Agricultureʹs influence on climate during the Holocene

This paper summarizes the variations of trace gas behaviour and climate during the Holocene (approximately the last 10,000 years), with reference to the last four ice age cycles. The industrial era, commonly regarded as commencing during the 18th century, is one noted when atmospheric greenhouse gas increases due to burning of fossil fuels and land use changes have been attributed to increases in global average near-surface temperatures, particularly in the latter part of the 20th century. However, analysis by Ruddiman has noted that in the Holocene during the period of civil society, the changes in atmospheric greenhouse gases have been anomalous compared with the geological record of the last 400,000 years. During this period, both carbon dioxide (CO2) and methane (CH4) increased, probably as a result of the introduction of agrarian agriculture and land clearing in Eurasia. These, and other land use changes because of agrarian rural activities, may have caused a subtle forcing of climate, preventing climate cooling which might have been expected because of natural forcing. If future evidence supports the Ruddiman hypothesis, then agricultural and forestry activities during the period of civil society may have been exerting an influence on climate for, at least, the last 8000 years.