Milankovitch Cycles

Axial Tilt
The less the tilt the less the variation in Summer and Winter temperatures.
This will make Summers less warm and will encourage snow to last longer forming glacial ice.
Occurs over 41,000 years.

Variation in Volcanic Activity

Volcanic eruptions which produce a large amount of Sulphur Dioxide into the upper atmosphere (Stratosphere) can lead to global cooling, as the gases reflect and absorb more insolation from the sun before it gets to the Earth.
This makes the Earth cooler as has been seen after modern day volcanic eruptions, such as Krakatau, in the past much larger volcanoes had a larger effect. 

https://www.nasa.gov/topics/earth/features/stratospheric-aerosols.html

Powerful volcanic eruptions - National 5 Geography - BBC Bitesize

Variation in Ice Caps

Ice cap melting: Melting of ice caps releases additional fresh water into the oceans, which in turn alters ocean circulation with cold and warm ocean currents being affected.
This also reduces the albedo effect as there is less energy being reflected as more land is exposed.

Permafrost melting: As permafrost melts within the Arctic tundra, frozen organic matter starts to decay releasing Methane. 

Global Climate Change 1

Explain the physical factors affecting climate change.
8

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Human Causes

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The Greenhouse Effect

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Some gases in the Earth’s atmosphere stop heat radiating into space from the Earth. This is called the greenhouse effect and the gases involved are called greenhouse gases. 
Radiation from the Sun passes through the Earth’s atmosphere.
The Earth absorbs radiation with short wavelengths and so warms up. Heat is radiated from the Earth as longer wavelength infrared radiation.
Some of this infrared radiation is absorbed by greenhouse gases in the atmosphere.
The atmosphere warms up.

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The Enhanced Greenhouse Effect

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Human activities are causing the release of large amounts of Greenhouse gases, particularly carbon dioxide. 
As the percentage of carbon dioxide in the atmosphere has increased, so in general has the Earth’s mean temperature.

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The Greenhouse Effect

Global Warming

Human Cause - Greenhouse Gases

Carbon Dioxide (CO₂)

Methane (CH₄)

Nitrous Oxides (N₂O)

Chlorofluorocarbons (CFC’s)

Hydrofluorocarbons (HFC’s)

Sulphur hexafluoride (SF₆)

There are 6 main Greenhouses gases, but the most important ones are the first three.
The amount of these gases have all been increasing in our atmosphere due to human factors.

Carbon Dioxide (CO₂)

Burning fossil fuels, for example coal, oil and natural gas release Carbon Dioxide into the atmosphere. These has been used increasingly to generate electricity in power stations and to heat homes.

Deforestation, especially in the Amazon Rainforest, has resulted in more carbon dioxide being released when trees are burnt.

With fewer trees there is less photosynthesis so less CO² is captured by vegetation. 

Methane (CH₄)

21 times as effective in trapping heat than CO2.

Methane is produced when organic material is broken down anaerobically, without oxygen. This can happen in the following ways:

In landfill sites as waste / vegetation decomposes.
In padi fields when the rice plants are left to rot after they have been harvested.
In the stomachs of cows as they digest grass and then released as they belch and fart.
When permafrost melts the methane trapped in the ground for thousands of years can continue to biodegrade and is able to escape into the atmosphere. 

Nitrous Oxides (N₂O)

310 times more effective in trapping heat than Carbon Dioxide. 

The largest source is agriculture and the majority of agricultural emissions result from nitrogen fertilisers of agricultural soils (87 percent of the agriculture total). When too much nitrogen feritsier is put on the farmland it can react with the rain and atmosphere and turn into nitrous oxide.

Nitrous Oxide is also released from vehicles especially diesel cars / lorries.