'Ancient farmers spared us from glaciers but profoundly changed Earth's climate'
Millennia ago, ancient farmers cleared land to plant wheat and maize, potatoes and squash. They flooded fields to grow rice. They began to raise livestock. And unknowingly, they may have been fundamentally altering the climate of Earth.
A study published in the journal Scientific Reports provides new evidence that ancient farming practices led to a rise in the atmospheric emission of the heat-trapping gases carbon dioxide and methane -- a rise that has continued since, unlike the trend at any other time in Earth's geologic history.
It also shows that without this human influence, by the start of the Industrial Revolution, the planet would have likely been headed for another ice age.
"Had it not been for early agriculture, Earth's climate would be significantly cooler today," says lead author, Stephen Vavrus, a senior scientist in the University of Wisconsin-Madison Center for Climatic Research in the Nelson Institute for Environmental Studies. "The ancient roots of farming produced enough carbon dioxide and methane to influence the environment."
The findings are based on a sophisticated climate model that compared our current geologic time period, called the Holocene, to a similar period 800,000 years ago. They show the earlier period, called MIS19, was already 2.3 degrees Fahrenheit (1.3 C) cooler globally than the equivalent time in the Holocene, around the year 1850. This effect would have been more pronounced in the Arctic, where the model shows temperatures were 9-to-11 degrees Fahrenheit colder.
Using climate reconstructions based on ice core data, the model also showed that while MIS19 and the Holocene began with similar carbon dioxide and methane concentrations, MIS19 saw an overall steady drop in both greenhouse gases while the Holocene reversed direction 5,000 years ago, hitting peak concentrations of both gases by 1850. The researchers deliberately cut the model off at the start of the Industrial Revolution, when sources of greenhouse gas emissions became much more numerous.