7. Changes in the carbon cycle

How is natural climate change a physical explanation for changes in the carbon cycle?

• The quaternary geological period from 2.6million years ago to now shows fluctuations between glacial and interglacial periods

• Carbon and temperatures often rise and fall in line with each other so it’s difficult to decide whether higher temperatures cause more carbon or the other way around

What happened between the 1600’s and 1800’s and what do scientists believe about it?

• A little ice age where the Thames would freeze up for up to 2 months per year

• Scientists believe this was a volcanic eruption where ash and sulphur blocked out the sun causing a cooling effect

• This reflects solar radiation back into space allowing ice sheets to grow due to the high albedo

• However, scientists disagree on when the eruptions were and some scientists just argue there was decreased radiation from the sun

How can cold conditions impact carbon stores?

• Chemical weathering processes may be more active because cold water holds more CO2

• Forest coverage may be less as soil is frozen and water is locked up as snow and ice affecting photosynthesis

• Less carbon would be in the soil store as decomposers would be less effective

How can warm conditions impact carbon stores?

• Melting permafrost increasing the greenhouse effect as methane is released

• Ocean warming can decrease the solubility of CO2 in water releasing it into the atmosphere

Explain how the Earth’s eccentricity (1st Milankovitch cycle) can change the carbon cycles?

• This is the shape of the Earth’s orbit around the sun

• Usually the orbit is circular however sometimes it is more elliptical which may mean cooler conditions in the Northern Hemisphere

• Glaciers may form which will help to store carbon in the glaciers and oceans

Explain how the Earth’s axial tilt (2st Milankovitch cycle) can change the carbon cycles?

• Smaller axial tilt may promote the growth of ice sheets as the Earth is tilting further away from the sun

Explain how the Earth’s precession (3rd Milankovitch cycle) can change the carbon cycles?

• This is the Earth’s wobble as it spins on the axis

How are wildfires a physical contributor to changes in carbon cycle?

• Transfer carbon from biosphere to atmosphere. They can encourage the growth of plants long term.

• 2013 Indonesian fire saw combustion turning the forests from a carbon sink into source

• Wildfires may be started on purpose and may cause destruction of homes or health conditions

How volcanic activity is a physical contributor to changes in carbon cycle?

• Ash and sulphur dioxide have a cooling effect reflecting sunlight away from the Earth eg: Pinatubo 1991 which caused a dip in global temperatures for 2-3yrs

• 100-300million tonnes of carbon is released from volcanos per year

• Short term cooling, long term warming

How is hydrocarbon extraction and use by humans changing the carbon cycle?

• It is the extraction and burning of fossil fuels (eg: crude oil) which releases CO2 into the atmosphere. Without human intervention the carbon would stay sequestered for millions of years

• Cement manufacture (made when calcium carbonate is heated) produced 5% of anthropogenic CO2 emission. However, these emissions are dominated by China and USA.

• Links to fast fashion and industry and our carbon footprint

How does deforestation impact the carbon cycle?

• Often trees are cleared to make way for urban development or agricultural land → roads to access remote areas

• The equivalent to the size of Greece in trees is cut down each year and converted into other land use

• Accelerates rate of decay and impacts water cycle not allowing evapotranspiration. Also, soils become dry unprotected by shade.

• Slash and burn techniques where farmers cut down and burn trees creating fertile ash for soil

• Carbon from biosphere → atmosphere. Especially old trees which stored lots of carbon

Explain farming practices as a human way of changing the carbon cycle?

• Ploughing allows air into the soil which increases microbial activities like decomposition releasing CO2. Also, CO2 from tractors

• Animals release methane when they respire and digest food, specifically cows. This is the largest source of carbon in agriculture.

• Rice paddies generate 10% agricultural emissions from methane from the bacteria in the waterlogged soil

• Most agriculture related CO2 emissions come from Asia according to UN - 50% of world population relies on rice

How do land use changes impact carbon cycle?

• Changes to urban land uses account for 30% of anthropogenic CO2 emissions

• Emissions originate from transport, industry, and land development - cement industry

• Concrete production releases a lot of CO2, low albedo, impermeable so less infiltration

• Vegetation removed, less infiltration

Describe carbon sequestration as changing levels in the carbon stores?

• Involves capturing CO2 from the atmosphere and putting it into long term storage - very expensive

• Geological sequestration - CO2 is captured at its source eg: power plants and then injected as a liquid into stores underground eg: ocean however, this is still in the experimental stage

• Terrestrial sequestration - using plants to capture CO2 which may benefit wildlife. However, sequestration plantations often require monitoring for decades and the carbon is never fully removed/can be released in a wildfire

Describe the enhanced greenhouse effect as changing carbon stores impact on the atmosphere?

• Process which is causing global warming due to anthropogenic production of CO2. These gases trap radiation from the sun.

• Short wave more penetrative radiation from the sun comes to the Earth.

• Some of the radiation is absorbed into the Earth’s surface

• Long wave infrared radiation is often re emitted by greenhouse gas molecules either back to the Earth or up into the atmosphere.

Describe radiative forcing?

• Where extra CO2 and greenhouse gases cause radiation to be reflected into the Earth and atmosphere causing a net gain/loss of radiation

• Means the Earth’s energy budget is out of balance.

What are the causes of the enhanced greenhouse effect?

1. Land use change - Cattle ranching produces large amounts of methane eg: in the Amazon 70% of the land is used for cattle ranching.

2. Fertilisers - these and rice padi fields produce lots of greenhouse gases. However, more sustainable substitutes like quinoa are being used which require less water

3. Deforestation - reduces carbon sequestration and trees become carbon source

4. Urbanisation - concrete has low albedo, cement releases CO2 during production. Increasing CO2 emissions for transport, energy consumption etc uses fossil fuels by combustion releasing CO2 eg: NA releases 15.6tonnes of CO2 per capita