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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Greenhouse Gases
Greenhouse gases play a crucial role in making Earth habitable, but human activities have increased their concentration to concerning levels. These gases trap heat in the atmosphere, causing global temperatures to rise in a process known as global warming.
Key Definitions:
The greenhouse effect is a natural process that warms Earth's surface. When the Sun's energy reaches Earth, some is reflected back to space, but greenhouse gases trap some of this heat. Without this natural process, Earth would be too cold for life (about -18°C instead of our average 15°C).
Human activities have increased greenhouse gas concentrations, enhancing the greenhouse effect. This traps more heat than necessary, causing global temperatures to rise. Since the Industrial Revolution, average global temperatures have increased by about 1.1°C.
Several gases contribute to the greenhouse effect, each with different sources and warming potentials.
Sources: Burning fossil fuels, deforestation, cement production
Lifespan: 300-1000 years
Most significant greenhouse gas due to its abundance and long atmospheric lifetime.
Sources: Livestock, rice paddies, landfills, fossil fuel extraction
Lifespan: About 12 years
25 times more potent than CO₂ at trapping heat over a 100-year period.
Sources: Agricultural fertilisers, burning fossil fuels, industrial processes
Lifespan: About 114 years
298 times more potent than CO₂ at trapping heat over a 100-year period.
While CO₂, methane and nitrous oxide are the most common greenhouse gases, others also contribute to global warming:
Human activities have significantly increased greenhouse gas concentrations since the Industrial Revolution. Understanding these sources is crucial for developing effective mitigation strategies.
The combustion of coal, oil and natural gas for electricity, heating and transportation releases large amounts of CO₂. This is the largest source of greenhouse gas emissions globally.
Example: A typical passenger vehicle emits about 4.6 tonnes of CO₂ per year.
Trees absorb CO₂ during photosynthesis. When forests are cleared for agriculture, logging, or development, this carbon sink is lost and stored carbon is released back into the atmosphere.
Example: Tropical deforestation accounts for about 10% of human greenhouse gas emissions.
Livestock produce methane during digestion (enteric fermentation), especially cattle and sheep. Rice paddies create anaerobic conditions where bacteria produce methane. Fertilisers release nitrous oxide.
Example: A single cow can produce up to 500 litres of methane per day.
Industrial processes like cement production release CO₂. Other industries release fluorinated gases and other potent greenhouse gases.
Example: Cement production accounts for about 8% of global CO₂ emissions.
The enhanced greenhouse effect is causing various environmental changes with far-reaching impacts on ecosystems and human societies.
Rising ocean temperatures and acidification are causing widespread coral bleaching. The Great Barrier Reef in Australia experienced major bleaching events in 2016, 2017 and 2020, affecting over 60% of the reef. When water temperatures rise, corals expel the algae living in their tissues, causing them to turn white and potentially die. This threatens marine biodiversity, as coral reefs support about 25% of all marine species despite covering less than 1% of the ocean floor.
Scientists use various methods to track greenhouse gas concentrations and understand their impact:
One of the most famous measurements of atmospheric CO₂ is the Keeling Curve, which shows continuous measurements taken at Mauna Loa Observatory in Hawaii since 1958. When measurements began, CO₂ levels were about 315 parts per million (ppm). Today, they exceed 415 ppm higher than at any point in at least 800,000 years based on ice core data.
Reducing greenhouse gas emissions requires action at individual, local, national and international levels.
The Paris Agreement is an international treaty adopted in 2015 with the goal of limiting global warming to well below 2°C, preferably 1.5°C, compared to pre-industrial levels. Countries submit their own climate action plans called Nationally Determined Contributions (NDCs). The agreement includes mechanisms for regular reporting and increasing ambition over time. As of 2023, 195 countries have signed the agreement, though current pledges are not yet sufficient to meet the temperature goals.
Greenhouse gases are essential for life on Earth through the natural greenhouse effect, but human activities have significantly increased their concentrations, leading to enhanced warming. The main greenhouse gases include carbon dioxide, methane and nitrous oxide, with sources ranging from fossil fuel combustion to agriculture and industrial processes.
The consequences of this enhanced greenhouse effect include rising temperatures, sea level rise, changing precipitation patterns and more extreme weather events. Addressing this challenge requires a combination of renewable energy adoption, changes in individual behaviour and policy measures at national and international levels.
Understanding greenhouse gases and their impacts is essential for making informed decisions about how we can contribute to mitigating climate change while adapting to its unavoidable effects.
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