the stratosphere began earlier than previously thought. In their study, in the Proceedings of the National Academy of Sciences, the group used observational data, environmental theory and computer modeling to create simulations depicting the state of the stratosphere to a time just after the dawn of the industrial age.

Sometime during the 1850s, scientists discovered that carbon could trap heat—but it took another century for scientists to agree that rising CO₂ in the atmosphere was causing global warming. Such findings came about due to improvements in technology, such as satellites, weather balloons and ground-based monitoring stations around the globe.

The team first posed a simple question: How far back in time could changes to the stratosphere due to human activities be observed if modern tools had been available?

To find out, they embarked on a study of the stratosphere—the part of the atmosphere above the troposphere. As greenhouse gases warm the planet, the stratosphere grows cooler. This cooling is less impacted by changing weather patterns and is thus a more reliable means of detecting changes wrought by human activities.

In modern times, temperatures in the stratosphere can be taken using satellite data. To predict changes in stratospheric temperature before modern tools arrived, the research team used historical data, theory and nine climate models to predict the impact of human-based emissions on temperatures in the stratosphere going back to 1860—the beginning of the industrial age. They found that evidence of changes to the stratosphere due to human activities would have been detectable as far back as 1885.

This was prior to the introduction of automobiles. But humans have been releasing carbon into the atmosphere in other ways for thousands of years through burning coal, wood and other materials, for heating, cooking and manufacturing.