Contains the full lesson along with a supporting toolkit, including teachers’ notes.
The atmosphere contains a number of gases that trap some of the heat radiated from the Earth’s surface and keep the planet about 33 °C warmer than it would otherwise be. Without this ‘greenhouse effect’ the Earth would be a frozen wasteland with an average temperature of about −18 °C and life as we know it would be impossible.
The main greenhouse gases are, in order of their contribution to global warming, water vapour, carbon dioxide (CO2), nitrous oxide (N2O), tropospheric ozone (O3) and methane (CH4). (The water content of the atmosphere cannot be directly changed; it is dependent on the average global temperature and cannot be changed directly.)
Since the beginning of the industrial revolution (ca. 1750) human activity has added to the natural levels of these gases, causing an enhanced greenhouse effect. The global population has risen from less than 1 billion to 7 billion; urbanisation has gone from less than 10% to over 50%. Global energy consumption is now more than 25 times greater than it was in 1750.
Atmospheric CO2 can be reduced in a number of ways including:
Some of the techniques to reduce atmospheric CO2 that are currently being tested are outlined below.
Carbon capture and storage (CCS)
The term ‘carbon capture’ refers to processes in which CO2 is captured at source with a view to storing it permanently. Anthropogenic CO2 largely comes from fuel combustion and so CCS research has focused on:
• Post-combustion capture
• Pre-combustion capture
Post-combustion capture refers to the extraction of CO2 from the flue gases of power stations and other large facilities that involve combustion.