An article recently published in Climate of the Past, an interactive open access journal of the European Geosciences Union, looks at temperature changes from human activity during the Roman Empire.
For the study, an international team of scientists used existing studies on land use under the Ancient Romans to estimate the level of air pollution emitted during the Empire. Then, with a global aerosol-enabled climate model, attempted to quantify the effects humans had on the local environment.
The researchers found that while deforestation and various land use changes had a warming effect of 0.15°C, this was (over) compensated by a cooling effect prompted by the dispersal of aerosol emissions from agricultural burning. The result is an overall drop in temperature of 0.17°C, 0.23°C or 0.46°C (dependent on the low, intermediate, or high emission scenario, respectively).
This cooling effect would not have been universal, however. The results from the model suggest areas in Central and Eastern Europe saw the most extreme cooling, whereas parts of North Africa and the Middle East would have instead experienced warming.
While scientists have been studying the effect of the Roman Empire on Europe's climate for the past two decades, this is apparently the first piece of research to consider the counter-effect of aerosol emissions, says Joy Singarayer, from the University of Reading in the UK.
"The novelty here is in their thinking about what the aerosol contribution would be, which seems to be quite considerable," Singarayer told New Scientist.
In contrast to the climate change of today, it is unlikely this cooling would have been significant enough to have had much of an effect on everyday life in Roman Europe. Particularly, given the Roman Warm Period – a span of natural warming – that took place between 250 BCE to 400 CE.
But agricultural burning may have impacted the weather in other ways, Anina Gilgen from the ETH Zurich in Switzerland told New Scientist. For example, increased air pollution in nearby cities, changes in precipitation patterns and, consequently, water availability.
While it can be hard to accurately gauge past weather events ("Our model may overestimate aerosol-effective radiative forcing, however, and our results are very sensitive to the inferred seasonal timing of agricultural burning practices and natural aerosol emissions over land," the study authors write), the article ultimately concludes: "it is likely that human influence on land and the atmosphere affected continental-scale climate during Classical Antiquity."
[H/T: New Scientist]