P2.3 What is the evidence for global warming, why might it be occurring, and how serious a threat it is?
The sun emits electromagnetic radiation with a principle frequency that increases with temperature – the Earth is surrounded by an atmosphere that allows some of the electromagnetic radiation emitted by the Sun to pass through.
The Earth emits electromagnetic radiation into space –this radiation has a lower principle frequency than that emitted by the Sun – There are gases in the atmosphere that absorb or reflect some of this radiation. This keeps the Earth warmer than it would otherwise be and is known as the GREENHOUSE EFFECT.
Two of the ‘greenhouse gases’ which keep the Earth warm are CARBON DIOXIDE (CO2) and METHANE (CH4). Both of the gases contain CARBON however there’s a fairly small amount of CO2 and just traces of CH4 on Earth.
The carbon cycle is an example of a balance system:
❶ Carbon dioxide is removed from the atmosphere by green
plants to produce glucose by photosynthesis
❷ The carbon obtained by photosynthesis is used to make carbohydrates, fats and proteins in plants.
❸ Animals respire, releasing carbon dioxide into the atmosphere
❹ When plants and animals die, other animals and microorganisms feed on their bodies, causing them to break down. Excretion also releases carbon
❺ As the detritus feeders and microorganisms eat the dead plants and animals, they respire, releasing carbon dioxide into the atmosphere.
The carbon cycle can be used to explain several points
- The amount of carbon dioxide in the atmosphere had remained roughly constant for thousands of years because it was constantly being recycled by plants and animals
- The importance of decomposers, which are microorganisms that break down dead material and release carbon dioxide back into the atmosphere
- The amount of carbon dioxide in atmosphere has been steadily increasing over the last 200 years, largely due to human activity such as burning fossil fuels and deforestation.
- Fossil fuels contain carbon that was removed from the atmosphere millions of years ago and has been ‘locked up’ ever since. Burning fossil fuels for energy releases this carbon into the atmosphere
- Burning forests (deforestation) to clear land not only releases the carbon they contain but also reduces the number of plants removing carbon dioxide from the atmosphere
Global warming could result in:
- It being impossible to continue growing some food crops in particular regions because of climate change
- More extreme weather conditions, due to increased convection and larger amounts f water vapour in the hotter atmosphere
- Flooding of low lying land due to rising sea levels caused by melting continental ice and expansion of water in the oceans
Climatologists collect data about how the Earth’s temperature has changed over the years. The data collected is used with climate models to look for patterns. These computer models show that one of the main factors causing global warming is from human activities.