Climate Change Mitigation (AQA A-Level Geography): Revision Notes

Climate change mitigation

Introduction to climate change mitigation

The Earth's climate is changing due to human activities that release greenhouse gases into the atmosphere. When we talk about climate change, we need to understand a key concept called radiative forcing.

Radiative forcing is the imbalance between incoming solar energy and outgoing infrared energy from Earth's surface. It is measured in watts per square metre ($\text{W/m}^2$).

When this energy balance is disrupted, the planet either warms up or cools down. Before 1750, radiative forcing was negligible. However, since the Industrial Revolution, it has increased significantly due to greenhouse gas emissions and changes in land use that affect the Earth's reflectivity (albedo).

Water and carbon cycles and the atmosphere

The relationship between water and carbon cycles creates a complex system that amplifies global warming through positive feedback mechanisms.

Carbon dioxide plays a crucial role in Earth's climate system. Whilst CO₂ contributes approximately 20% to the overall greenhouse effect, and water vapour accounts for about 50%, it is actually CO₂ that controls the temperature. This is because carbon dioxide levels determine how much water vapour can remain in the atmosphere, which in turn determines the magnitude of the enhanced greenhouse effect.

The positive feedback loop

When carbon dioxide concentrations increase in the atmosphere, several interconnected processes occur:

• Air temperatures rise due to enhanced greenhouse heating
• Oceans warm up as a result
• Warmer ocean water evaporates more readily, releasing additional water vapour into the atmosphere
• Water vapour itself is a powerful greenhouse gas, so this amplifies the warming effect
• Higher temperatures also warm the tundra regions
• Warming tundra releases both methane (CH₄) and additional CO₂ that were previously locked in frozen soils
• These extra greenhouse gases further increase atmospheric temperatures
• Warmer oceans become less able to dissolve CO₂, releasing previously dissolved carbon dioxide back into the atmosphere

Climate change mitigation strategies

Climate change mitigation refers to efforts aimed at reducing or preventing greenhouse gas emissions. There are numerous approaches to achieving this goal, which can be organised into several main categories.

The mitigation strategies include:

Energy production

• Transitioning to renewable energy sources (wave and tidal power, wind power, solar energy)
• Increasing the use of nuclear energy
• Implementing carbon storage and capture (CCS) technologies

Transport and aviation

• Improving vehicle fuel efficiency
• Developing sustainable urban transport systems
• Shortening flight times through efficient air traffic control
• Changing routes to reduce contrail formation
• Enhancing fuel efficiency in the aviation sector

Urban design

• Implementing better building design with improved insulation and ventilation
• Installing green roofs
• Improving waste management practices, including recycling and capturing landfill gas

Rural land use

• Changing agricultural methods (such as adopting non-ploughing techniques)
• Implementing afforestation and reforestation programmes (silviculture)

Each of these strategies contributes to reducing overall greenhouse gas emissions, though they operate through different mechanisms and at different scales.

Carbon capture and sequestration (CCS) technologies

Carbon capture and storage represents a technological approach to preventing CO₂ from entering the atmosphere. This method can capture up to 90% of carbon dioxide emissions produced from fossil fuel use in electricity generation and industrial processes.

How CCS works

The CCS process consists of three main stages:

1. Capturing the CO₂

Technologies allow the separation of carbon dioxide from gases produced during electricity generation and industrial processes. There are three main methods:

• Pre-combustion capture
• Post-combustion capture
• Oxy-fuel combustion

2. Transporting the CO₂

Once captured, millions of tonnes of carbon dioxide are transported to storage locations. This is typically done through:

• Pipelines
• Ship transport
• Road tankers

3. Storing the carbon dioxide

The captured CO₂ must be stored securely to prevent it from entering the atmosphere. Storage options include:

• Depleted oil and gas reservoirs
• Deep saline aquifer formations (several kilometres below the surface)
• Deep ocean storage

Geo-sequestration

When carbon dioxide is stored in deep geological formations, the process is called geo-sequestration. The CO₂ is converted into a high-pressure, liquid-like form known as 'supercritical CO₂', which behaves like a runny liquid. This supercritical CO₂ is injected directly into sedimentary rocks.

Suitable geological storage sites include:

• Old oil fields
• Gas fields
• Saline formations (underground salty water layers)
• Thin coal seams

Enhanced oil recovery

CCS systems can extract a greater percentage of oil and gas from existing reservoirs. The CO₂ is injected under pressure, which helps force the remaining oil or gas out. Whilst this helps pay for the CCS technology through increased oil production, it does create a problem by producing more fossil fuel for eventual burning.

Ocean storage

Carbon dioxide could also be stored in the ocean through various methods, though this approach has significant disadvantages due to ocean acidification and associated environmental problems.

Case study: Boundary Dam CCS plant

The Boundary Dam facility in Saskatchewan, Canada, provides a real-world example of CCS technology in operation. Built by the provincial utility SaskPower, this coal-fired power station has been retrofitted to capture carbon emissions.

Costs and benefits

Changing rural land use

Carbon storage can be improved in rural areas by ensuring that carbon inputs to the soil exceed carbon losses. Various strategies can be employed depending on land use, soil properties, climate conditions, and the size of the land area.

Grasslands

Grasslands offer substantial potential for greenhouse gas mitigation, with an estimated 810 million tonnes of CO₂ potentially being sequestered globally per year (in the period to 2030), with almost all of this carbon being stored in the soil.

Improving carbon storage in grasslands

• Avoiding overstocking: Too many grazing animals can damage grasslands and reduce their carbon storage capacity
• Adding manures and fertilisers: These materials have a direct impact on soil organic carbon (SOC) levels by increasing the added organic material. They also provide indirect benefits by boosting plant productivity and stimulating soil biodiversity (for example, earthworms help degrade and mix organic material into the soil)
• Revegetation: Using improved pasture species and legumes can increase productivity, resulting in more plant litter and underground biomass, which adds to the SOC stock
• Irrigation and water management: Better water availability improves plant productivity and increases the production of soil organic matter

Croplands

Agricultural lands also offer opportunities to increase soil organic carbon through various techniques:

• Mulching: This practice adds organic matter to the soil. When crop residues are used as mulch, it also prevents carbon losses from the system
• Reduced or no tillage: Ploughing and harrowing accelerate the decomposition of organic matter and release soil carbon that might otherwise remain stored. Reduced tillage also prevents the break-up of soil aggregates that protect carbon
• Some use of animal manure or chemical fertilisers: These can increase plant productivity and therefore SOC levels
• Rotations of cash crops: Using pasture or cover crops alongside cash crops, and applying green manures, can increase the biomass returned to the soil
• Using improved crop varieties: These produce higher productivity both above and below ground, enhancing crop residues and increasing SOC
• Trees in croplands (silviculture) and orchards: These can store carbon both above and below ground. CO₂ emissions can be further reduced if the trees are cultivated as a renewable source of fuel

Forests and tree crops

Forests play a vital role in reducing atmospheric CO₂ by storing large quantities of carbon both above and below ground.

• Protection of existing forests: Preserving current forests maintains their soil carbon stocks
• Reforesting degraded lands: Increasing tree density in degraded forests raises biomass density and therefore carbon density, both above and below ground

Improved aviation practices

The aviation industry is a significant and growing source of CO₂ emissions. According to the Air Transport Action Group, in 2019 the global aviation industry carried 4.5 billion passengers, producing 915 million tonnes of CO₂.

Whilst the industry has made considerable progress in reducing its CO₂ production (for example, modern aircraft like the Airbus A380 and Boeing 787 use less than three litres of fuel per 100 passenger kilometres), the EU Directorate General for Climate Action warns that global CO₂ emissions from aviation will be 70% higher in 2020 than in 2005 and could increase by a further 300% by 2050.

The diagram above shows various ways the aviation industry could reduce emissions. These must be approached cautiously as many remain at the aspirational or theoretical stage.

Movement management strategies

Design and technology innovations

• Increased engine efficiency
• Increased use of biofuels (sustainable aviation fuels)
• Improved aerodynamics
• Reduced weight of aircraft and engines
• Carbon capture within the engines themselves
• Maximising the number of seats per aircraft

Remember!