Energy and environment are essential for sustainable development. The poor are disproportionately affected by environmental degradation and lack of access to clean, affordable energy services. These issues are also global as climate change, loss of biodiversity and ozone layer depletion cannot be addressed by countries acting alone.

Carbon Dioxide

60-90 percent of typical fossil fuels is chemically combined carbon. Burning them creates between 2 and 3.5 tonnes of carbon dioxide (CO2) per tonne of fuel. Because the carbon in fossil fuels has been locked up under ground for many millions of years, burning it increases the amount of CO2 in the atmosphere. Though natural processes do tend to absorb CO2, the overwhelming balance of scientific evidence indicates that burning fossil fuels at the present rate has already led to a significant increase in concentration of CO2 in the atmosphere. As more countries industrialise this effect will accelerate drastically unless there is a major reduction in the use of fossil fuels.

Sulphur and Nitrogen Oxides (SOx and NOx)

Coal and to some extent crude oil contain significant amounts of sulphur. When burned, this generates sulphur oxides, mainly sulphur dioxide (SO2) and a little sulphur trioxide (SO3), generically referred to as SOx. Both these gases are corrosive and toxic. At sufficient concentrations they cause serious health problems and even at lower levels they can contribute to acid rain which has already been seen to cause extensive damage to sensitive forests and lakes.

Nitrogen oxides (generically known as NOx) are also formed by combustion of fuels. They result both from nitrogen in the fuel (eg coal) and nitrogen in the air. Again these compounds are harmful to health and contribute to acid rain.

Particulates and heavy metals Combustion of most fossil fuels (less so natural gas) results in some solid wastes including:

   Soot and solid organic (carbon containing) compounds resulting from incomplete combustion,
   Mineral residues and metal compounds including heavy metals.

These materials appear in smoke, dust and ash. Most of them are toxic or harmful to health in one way or another and solid residues can create disposal problems.

Other harmful emissions

Incomplete combustion of fuel results in other harmful emissions eg unburned hydrocarbons, carbon monoxide and other by-products. It also leads to additional disposal problems with unburned matter adding to the amount of ash from solid fuel furnaces. Where combustible wastes are being burned as part of the fuel, it is particularly important to achieve complete combustion in order to avoid formation of highly toxic by-products eg dioxins.

Atmospheric chemistry is complex and there are several forms of air pollution that are the result of further reaction in the atmosphere of fuel derived substances, photochemical smog being a well known example.