Human influence on climate detectable in the late 19th century

Area of Science:

• Climate Science
• Atmospheric Physics
• Paleoclimatology

Background:

• The heat-trapping properties of carbon dioxide (CO2) were known in the 19th century.
• Fossil fuel combustion has significantly increased atmospheric CO2 levels.
• Previous research has not explored the historical detectability of climate change with modern tools.

Purpose of the Study:

• To determine when human-caused climate change could have been detected in the 19th century.
• To apply modern climate models and observational network assumptions to historical data.
• To assess the earliest possible detection of anthropogenic climate signals.

Main Methods:

• Utilized state-of-the-art climate models in a thought experiment.
• Assumed accurate atmospheric temperature measurements were available from 1860.
• Applied a standard "fingerprint" method to identify climate change signals.

Main Results:

• A distinct cooling trend in the mid- to upper stratosphere was identifiable by approximately 1885.
• This stratospheric cooling is primarily driven by anthropogenic CO2 increases.
• Detection remained feasible even with Northern Hemisphere mid-latitude data only, by 1894.

Conclusions:

• Human-caused climate change, specifically stratospheric cooling, was detectable with high confidence by the late 19th century.
• The stratosphere offers favorable signal-to-noise characteristics for early climate change detection.
• Evidence suggests a discernible human influence on atmospheric temperature has existed for over 130 years.