There is now evidence that ancient farming practices led to a rise in the atmospheric emission of the heat-trapping gases, a rise that has continued since, unlike the trend at any other time in Earth's geologic history. But, without this human influence, by the start of the Industrial Revolution, the planet would have likely been headed for another ice age.
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 team from the University of Wisconsin, Madison studied the findings based on a sophisticated climate model that compared our current geologic time period, called the Holocene, to a similar period 800,000 years ago.
It shows the earlier period, called MIS19, was already 2.3 degrees Fahrenheit (1.3 degree C) cooler globally than the corresponding time in the Holocene, around the year 1850. This effect would have been more noticeable in the Arctic, where the model shows temperatures were 9-to-11 degrees Fahrenheit colder.