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;
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 undergoing rapid changes.