Climate Change and Agriculture

• Effects of agriculture on climate change

• Effects of climate change on agriculture

• Most of the effects of agriculture on climate change revolve around greenhouse gases.

- CO2

- CH4

- N2O

• There are also albedo effects.

Climate Change and Agriculture

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• Land clearing is the leading source of agricultural CO2.

Agriculture and CO2

• Forests are much more efficient carbon sinks than farmland.

• Farms waste “carbon space” vertically and horizontally.

Agriculture and CO2

• Agriculture also creates soil disturbance and increased rates of organic decomposition – both result in CO2 release.

Agriculture and CO2

• Soil erosion resulting from agriculture further reduces the land’s ability to uptake carbon.

Agriculture and CO2

Agriculture and CO2

• Forest area in the United States between 1620 and 1920 AD.

Agriculture and CO2

Agriculture and CO2

• Brazil contains 30% of the world’s rainforest.

• That is almost 13 Long Islands a year!

Agriculture and CO2

• Borneo losing 5000 square miles a year (3.6 Long Islands).

• Why? …

Agriculture and CO2

• China - high demand for wood (housing, flooring, furniture).

• Forest is replaced with Palm plantations (palm oil a key ingredient in detergent, soaps, cosmetics, foods, etc.).

Agriculture and CO2

• “Slash and burn” agriculture creates CO2 as part of the deforestation process.

Agriculture and CO2

• Methane is a byproduct of many agricultural activities.

• Current concentration in the atmosphere is 1700 parts per billion – preindustrial concentration was less than half of that (700 ppb).

• 21 times more effective greenhouse gas than CO2.

Agriculture and CH4

Agriculture and CH4

• Main agricultural sources are rice paddies, livestock, and termite mounds.

• Landfills, swamps, biomass burning also significant sources.

• Bacteria need oxygen just like we do. In environments where O2 is not available, bacterial will use CO2 as an oxygen source (CO2 in, CH4 out) - anaerobic respiration.

• Standing water with lots of organic matter will quickly turn anaerobic.

Agriculture and CH4

• Typical rice paddy is submerged at least 4 months a year.

Agriculture and CH4

• Rice agriculture contributes 50-100 million tons of CH4 per year to the atmosphere – this is the largest anthropogenic source.

• What to do about it?

• Experimenting with varieties that don’t require as much water, and denser-growing varieties (more rice per paddy).

• Using specific fertilizers can also make a difference.

Agriculture and CH4

Agriculture and CH4

• Livestock (cows in particular) are the next major agricultural source of methane.

• 100 million tons per year.

• Comes from bacteria living in the animals’ stomachs and intestines.

Agriculture and CH4

Agriculture and CH4

• Decomposition of cow and chicken manure accounts for another 25 million tons of methane.

• Some of this gets collected in slurry tanks (“biogas”) and is used as fuel.

Agriculture and CH4

• Deforestation in the tropics leaves a lot of dead wood that is quickly colonized by termites.

Agriculture and CH4

• Natural methane sources:

Agriculture and CH4

• Anthropogenic methane sources:

• Energy- and ruminant-related methane dominate.

Agriculture and N2O

• Nitrous oxide – “laughing gas.”

• Relatively low concentrations (300 ppb now, 275 ppb pre-industrial).

• 310 times more effective greenhouse has than CO2.

• Similar to anaerobic methane production, bacteria in low/zero-oxygen environments convert nitrite (NO3) to nitrogen gas (N2) and nitrous oxide (N2O).

Agriculture and N2O

• The use of man-made fertilizers rich in nitrogen compounds contributes to N2O production in soils.

• 2-4 million tons of N2O from this source per year.

• Widespread use of animal manure as fertilizer can release substantial amounts.

Agriculture and Climate

• But when did all of this really start?

Agriculture and Climate

• Recently been speculated that humans may have been influencing climate for much longer than previously thought.

Agriculture and Climate

Agriculture and Climate

• When human population decreased, CO2 levels decreased.