The slow and fast carbon cycles

What is the slow carbon cycle?

The cycle where the earth tries to keep the balance of carbon stable. This occurs over millions of years.

What is the fast carbon cycle?

The ongoing flow of carbon between the land, atmosphere and oceans.

What are four main factors driving change in the magnitude of carbon stores?

Weathering

Carbon sequestration in oceans

Volcanic activity 

Diffusion 

What three types of weathering drive change in carbon stores?

Chemical weathering

Biological weathering

Physical weathering

How does chemical weathering drive change in carbon stores?

Carbonic acid in acidic rain breaks down rock to release carbon

These chemical reactions take several hundred million years to release carbon

How does biological weathering drive change in carbon stores?

Plants’ roots grow into rock

Small animals burrow into rock

How does physical weathering drive change in carbon stores?

Usually, freeze-thaw weathering exposes a larger surface area of the rock to chemical weathering.

What is carbon sequestration?

The process of trapping carbon.

What happens to the carbon dissolved in ocean waters?

• It is taken up by shell-building animals and plankton to use for growth

• When these animals die, they end up on the ocean floor

• These dead organisms go on to form limestone

• In some places, heat or pressure causes the animal remains to form oil, coal or gas

How is carbon released by tectonic movement?

When a tectonic plate breaks down following subduction, carbon is released.

How do volcanic eruptions contribute to the carbon cycle?

They release CO2 into the atmosphere.

How is volcanic activity linked to weathering?

Increase in tectonic/ volcanic activity

Leads to global temperature rise

Leads to increase in acidic rain

What are the two types of carbon diffusion at the ocean’s surface?

Down-welling - where carbon dioxide diffuses into the water

Up-welling - where carbon dioxide diffuses out of the water

Why has the ocean needed to absorb so much extra carbon?

Due to human activity.

What two factors is the rate of diffusion in oceans controlled by?

Wind currents

Temperature

What four main factors drive change in the fast carbon cycle?

Photosynthesis

Respiration

Decomposition

Combustion

Define photosynthesis.

The process by which plants absorb carbon dioxide and water to produce glucose and oxygen.

Define decomposition.

The process by which biological remains are broken down, releasing nutrients and energy.

What is respiration?

A process in cells and tissues of living organisms where energy is used and CO2 is given off.

Define net primary productivity.

The amount of biomass added in a year.

(we use this to measure photosynthesis)

How does global plant carbon consumption change throughout the year?

• August- more consumption in the north

• December- more consumption in the south

• Consumption corresponds to photosynthesis, when growth is heightened

• This is why carbon consumption is higher in each hemisphere’s summer, respectively

What was the main form of combustion pre-industrial revolution?

Wild or man-made fires.

What is the main form of combustion post-industrial revolution?

Burning fossil fuels. 

How is coal formed?

• Many giant plants died in swamps

• The plants were buried under water and dirt over millions of years

• Heat and pressure turned the remains into coal

How are oil and natural gas formed?

• Sea plants and animals died and were buried on the ocean floor

• They were covered by layers of salt and sand

• Over millions of years, the remains were buried deeper and deeper

• Heat and pressure turned them into oil or gas

What is one of the least clean forms of fossil fuels?

Coal.

What is an example of a clean fossil fuel- what does this mean?

Natural gas is one of the cleanest- it is low-carbon.

How has CO2 in the atmosphere changed due to human activity?

The concentration is now higher than it has been for the last 800 000 years.

What percent of emissions from the cement industry are from burning fossil fuels?

40%

What percent of global population is projected to be urban by 2030?

60%

What percent of the earth’s greenhouse effect is caused by CO2?

20%

When did the industrial revolution begin?

1750.

What percent of pre-industrial levels is the current CO2 concentration?

150%

What was the primary outcome of the 2014 COP conference?

The Lima call for climate action, which advanced negotiations for the Paris agreement.

By what percent has CO2 outgassing by the southern ocean been underestimated?

Up to 40%.

How much CO2 is released by burning fossil fuels each year?

21 petagrams.

What happens to CO2 trapped in trees during wildfires?

It is released

Can be drawn in again by regrown vegetation

Incomplete or slow recovery causes permanent transfer 

Around how many tonnes of C02 does a hectare of wildfire produce?

30-70

What percent of fires’ emissions are from wildfires?

12%

How do old trees burn?

Mainly in low-intensity fires

They burn easily because they are dry

However, old forests that have sustained many low-intensity fires can be strengthened

How do young trees burn?

They burn more in high-intensity fires

They are more moist, so aren’t susceptible to low-intensity fire

What do wildfires do to the level of photosynthesis in a forest?

The environment is changed overall

Reduced light due to smoke and ash reduces photosynthesis

Leaves close stomata to avoid toxins, which reduces their ability to take in CO2

Photosynthesis can be temporarily increased for plants on the lower levels when taller trees are burned away

On average, what is the decrease in photosynthesis over the year following a wildfire?

16.5%

What happens to species diversity in a wildfire?

In some cases, the fire can create a ‘mosaic of habitats’ due to the change in conditions, increasing biodiversity

Frequent or intense fires can cause long-term habitat loss

Food webs are impacted

Wildlife is killed directly by the fire

What is the average decrease in biodiversity in the year following a wildfire?

33%

Why are northern hemisphere forests considered to be carbon sinks?

Most of the world’s biomass is in the northern hemisphere

This means forests in the north sequester more CO2 in total

What happens after a forest fire?

The forest burns

Ash is produced

Ash temporarily fertilises the soil

What impact does a forest fire have on an area?

Reduced biodiversity

Reduced photosynthesis

Reduced air quality

Why has the incidence and severity of forest fires increased in recent years?

Climate change

Hot and dry conditions make wood more likely to catch

Increased incidence of forest fires starts a positive feedback loop

What is a fire break?

A barrier created to stop or slow the spread of fire.

Why is fire suppression good?

It saves lives

It detects and extinguishes fires

It prevents damage to homes and businesses

It provides time to evacuate

Why could fire suppression be considered bad?

It can lead to wildfires of increased severity.

What are the four main types of land use change that affect the carbon cycle?

Conversion to agriculture or pasture land

Conversion to shifting cultivation

Abandoning agricultural or pasture land

Afforestation

What is shifting cultivation?

The process of growing crops in one place then moving, usually to protect soil quality.

Why do we need to alter ecosystems for carbon sequestration?

Diverse ecosystems sequester carbon better than e.g commercial forests

So we sometimes need to alter an area, e.g cut down trees, to diversify an ecosystem

This mimics how animals that are no longer present in the ecosystem would graze, for example

How do farming practises affect the fast carbon cycle?

Ploughing and harvesting release carbon from the pedosphere directly

Slash-and-burn techniques also directly release carbon

Regenerative farming, which aims to repair soil quality and nutrients, is now more common

How does shifting cultivation affect the fast carbon cycle?

In rainforests, there is often subsidence farming

Subsistence farming allows the ecosystem to regenerate, and thus encourages carbon sequestration

It works well on a small scale, but can cause issues on a larger scale

How does abandoning agricultural/pasture land effect the fast carbon cycle?

It can be good as it allows for rewilding

Can also cause mass decomposition- high carbon release

We can’t just abandon agricultural land, we must use the space to mimic the natural environment

How do tree plantations and afforestation effect the fast carbon cycle?

Palm oil plantations are very bad for the environment

Most tree plantations do not allow for the natural ecosystem to regenerate

What is done to turn forest into farmland?

Trees are removed by:

• cutting

• slash-and-burn

Tree stumps are removed

Soil is tested and prepared

What is done to turn wetlands into farmland?

• Soil is drained by lowering the water table

• The physical landscape may be altered so it doesn’t revert to wetland

• Vegetation is cleared

• The soil is usually amended

How is CO2 lost in the conversion of land to farmland?

The removal of trees and plants releases CO2 from biomass store

If trees are burned, release is sudden and large

Soil disturbance causes CO2 release from the pedosphere

What is the effect on the carbon cycle of putting livestock on the land?

Soil compaction

Methane and CO2 release

Soil disturbance leads to carbon release

Land degradation

What is tilling?

The process of turning over the top layer of soil, typically to prepare it for planting for gardening or agricultural purposes.

What happens to fields when not in use?

What gases are released through crop and livestock farming?

How might shifting cultivation be more damaging?

How might shifting cultivation be less damaging?

What will happen to shifting cultivation as population growth continues?

How might abandoning agricultural or pasture land be beneficial?

What could happen if agricultural land is not cleared properly?

How is afforestation a good thing?

How will the effects of afforestation vary around the world?