Human activities increase the greenhouse gases that naturally occur in the atmosphere.
Fuel combustion is the chief source of rising CO2 concentrations.
Ranching, farming and landfills have raised methane levels.
These human activities magnify the warming effects of the greenhouse gasses.
Aerosols, smoke and sulphate polution from industry, can reflect sunlight, and have a cooling effect.
Whilst not a human effect, the volcanic eruption of Mt Pinatubo in 1991 blew a colossal amount of sulphates into the stratosphere, causing a worldwide drop in temperature that lasted two years.
