Global warming is an increase in the temperature of the Earth's near-surface air. One main cause of global warming is the greenhouse effect, which was discovered by Joseph Fourier in 1824. The greenhouse effect is when absorption and emission of infrared radiation by atmospheric gases warm a planet's lower atmosphere and surface. Who is to blame for this? Us, humans, mankind.

The main pollutant gases produced are CO2, methane, tropospheric ozone, CFCs and nitrous oxide. CO2 concentrations are continuing to rise due to burning of fossil fuels and land-use change, which is deforestation. The burning of fosil fuels has produced three quarters of the increase of CO2 in the last 20 years due to human activity.

Aerosols and soot are another factor leading to global warming. Aerosols are produced by volcanic activity and emissions of pollutants such as sulfur dioxide. Soot may cool or warm, depending on whether it is airborne or deposited. Atmospheric soot aerosols directly absorb solar radiation, which heats the atmosphere and cools the surface.