Stephen Vavrus of the University of Wisconsin recently said that “had it not been for early agriculture, (the) Earth’s climate would be significantly cooler today”. Farming from over a millennia ago, such as planting wheat, raising livestock and creating rice paddies, led to a rise in emissions that fundamentally altered the earth’s climate.
These findings are based on sophisticated climate models that compared the current geologic time period, the Holocene, to MIS19, a similar period around 800,000 years ago. It showed that MIS19 was around 1.3 degrees Celsius colder globally than the equivalent point in the Holocene, around 1850. The effect would have been more pronounced in the Arctic, around 5.5 °C cooler. Climate reconstructions show the geological periods starting with similar carbon dioxide (CO2) and methane (CH4) concentrations, with the MIS19 showing a steady drop whilst the Holocene showed a rise in levels around 5,000 years ago, hitting a peak in 1850; researchers stopped the model at the start of the Industrial Revolution due to the sudden increase in emissions.
These observations are placed within the larger natural phenomenon of the Milankovitch cycle where periodic changes in the shape of the Earth’s orbit affect its climate, leading to glacial and interglacial periods. Interglacial periods usually start with higher levels of CO2 and CH4 that gradually drop leading to cooler conditions. But William Ruddiman found this processed reversed around 7,000 years ago, during research into trapped gas in Antarctic ice. Ruddiman commented, “the only explanation I could come up with is early agriculture”. Climate systems have been matched with geological evidence to show that without this increase in emissions the Holocene would by now likely have followed MIS19 and other interglacial periods into another glacial period. The reality is a fundamental alteration to our global climate that leaves us in uncharted territory.
Applicants for Earth Sciences can discover more about the climate models used in this research and try to suggest other natural occurrences that may have contributed to the observed increase in greenhouse emissions.