Climate changeIB MYP Biology: Revision notes

The greenhouse effect is a natural process that keeps the Earth warm enough for life.

1. Radiation from the Sun passes through the atmosphere and warms the surface.
2. The warm surface gives out infrared radiation.
3. Greenhouse gases in the atmosphere absorb some of this infrared radiation and re-emit it in all directions, including back towards the surface.
4. Less heat escapes into space, so the Earth stays warmer.

Without it, the average temperature would be about -18 °C instead of about 15 °C.

• Carbon dioxide (CO₂): released by burning fossil fuels, respiration and deforestation. It is the most important because so much is released.
• Methane (CH₄): released from cattle and other farm animals, rice paddies, landfill sites and the extraction of natural gas. It absorbs more heat per molecule than CO₂ but there is much less of it.
• Water vapour and nitrous oxide are also greenhouse gases.

The enhanced greenhouse effect is the extra warming caused by human activities adding more of these gases.

• Burning fossil fuels (coal, oil, gas) for electricity, transport and industry releases carbon stored for millions of years as CO₂.
• Deforestation: fewer trees absorb CO₂ in photosynthesis, and the burning or rotting of trees releases CO₂.
• Farming: cattle and rice paddies release methane.
• Landfill: rotting waste releases methane.

CO₂ is now released faster than plants and oceans can absorb it, so its concentration rises: from about 280 ppm in 1800 to about 420 ppm in 2023.

As average temperatures rise (about 1.1 °C since 1850), there are many effects:

• Sea-level rise: ice caps and glaciers melt and the oceans expand as they warm, flooding coastal land.
• Extreme weather: more heatwaves, droughts, floods and storms.
• Habitat shifts: species move towards the poles or higher ground, and those that cannot move may die out. Coral reefs bleach.
• Farming is affected, as crops fail in some regions and grow better in others.

Mitigation means reducing the causes or the effects of climate change.

• Use renewable energy (wind, solar, hydroelectric) instead of fossil fuels.
• Improve energy efficiency in homes, transport and industry.
• Plant trees and stop deforestation, so more CO₂ is absorbed.
• Reduce the methane from farming and landfill, e.g. by capturing it, eating less beef and wasting less food.
• Use public transport and electric vehicles.
• International agreements, such as the Paris Agreement, set targets for cutting emissions.

Each has costs and benefits, such as expense, jobs and reliable supply.