Green House Gases
Glass covering greenhouses admits light and heat energy but blocks some of the infrared heat energy that is radiated back. When the sun shines the green house becomes warmer than the external environment. In the atmosphere, a similar effect occurs. Greenhouse gases are carbon dioxide, methane, nitrous oxide and chlorofluorocarbons (CFCs). These gases act like the glass covering a greenhouse, letting sunlight in but blocking some of the infrared radiation from the earth's surface that carries heat back into space.
The gases act like a blanket wherever their concentration increases. Local concentrations increase local heat and increased differences between hotter and colder regions drives weather events into more extreme ranges.
Global warming means that the earth retains more of the sun's heat over time. The warming effect of greenhouse gases is reduced by particle pollution and clouds that block incoming infrared radiation. Without particle pollution, global warming would be more obvious.
Carbon dioxide is the most important greenhouse gas, produced by burning of fossil fuels, and other organic matter. The concentration of CO2 was 280 PPM before the industrial revolution and now is over 350 PPM. High emission countries pump produce 3 metric tons of carbon dioxide per person, but the US produces 5.2 metric tons per person. Low emission countries produce less than 1 metric ton per capita. Most of Africa, South America, and Asia are below 1 metric ton.
In the 1990s, the US produced 23% of global CO2 emissions, Western Europe 14%, former Soviet bloc 20 %, China 12%, India 4% and Japan 5%. If you include Brazil, Indonesia and Germany in the list of major polluters, the total group accounts for 56 % of the world's population, 59% if its economic output, 58% of its carbon-dioxide emissions and 53% of its forests.
Methane is less abundant but traps more heat than carbon dioxide. Methane emissions are about 550 million tons per year from biomass decomposition in wetlands, rice farming, ruminant animals and landfills. Methane is "natural gas" and some enters the atmosphere during its commercial distribution and use as a fuel. Large reservoirs of methane also are found in the arctic and in marine sediments, as methane hydrates. Each methane molecule is encased by water ice molecules. There is speculation that ice-bound methane may be released as ocean temperatures rise and further accelerate global warming.
Nitrogen oxides, like hydrocarbons, are precursors to the formation of ozone and contribute to acid rain. Catalytic converters in car exhaust systems break down heavier nitrogen gases, forming nitrous oxide (NO2) - 300 times more potent than carbon dioxide as a greenhouse gas. Nitrous oxide makes up about 7.2 percent of the gases that cause global warming. Vehicles with catalytic converters produced nearly half of that nitrous oxide. Nitrous oxide also comes from nitrogen-based fertilizers and manure from farm animals.
Hydrofluorocarbon chemicals (HFCs) Refrigerants designed to protect the ozone layer have become a major contributor to global warming. Hydrofluorocarbon chemicals (HFCs) were developed to phase out ozone-depleting gases but they are more potent than carbon dioxide as greenhouse gases. A study at the Netherlands Environmental Assessment Agency suggested that HFC emissions will have the heat trapping effect up to 8.8 billion tonnes of carbon dioxide annually by 2010. (G. J. M. Velders et al. Proc. Natl Acad. Sci. USA doi:10.1073.pnas.0902817106; 2009).
The reduction in forest biomass and the exposure of ocean plankton to increase UV radiation are also concerns. Ocean phytoplankton supplies up to 70% of the oxygen we breathe. The planet's thermostat had been set at a pleasant average temperature of 59 degrees (F) for the last 10 thousand years or so and is now poised to undergo a rapid change.