Nature reports:

How early in Earth’s history would scientists have been able to detect human-caused climate change if they’d had the proper technology? That’s the subject of a thought experiment published by researchers today in Proceedings of the National Academy of Sciences.

he answer: “As early as 1885,” says study co-author Benjamin Santer, an independent climate scientist based in Los Angeles, California. That’s when researchers could have “confidently disentangled” a human-caused signal of climate change from natural variations, or noise, in the data, he says.

Scientists Eunice Newton Foote and John Tyndall first discovered the heat-absorbing effects of carbon dioxide in experiments they ran independently in the 1850s. But it wasn’t until more than a century later that the scientific community agreed it was clear that rising emissions of CO₂ and other gases were causing Earth to warm.

Santer and his colleagues, however, now say that unmistakable signs of human-caused, or anthropogenic, climate change would already have been around before the end of the nineteenth century — a time when atmospheric CO₂ concentrations were starting to rise because of the Industrial Revolution in Europe, but were still much lower than today. And such signs would have been detectable, if modern technology were available then. [Continue reading…]