The Anthropogenic Greenhouse Era Began Thousands of Years Ago By William F. Ruddiman Presented by Susan Wisehart ESS 433 Autumn 2015

Outline Hypothesis Early Anthropogenic (human) Emissions Pre-Industrial Land Clearance Early Greenhouse Gases Effect on Climate

Hypothesis Anthropogenic greenhouse gases first altered atmosphere thousands of years ago as a result of agriculture Based on three arguments: 1.Anomalous trends in greenhouse gases 2.Rejecting natural process explanations 3. Historical evidence

Early Anthropogenic Emissions Orbital monsoon theory Summer insulation -> heat rises -> lower surface pressure -> draw in moist ocean water -> MONSOON-> releases CH 4

Orbital monsoon cycles cannot explain rise in CH 4

Early Anthropogenic Emissions Why? Humans adapted wild rice to cultivation by 7500 yrs BP and begun irrigation by 5000 yrs BP Vostok Ice CH 4 records give ~250 ppb anomaly attributed to humans Most likely due to inefficient rice irrigation – i.e. flooding -> release of CH 4

Early rise in CO 2 as well Early Anthropogenic Emissions

Pre-industrial Land Clearance Natural orbital cycles don’t explain rise in CO 2, so how about humans? ~320 GtC loss of terrestrial C > industrial output – Loss of C must have started earlier than industrial era

Pre-industrial Land Clearance Tortoise vs. Hare

Hypothesis = pre-industrial deforestation

Pre-industrial Land Clearance Agriculture = deforestation = CO 2 increase in atm. Environmental disturbance most noticeable with the invention of the plow ( yrs BP)

Pre-industrial Land Clearance Anomalous CO 2 rise reached 80% max by 2000 yrs BP Did that much deforestation occur by 2000 yrs BP? Paleoenvironmental evidence says yes – Pollen record – Increased sediment accumulation – Developments in agriculture

Pre-industrial Land Clearance (cont.) Did that much deforestation occur by 2000 yrs BP? A bunch of simple math gives necessary C input value (by deforestation) in the 100s – Historical evidence far surpasses this value – Agriculture in heavily populated Eurasia was booming by 2000 yrs BP

Pre-industrial Land Clearance CO 2 minima still occurred after 2000 yrs BP. Why? THE PLAGUE!

Pre-industrial Land Clearance Human death…but reforestation! = decrease in CO 2 to explain minima

Pre-industrial Land Clearance Additionally, Black Death ( AD) correlates to CO 2 anomaly of -5 to – 10 ppm in the ice core records

Early Greenhouse Gases Effect on Climate In the absence of pre-industrial warming: large areas of high terrain would be at glaciated threshold today Little Ice Age glaciation altitude would have been lower (~2 degrees C cooler) => Northeast Canada should have been glaciated in last millennia

Early Greenhouse Gases Effect on Climate Additionally, Numerical models of ice volume predict ice sheets should have begun to grow in last yrs

Summary Most consistent story = carbon sequestration on farms Conclusion: “Plague outbreaks caused major population reductions…and contributed to cooler climates”

Reference Ruddiman, F. William: 2003, ‘The Anthropogenic Greenhouse Era Began Thousands of Years Ago’.