1.12. Changes To The Carbon Cycle

Question 1

Fossil fuel extraction and combustion evidence

Answer 1

• Burning of coal, oil and gas releases 90% of Co2 into the atmosphere
• Annual emissions are 61% higher than 1990 - China (28%), USA (14%) and India (7%)

Question 2

How does fossil fuel extraction and combustion affect the carbon cycle?

Answer 2

The biosphere and hydrosphere are only able to absorb half of this excess, resulting in the atmospheric carbon store swelling by 80ppm since 1960.

Question 3

Cement manufacturing evidence

Answer 3

• Cement production releases 5% of all Co2 emissions into the atmosphere
• For each 1000kg of cement produced, 900kg of Co2 is released into the atmosphere

Question 4

How does cement manufacturing affect the carbon cycle?

Answer 4

Calcium carbonate is heated to separate lime and carbon dioxide -> heat often comes from burning fossil fuels

Question 5

Farming processes evidence

Answer 5

• 44% of agricultural Co2 comes from Asia, 25% from Americas

Question 6

How do farming processes affect the carbon cycle?

Answer 6

• Animals release Co2 and methane when respiring and digesting food
• Ploughing can release Co2 -> microbial activities increase in soil layers inverted by ploughing, resulting in increased respiration
• Growing rice in paddies releases methane
• Increased population increases food production

Question 7

Deforestation evidence

Answer 7

• 13 million hectares of forests cleared for agriculture, logging or way to make developments
• 3% of forests lost between 1990 and 2005 at 200km squared per day

Question 8

How does deforestation affect the carbon cycle?

Answer 8

Clearance reduces the size of the carbon store and if cleared forest is burned, there’s a rapid flow of carbon from biosphere to atmosphere

Question 9

Land use change evidence

Answer 9

• Urban areas grow by 1.3 million people every week -> more than 50% of the population
• 2012: cities responsible for 47% of global carbon emissions

Question 10

How does land use change affect the carbon cycle?

Answer 10

• Come from switch from natural vegetation to urban surfaces
• Increased energy consumption for transport, industry and domestic use
• Cement manufacture for urban dwellings

Question 11

Carbon sequestration evidence

Answer 11

• Power station built in Canada -> burns coal, captures the emissions and powers 100,000 houses in the area

Question 12

How does carbon sequestration affect the carbon cycle?

Answer 12

• Injecting captured Co2 as a liquid deep underground into a variety of stores
• Terrestrial sequestration-> use of plants to capture Co2 from the atmosphere, carbon stored as biomass in stems, roots and nearby soils -> stored carbon can be lost through forest fire -> slow growing and not permanent

Question 13

Natural wildfires evidence

Answer 13

• Negative feedback loop

Question 14

How do natural wildfires affect the carbon cycle?

Answer 14

• Rapidly transfer large quantities of carbon from biomass to atmosphere
• Loss of vegetation decreases photosynthesis so less carbon removed from the atmosphere
• Long term -> fires can encourage growth of new plants, take in carbon from atmosphere for photosynthesis
• Fires can have a neutral effect on amount of atmospheric carbon

Question 15

Volcanic activity evidence

Answer 15

• Recent eruptions have released much less Co2 than human activities (1% of total)

Question 16

How does volcanic activity affect the carbon cycle?

Answer 16

• Releases carbon stored within the earth in magma in the atmosphere
• There is potential for a very large eruption to disrupt the carbon cycle significantly
• Intense Co2 release in the geological past caused enough increase in atmospheric Co2 levels to cause a rise in temperature and possible mass extinctions

Question 17

Natural climate change evidence

Answer 17

• Over the last 2.6 million years, global climates have fluctuated between warm and cold periods
• Milankovitch cycles - every 100,000 years, Earth’s orbit become more elliptical, triggering ice ages

Question 18

How does natural climate change affect the carbon cycle?

Answer 18

During cold periods:
- Carbon stored as biomass would have become incorporated into permafrost = less atmospheric Co2
- Increased chemical weathering (cold water holds more Co2). As a result, more Co2 is transferred from the atmosphere
- Oceans are more saline during cold periods. They take up greater amounts of carbon from the atmosphere via the oceanic pump.