Rice, Cattle, and Corn: Agriculture, Climate, and the Interglacial. Dan Britt University of Central Florida

Transcription

1 Rice, Cattle, and Corn: Agriculture, Climate, and the Interglacial Dan Britt University of Central Florida

2 What is Normal?

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4 Eccentricity Precession Tilt

5 Our peak solar input was about 8,000 years ago. Solar input is dropping, but the ice is not advancing. What is going on? The other part of the equation are greenhouse gases.

6 Our peak solar input was about 8,000 years ago. Solar input is dropping, but the ice is not advancing. What is going on? The other part of the equation are greenhouse gases.

7 The Greenhouse Effect The average surface temp of the Earth is about 15 C. But the back radiation to space averages - 16 C. This difference of 31 C is the greenhouse effect.

8 What are Greenhouse Gasses? The Greenhouse Effect Any gas molecule with two atoms of different elements. Water vapor (H 2 O) 1-3% Carbon dioxide (CO 2 ) 0.04% Methane (CH 4 ) %

9 Muir Glacier 1941 The Carbon Balance Muir Glacier 2004

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13 Muir Glacier 1941 Muir Glacier 2004

14 Ice Core Layering 19 cm This shows 11 annual layers Summer layers are lighter, winter darker Note the bubbles..

15 These bubbles trap the current atmosphere 36Cl from 50s & 60s nuclear testing in US glacier ice

16 What do the bubbles tell us? CO2 and CH4 march in lock step with ice volume. During glacial max atmospheric CO2 dropped to <200 ppm (it is now ~390) That removes about 180 billion tons of carbon from the atmosphere.

17 The greenhouse gas content of the atmosphere started moving off the historical trend about 8,000 years ago. About when our ancestors invented agriculture and started clearing forests.

18 Why is there agriculture? You read antro texts and you wonder why anyone would stop being a hunter/gather? Evidence of agriculture Rye ~10,000 BC Barley ~9500 BC Planned cultivation ~9,000 BC Wheat and Rice ~8,000 BC Sowing and harvesting ~ 7000 BC Maize ~ 3000 BC

19 Terracing dates back about 5,000 years.the only limiting factor is a source of water

20 And early agriculture was like this. How did ancient peoples prepare fields for planting? Fire. Widespread decrease in elm pollen across Europe after 8000 BC What was happening was deforestation on a massive scale as agriculture spread. Caesar's descriptions of France and England Note that Doomsday Book (1086) had 85% of the arable land in England in crops or pasture

21 Our ancestors invented rice cultivation and domesticated livestock. That was at the same time as methane moved off its historical trend.

22 Why does Rice cultivation increase methane?

23 Rice cultivation started out in swampy terrain, but once you ran out of swamps.

24 Why are there Glaciers?

25 Terracing dates back about 5,000 years.the only limiting factor is a source of water

26 Domestication of animals Dogs ~ 15,000 BC Sheep ~ BC Goat ~ BC Pig ~ 9000 BC Cow ~ 8000 BC Horse ~ 4000 BC

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28 What if something happens to population? Around 1500 the population of the whole Earth was about 500 million What would happen if we removed 1/5 of the world s population? Large areas of forest would grow back, taking CO2 out of the atmosphere Irrigated terraced fields would fall into disuse reducing the methane input After about 100 years the full effect would be felt.

29 In 1491 the population of our hemisphere was probably around million By 1600 it had collapsed to around 5 million Population of central Mexico was around million before Cortes, it dropped to ~1 million by 1600 (Spain had 10 million people in 1492) It was not until the 20 th century that the population of Mexico recovered.

30 What caused the population collapse? Europeans & Asians had long been living with domesticated livestock. Livestock is not just a food source, we share diseases through mutation.. Avian flu becomes human influenza Bovine rinderpest becomes measles Horsepox becomes smallpox Pigs transmit anthrax, brucellosis, leptospirosis, trichinosis, flu, and tuberculosis Europe and Africa were full of diseases that could thrive in American climates, but just had not been transported there Malaria Yellow Fever

31 The Little Ice Age A cold period beginning about 1600 and lasting until about 1900

32 Events during the Little Ice Age The first Thames frost fair was in 1607; the last in The Great Frost of , the worst recorded in England. Solid ice was reported extending for miles off the coasts of the southern North Sea Curling became a popular sport in Scotland. Grape cultivation disappeared from England. Grain cultivation failed in Iceland

33 The Black Death The French Revolution The Industrial Revolution

34 Our peak solar input was about 8,000 years ago. Human activity, through agriculture, has been prolonging the interglacial But, by 1800 we had reached the limits of what we could do with agriculture. And solar input was still dropping.

35 To raise the CO2 level from 260 to 280 ppm took about 80 gigatons of carbon That s about 12% of the whole vegetation biomass! Which is about right considering the impact of agriculture. To do any more we needed to tap a new reservoir..

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