9.12.2a The Greenhouse Effect & Global Warming

SYLLABUS

Greenhouse gases in the atmosphere maintain temperatures on Earth high enough to support life.
Water vapour, carbon dioxide and methane are greenhouse gases.
Students should be able to describe the greenhouse effect in terms of the interaction of short and long wavelength radiation with matter.
Some human activities increase the amounts of greenhouse gases in the atmosphere. These include: • carbon dioxide • methane.
Students should be able to recall two human activities that increase the amounts of each of the greenhouse gases carbon dioxide and methane.
Based on peer-reviewed evidence, many scientists believe that human activities will cause the temperature of the Earth’s atmosphere to increase at the surface and that this will result in global climate change. However, it is difficult to model such complex systems as global climate change. This leads to simplified models, speculation and opinions presented in the media that may be based on only parts of the evidence and which may be biased.
An increase in average global temperature is a major cause of climate change. There are several potential effects of global climate change.
Students should be able to: • describe briefly four potential effects of global climate change • discuss the scale, risk and environmental implications of global climate change.
The carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.
The carbon footprint can be reduced by reducing emissions of carbon dioxide and methane.
Students should be able to: • describe actions to reduce emissions of carbon dioxide and methane • give reasons why actions may be limited.

What does this mean?

What is the Greenhouse Effect?

Without an atmosphere, Earth would have extremes of temperature.

The side facing the sun might be too hot for life.

The side facing away from the sun would be too cold for life because there would no gas to prevent the long wavelength heat from escaping.

The Greenhouse effect traps some heat to keep the planet warmer than it would be and warm enough for life to exist.

The Greenhouse Effect is a good thing!

How does it work?

The syllabus wants you to be able to explain in detail:

Short wavelength light energy can penetrate our planet's atmosphere. This is absorbed by the planet and heats it up during the day.
At night heat is emitted as longer waves (Heat/Infrared).
Some of this heat escapes back into space; some is absorbed by molecules of "Greenhouse Gases".
When the Greenhouse Gases re-emit the energy they emit some of it back down towards the Earth, stopping its escape.

It also expects you to know that the most important Greenhouse Gases are CO2 , water vapour and Methane.

Carbon Dioxide is not a very effective Greenhouse Gas but there is a lot more of it than most other Greenhouse gases and it is increasing.
Methane is much rarer but traps heat much more effectively than Carbon Dioxide

Where do Greenhouse Gases come from?

Water Vapour is in the air naturally but the worry is that if the Climate warms there will be more evaporation, causing higher levels of water vapour and more warming
Carbon Dioxide is also in the air naturally but increasing combustion of fuels means that it is rising rapidly and this is driving Global Warming.
Methane is produced from rotting material and from animal guts, scientists worry that too many farm animals are adding excess Methane and that existing warming is melting permafrost that has trapped Methane for millions of years - leading to ever increasing levels as more warming causes more melting.

In this graph, we can see that far more Carbon Dioxide is emitted than any other Greenhouse Gas.

This makes it that biggest threat even though it is not the most effective Greenhouse Gas

In this graph, we can see the main causes of Carbon Dioxide emissions.

All of them are caused by burning fuels for energy.

And 93% of them are from burning Fossil Fuels

Problems with Global Warming.

Learn a few problems associated with increased Global Warming:

1. Desertification - hot, arid parts of the world may get hotter and drier. Eventually, they may become desert

2. Flooding - Melting ice in Antarctica and Greenland will add water to the ocean, sea-level will rise and may flood low lying cities like London.

3. Extreme Weather - hurricanes are driven by the heat of the Sun. A hooter Earth will see more powerful storms.

Feedback loops - you don't need to learn these but Global Warming can lead to more Global Warming!

White Ice-caps reflect a lot of heat.
Melted ice-caps will expose rocks that absorb heat!
Permafrost melting releases Methane that causes more Heating.
A hotter Earth will see more evaporation - leading to more water vapour and more heating.
A hotter planet may have more forest fires - and these emit more Carbon Dioxide to trap more heat.

Carbon Footprint.

The Carbon Footprint of a product tries to measure the amount of Carbon Dioxide released to produce something we use.

eg. A cheap burger.

The cow that the burger is made from may be natural but feeding it will have required work that released Carbon Dioxide. eg Tractors release Carbon Dioxide ploughing and harvesting food for cattle,.
Transporting the cow to the slaughterhouse
Freezing/refrigerating the carcass.
Grinding the beef and making it into a burger.
Packaging had to be made.
The burger had to be frozen and transported.
Then it had to be cooked.
The bun is made from wheat but this needed tractors to sow seed and fertiliser had to be made and used to make them grow.
The wheat had to be harvested and transported.
The mill had to grind it.
The flour had to be transported and the bun had to be cooked.
Even the ketchup, the lettuce and the pickle that no one likes couldn't be produced without Carbon Dioxide being released.
And what if some or all the parts were brought from abroad!

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