The Civilization Record
Climate and Atmosphere
As humanity grew it changed not only the land surface and the energy system, but also the composition of the atmosphere.
For tens of thousands of years the amount of carbon dioxide and methane in the atmosphere varied within narrow bands inside natural cycles. With the start of farming, the human effect on the atmosphere began to become visible; in the industrial age, fossil-fuel use took that effect to a completely different scale.
Coal, oil and natural gas moved carbon that had accumulated underground over millions of years into the atmosphere in a short time. The transformation of forests and other ecosystems added to this. CO₂ and CH₄ concentrations rose; the global average temperature rose relative to the pre-industrial period.
Today tens of billions of tonnes of new CO₂ are added to the atmosphere each year, and the amount accumulated since the industrial age reaches trillions of tonnes. So the atmosphere records not just the visible mark of civilisation on the planet but its mark accumulated at a global scale.
Worth knowing
Atmospheric CO₂ is higher than at any point in the last 3 million years (the Pliocene).
The current rate of CO₂ rise is about a hundred times the fastest known natural increase.
Ruddiman's early-anthropogenic hypothesis: early farming (forest clearing, rice paddies) may already have nudged CO₂ and CH₄ up in the mid-Holocene, contested.
Total annual greenhouse-gas emissions are around 53 Gt CO₂-equivalent (GWP-100).