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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Human Activities and Emissions
Humans have dramatically altered Earth's atmosphere through various activities that release greenhouse gases. These emissions trap heat in our atmosphere, leading to global climate change. Understanding the sources and impacts of these emissions is crucial for developing solutions.
Key Definitions:
Carbon dioxide (CO₂): Released by burning fossil fuels, deforestation and industrial processes. Stays in the atmosphere for hundreds of years.
Methane (CH₄): Released from livestock, rice paddies, landfills and natural gas extraction. 25 times more potent than CO₂ over 100 years.
Nitrous oxide (N₂O): Released from fertilisers, burning fossil fuels and industrial processes. 298 times more potent than CO₂.
Energy production: 35% of global emissions
Industry: 21% of global emissions
Agriculture and land use: 24% of global emissions
Transport: 14% of global emissions
Buildings: 6% of global emissions
Burning fossil fuels (coal, oil and natural gas) for energy is the largest source of human-caused CO₂ emissions. These fuels power our homes, industries and vehicles but release carbon that was locked away underground for millions of years.
Coal and natural gas power plants produce about 25% of global emissions. A single coal power station can emit several million tonnes of CO₂ annually.
Cars, trucks, ships and planes rely heavily on petroleum fuels. The average car produces about 4.6 tonnes of CO₂ per year.
Manufacturing, cement production and steel making require enormous energy inputs, often from fossil fuels.
The UK has dramatically reduced coal use in electricity generation. In 2012, coal provided 39% of UK electricity. By 2020, this had fallen to less than 2%, with renewable energy sources like wind and solar increasing to over 40%. This shift has helped the UK reduce carbon emissions from electricity by nearly 70% in a decade.
Trees and plants absorb CO₂ during photosynthesis, acting as carbon sinks. When forests are cleared for agriculture, timber, or development, this stored carbon is released back into the atmosphere.
Around 10% of global greenhouse gas emissions come from deforestation and land use change. Tropical forests are particularly important carbon stores, with the Amazon rainforest alone storing an estimated 123 billion tonnes of carbon.
Forests normally act as carbon sinks, absorbing more CO₂ than they release. Deforestation reverses this process, turning forests into carbon sources. When trees are cut down and burned or left to rot, the carbon they've stored is released as CO₂.
A mature tree can absorb about 22 kg of CO₂ per year. Clearing one hectare of tropical forest can release 400-500 tonnes of carbon.
Agriculture: Clearing land for cattle ranching and growing crops like soya and palm oil is the leading cause of deforestation.
Timber: Logging for wood products removes carbon-storing trees.
Development: Urban expansion and infrastructure projects often require forest clearing.
Mining: Extracting minerals and metals can lead to significant forest loss.
Modern agriculture contributes significantly to greenhouse gas emissions through various practices and processes.
Cattle and sheep produce methane during digestion (enteric fermentation). A single cow can produce up to 500 litres of methane per day. Livestock manure also releases methane and nitrous oxide.
Flooded rice paddies create anaerobic conditions where bacteria produce methane. Rice cultivation accounts for about 10% of agricultural methane emissions.
Nitrogen fertilisers release nitrous oxide when broken down in soil. Over-application leads to higher emissions and water pollution.
The global livestock industry produces more greenhouse gas emissions than all cars, planes, trains and ships combined. There are approximately 1.5 billion cattle worldwide, each producing significant methane emissions. Scientists are researching feed additives that can reduce methane production in cattle by up to 30% and some farmers are implementing rotational grazing practices that can help soil store more carbon.
Beyond energy use, certain industrial processes directly release greenhouse gases as part of chemical reactions.
Some industrial processes would produce emissions even if they used 100% renewable energy because the emissions come from chemical reactions, not just energy use.
Making cement requires heating limestone (calcium carbonate), which releases CO₂ as a byproduct. Cement production accounts for about 8% of global CO₂ emissions.
For every tonne of cement produced, about 900 kg of CO₂ is released.
Steel production requires coal not just for energy but as part of the chemical process to remove oxygen from iron ore.
Aluminium production releases perfluorocarbons (PFCs), extremely potent greenhouse gases with warming potentials thousands of times greater than CO₂.
How we handle waste significantly impacts greenhouse gas emissions, particularly methane from organic waste decomposition.
When organic waste decomposes in landfills without oxygen (anaerobically), it produces methane. Modern waste management can either reduce these emissions or capture them for energy.
Recycling: Reduces the need for new materials and the emissions from their production.
Composting: Allows organic waste to decompose aerobically, producing CO₂ instead of methane (which is 25 times more potent).
Waste-to-energy: Capturing methane from landfills or sewage treatment to generate electricity.
The average UK person produces about 400kg of waste annually.
Recycling one tonne of paper saves about 17 trees and 4,000 kWh of electricity.
Food waste is responsible for about 8% of global greenhouse gas emissions.
Understanding the sources of emissions helps us identify effective solutions. Many technologies and practices already exist to reduce our impact.
Shifting from fossil fuels to renewable energy sources like wind, solar and hydropower. Improving energy efficiency in buildings, transport and industry.
Protecting and restoring forests, wetlands and grasslands that absorb carbon. Implementing sustainable farming practices that build soil carbon.
Developing new technologies for carbon capture, zero-carbon cement and sustainable aviation fuels. Creating plant-based alternatives to high-emission foods.
While systemic change is essential, individual choices matter too. The average UK person's carbon footprint is about 10 tonnes of CO₂ per year. Simple actions like eating less meat (especially beef), reducing food waste, walking or cycling for short journeys and improving home insulation can significantly reduce your personal emissions. For example, switching to a plant-based diet can reduce food-related emissions by up to 70%.
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