• Each year, humans release more than 22 billion tonnes of carbon dioxide into the atmosphere through the burning of fossil fuels for energy.

• The plants, animals and micro-organisms around us are under threat from humans and their intrusions into the natural environment.

• Humans are adding large quantities of fine particles (aerosols) to the atmosphere, both from agricultural and industrial activities.

• Key human influences include changes in greenhouse gas concentrations, stratospheric ozone depletion, local air pollution and alterations in land use.

• In order to project the impact of human perturbations on the climate system, it is necessary to calculate the effects of all the key processes operating in the climate system.

• Even if the human emissions of greenhouse gases were to stop today, the global climate would keep changing for decades to come, due to the level of greenhouse gases currently in the atmosphere and the thermal inertia of the climate system.