Variations in solar energy - sunspot activity raises global temperature.
Volcanic eruptions - large quantities of volcanic dust in the atmosphere shield the Earth from incoming insolation, lowering global temperature. For example, the eruption of Mount Pinatubo in 1991 caused a dip in global temperatures.
Alternatively, some scientists would argue that large eruptions could exacerbate the green house effect and lead to global warming.
Milankovitch cycles or variations in the tilt and/or orbit of the Earth around the Sun (Wobble, roll and stretch theory).
Changing oceanic circulation such as the periodic warming (El Nino) and cooling (La Nina) of areas of the tropical Pacific Ocean.
Melting permafrost releasing large quantities of methane gas.
These physical causes of global temperature change have always existed and have been responsible for alternate heating and cooling cycles of the Earth's temperature in the past.
The video below shows a powerful volcanic eruption - a possible contributor to global warming.
The human causes of global warming have been in the news a lot in recent years and continued to cause much controversy. Developed countries currently use more energy, burn more fossil fuels and give off more greenhouse gases than developing countries.
Developing countries want to catch up with developed countries and this normally means using more energy and burning more fuel. Many of the human factors below are the result of growing population and economic development.
The burning of fossil fuels for transport, industry and power, producing carbon dioxide.
Worldwide deforestation, sometimes involving rainforest burning, which also produces carbon dioxide.
Car exhausts and nitrogen fertilisers, producing nitrous oxide.
CFCs found in fridges, air conditioning and aerosols and as a bi-product of the production of polystyrene packaging, like pizza and burger boxes.
Methane, produced from rice fields, landfill sites and from both ends of cattle.
Atom bomb testing.
Increasing industrialisation leading to air pollution.
Collectively, these physical and human causes have contributed to climate change.