1. The Anthropogenic Greenhouse Era Began Thousands of Years Ago by William F. Ruddiman
Faisal Abd Razak
ESS 433

2. Hypothesis
Anthropocene actually began thousands of years ago as a result of the discovery of agriculture and subsequent technological innovations in the practice of farming

3. Arguments Cyclic variations in greenhouse gases
Explanations on natural forcing for mid – to late- Holocene can be rejected based on paleoclimatic evidence
Historical evidence point out to viable explanations tied to anthropogenic changes.

4. Early Anthropogenic Greenhouse Emission
Cyclic Variations in CO2 and CH4 driven by Earth-orbital changes during the last 350,000 years predict decreases throughout the Holocene
However, the CO2 trend began an anomalous increase 8000 years ago, and the CH4 trend also increases 5000 years ago.

5. Early Anthropogenic Methane Emission
The anomalous late Holocene CH4 increase cannot be explained by natural forcing, when natural processes lost control of methane trends
For hundreds of thousands years, the CH4 in Vostok ice followed the 23,000 years orbital insolation cycle
It is coincides closely with the innovations in agriculture that produce methane in abundance
Measured CH4 increase of 100 ppb can be explained by a simple linear scaling of 1990 population and anthropogenic CH4 emissions to 1750 population levels
But the full 250-ppb anomaly was most likely due to the inefficiency of early rice irrigation, where extensively flooded wetlands harboring numerous weeds

7. Early Anthropogenic CO2 Emission
Much more abundant gas than methane, variations have had a larger climatic impact over all time scales

9. Pre-Industrial Land Clearance
Can explain the Holocene CO2 rise

11. Pre-industrial forest clearance in Eurasia explains he CO2 rise between 8000 yrs BP and 1800 AD
Validated by 3 tests
1. Clearance must begin near 8000 yrs BP (when the CO2 rise began) on a small, yet ‘non-negligible’ scale
2. Clearance must grow large enough by ~2000yrs BP to explain ~80% of the pre-industrial CO2 anomaly
3. the negative CO2 oscillations of 4 to 10ppm after 2000 yrs BP also need an explanation

12. Test 1: Significant land clearance occur near 8000 yrs BP
Agriculture in Europe consisted of slash-and-burn clearance of small patches of forest, planting of crops, and movement from site to site
Alteration becomes far noticeable after the arrival of bronze-age plows near 6000 to 5000 years BP
A pervasive decrease in forest pollen in China by 6000 yrs BP due to increase disturbance of natural vegetation by human

14. Test 2: Extensive deforestation occur by 2000yrs BP
Almost every major food crop grown today was cultivated by 2000 yrs BP
From calculation of many factors, about ~85-95% target validate the hypothesis that humans caused the rise in CO2 after 8000yrs BP
Forest clearance appears to have been by far the major early-anthropogenic source of carbon

16. Test 3: Why did several CO2 minima interrupt the rise after 2000 yrs BP
Local and regional epidemics, pandemics
The deaths of tens of millions of people because of plague would slow the long term rate rise of carbon emission
Caused the abandoned of farms and rural villages, where extracted carbon from the atmosphere
Black Death ( AD) correlates to CO2 anomaly of -5 to – 10 ppm in the ice core records

18. Effect of Early Anthropogenic Greenhouse Gasses on Climate
Large areas of high terrain would be at glaciated threshold today due to the absence of the industrial-era warming
Altitude of the glaciation limit during the Little Ice Age would have been lower about ~2 degrees C cooler
Significant part of Northeast Canada should have been glaciated in last millennial
Ice sheet should have begun to grow in the last yrs based on the numerical model

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