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examBoard: Cambridge
examType: IGCSE
lessonTitle: Human Influence on Climate
Humans have been changing Earth's climate since the Industrial Revolution began around 250 years ago. Our activities release greenhouse gases that trap heat in the atmosphere, causing global temperatures to rise faster than at any time in Earth's recent history.
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 while the rest is absorbed and re-radiated as heat. Greenhouse gases trap this heat in the atmosphere, like a greenhouse traps heat inside. Human activities have increased these gases, enhancing the greenhouse effect and causing global warming.
"Global warming" refers specifically to the long-term heating of Earth's climate system due to human activities. "Climate change" includes global warming but also refers to the broader range of changes happening to our planet, including rising sea levels, shrinking mountain glaciers and shifts in flower/plant blooming times.
The biggest contributor to climate change is burning fossil fuels like coal, oil and natural gas for electricity, heat and transportation. When burned, these fuels release carbon dioxide (CO₂) and other greenhouse gases into the atmosphere.
Cars, trucks, ships and planes burn fuel and produce about 14% of global greenhouse gas emissions. A typical passenger vehicle emits about 4.6 tonnes of CO₂ per year.
Generating electricity and heat by burning fossil fuels causes about 25% of global emissions. Coal-burning power plants are especially carbon-intensive.
Heating, cooling and powering buildings accounts for approximately 6% of global emissions, mainly from burning fossil fuels for heating and cooking.
Trees absorb CO₂ from the atmosphere through photosynthesis. When forests are cut down or burned, this stored carbon is released back into the atmosphere as CO₂. Additionally, fewer trees mean less CO₂ is removed from the atmosphere.
The Amazon rainforest, often called "Earth's lungs," absorbs millions of tonnes of CO₂ each year. Since 1978, over 750,000 square kilometres of Amazon rainforest have been destroyed an area larger than France. This deforestation releases stored carbon and reduces the forest's capacity to absorb CO₂. In 2019 alone, Brazil lost 1.7 million hectares of primary forest. The main causes are clearing land for cattle ranching, soy production and logging. This deforestation contributes approximately 1.5% of global greenhouse gas emissions annually.
Agriculture contributes to climate change in several important ways:
Cows and sheep produce methane during digestion. Methane is a greenhouse gas 25 times more potent than CO₂ at trapping heat in the atmosphere. Livestock farming contributes about 14.5% of global greenhouse gas emissions. A single cow can produce up to 500 litres of methane per day!
Flooded rice fields create oxygen-free conditions where bacteria produce methane. Rice cultivation is responsible for approximately 1.5% of global greenhouse gas emissions. As rice feeds half the world's population, this is a significant challenge.
Additionally, fertilisers used in farming release nitrous oxide, another powerful greenhouse gas that is 298 times more effective at trapping heat than CO₂.
Many industrial processes release greenhouse gases:
When organic waste decomposes in landfills without oxygen, it produces methane. Wastewater treatment can also release methane and nitrous oxide. Globally, waste management accounts for about 3% of greenhouse gas emissions.
China is currently the world's largest emitter of greenhouse gases, responsible for approximately 27% of global emissions. This is largely due to its rapid industrialisation and heavy reliance on coal for energy. In 2018, China's CO₂ emissions reached 10 billion tonnes. However, on a per-person basis, China's emissions (7.4 tonnes per person) are still lower than those of countries like the United States (16.2 tonnes per person). China has begun addressing this issue with massive investments in renewable energy, now leading the world in solar panel and wind turbine production.
Scientists use several methods to measure human impact on climate:
CO₂ levels are measured in parts per million (ppm). Pre-industrial levels were about 280 ppm. Today, they exceed 415 ppm a 48% increase.
Earth's average temperature has increased by about 1.1°C since pre-industrial times. This may seem small, but it represents a massive amount of added heat energy.
Global sea levels have risen about 20cm since 1900, with the rate accelerating. This is due to melting ice and thermal expansion of seawater as it warms.
There are many ways humans can reduce their impact on the climate:
Transitioning from fossil fuels to renewable energy sources like solar, wind and hydropower can significantly reduce emissions. The cost of renewable energy has fallen dramatically in recent years, making it increasingly competitive with fossil fuels.
Using public transport, cycling, walking, carpooling and switching to electric vehicles can reduce transport emissions. Many countries are now planning to phase out petrol and diesel vehicles in the coming decades.
Planting trees and protecting existing forests helps absorb CO₂ from the atmosphere. Large-scale reforestation projects are underway in many countries, with ambitious targets to plant billions of trees.
Reducing consumption of meat, especially beef, can lower emissions from agriculture. Plant-based diets typically have a much lower carbon footprint than meat-heavy diets.
The UK has made significant progress in reducing its greenhouse gas emissions. Between 1990 and 2019, UK emissions fell by 44%, while the economy grew by 78%. This was achieved through several measures:
Human activities are the main driver of current climate change, primarily through:
Understanding these human influences is essential for developing effective strategies to mitigate climate change. While the challenge is significant, there are many solutions available that can help reduce our impact on the climate while also providing economic and health benefits.
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