A greenhouse gas (sometimes abbreviated GHG) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone. In the Solar System, the atmospheres of Venus, Mars, and Titan also contain gases that cause greenhouse effects. Greenhouse gases greatly affect the temperature of the Earth; without them, Earth's surface would be on average about 33 °C (59 °F) colder than at present.
Since the beginning of the Industrial Revolution, the burning of fossil fuels has contributed to the increase in carbon dioxide in the atmosphere from 280 ppm to 390 ppm, despite the uptake of a large portion of the emissions through various natural "sinks" involved in the carbon cycle. Anthropogenic carbon dioxide (CO2 ) emissions come from combustion of carbonaceous fuels, principally wood, coal, oil, and natural gas.
A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the stack, or chimney, effect. The space inside a chimney is called a flue. Chimneys may be found in buildings, steam locomotives and ships. In the United States, the term smokestack (colloquially, stack) is also used when referring to locomotive chimneys or ship chimneys, and the term funnel can also be used.
The height of chimneys plays a role in their ability to transfer flue gases using stack effect, the dispersion of pollutants at higher altitude helps to ease down its influence on surroundings. In the case of chemically aggressive output, the tall chimney allows partial or complete self-neutralization of chemicals in the air before they reach the ground. The dispersion of pollutants over greater area reduces their concentrations in compliance with regulatory limits.