During the past few decades, human-induced climate change has been a persistent theme in the scientific literature. In more recent times it has been the subject of considerable argument in the public domain. Central to the discussion of human-induced climate change is the role of greenhouse gas emissions during the industrial era.
But in searching for a human signature in the atmosphere we can go much further back in time and follow the lesser-known idea, championed by W.R. Ruddiman, of the role that early farming played in global climate change over the last few thousand years. Ruddiman’s research, while not without its critics, led to the “early anthropogenic hypothesis” – the idea that through land clearing, raising livestock and irrigating rice paddies, early agriculturalists caused a reversal in natural declines of atmospheric carbon dioxide 7000 years ago and methane by about 5000 years ago, thus steering the Earth into a different climate trajectory.
To this early anthropogenic hypothesis can be added the direct effects that human modifications to the land’s surface may have had on the atmosphere. After all, humans have had a major impact on the Earth’s land surface – specifically its vegetation – for thousands of years.
The extent and severity of global land surface changes has been long recognised in the scientific literature. It was...
