Old cultivating practices may have prompted an ascent in the outflow of heat-retaining gasses like carbon dioxide and methane -- a pattern that has proceeded since a recent study has found.
Without this human impact, by the beginning of the Industrial Revolution, the planet would have likely seen another ice age, researchers said.
Millenia back, old ranchers cleared land to plant wheat and maize and potatoes. They overflowed fields to plant rice and started to raise animals. Accidentally, they may have been modifying the climate of the Earth.
"Had it not been for early agriculture, Earth's climate would be significantly cooler today," said Stephen Vavrus, a senior scientist at the University of Wisconsin-Madison in the US.
"The ancient roots of farming produced enough carbon dioxide and methane to influence the environment," said Vavrus, lead author of the study which was published in the journal Scientific Report
The discoveries are based on a climate model that looked at our current geologic era, called the Holocene, to a comparable period 800,000 years ago.
It showed that the period, called MIS19, was at that point 1.3 degree Celsius cooler globally than the Holocene, around the year 1850.
This impact would have been more articulated in the Arctic.
Using climate reconstructions based on ice center data, the model additionally demonstrated that while MIS19 and the Holocene started with comparable carbon dioxide and methane concentrations, MIS19 saw a general drop in both greenhouse gases while the Holocene started seeing the change 5,000 years prior, hitting the top concentrations of the two gases by 1850, and is clearly much more now.
The model was cut-off off towards the beginning of the Industrial Revolution when the types of greenhouse gases started increasing due to numerous human activities.
For the majority of Earth's 4.5-billion-year history, its climate has generally been controlled by a characteristic phenomenon known as Milankovitch cycles, occasional changes in the state of Earth's orbit around the Sun - which varies from more round to more curved - and the manner in which Earth tilts on its axis.
The cycles impact where daylight is distributed on the planet, prompting cold periods or ice ages and also warmer interglacial periods.
The last ice age ended about 12,000 years back and Earth has since been in the Holocene, an interglacial period. The Holocene and MIS19 share comparative Milankovitch cycle attributes.
All other interglacial periods researchers have examined, including MIS19, start with larger amounts of carbon dioxide and methane, which gradually decrease after more than thousands of years, prompting cooler conditions on Earth.
At last, conditions cool to a point where glaciation starts and the cycle goes on.