Wx Savvy | Climate

What Are The Greenhouse Gases?

A greenhouse gas is any gas that absorbs heat energy and thus helps keep earth warm enough to sustain life (see Greenhouse Effect for background info).

What actually happens is that the gas molecule in the air will absorb longwave radiation coming from the land or ocean. Then the molecule will radiate it's own heat energy which will likely be absorbed by another greenhouse gas molecule (1). This cycle keeps heat energy near the surface of earth and allows our global temperatures to sustain life.

Some greenhouse gases are more effective at trapping heat then others and most are naturally occurring. However humans can alter the natural levels through car emissions and power plant emissions.

Carbon Dioxide- CO₂

Carbon dioxide represents about .038% of our atmosphere. Carbon dioxide occurs naturally and is also removed naturally. For example, trees will take CO2 out of the air and use it for photosynthesis and oceans will absorb CO2. This is all part of the global carbon cycle. Some CO2 is naturally added to the atmosphere while some is naturally removed. It is estimated that humans have increased the amount of carbon dioxide in the air by 5% (2).

Carbon dioxide from humans comes as a byproduct of burning fossil fuels like Coal, Oil, and Natural Gas, which all provide us with energy. In fact, about 70-90% of human emitted carbon dioxide is a direct result of using fossil fuels (2).

Although not the most effective absorber of heat compared to other greenhouse gasses, carbon dioxide is one of the most plentiful greenhouse gases. Carbon dioxide levels in the atmosphere have increased about 31% since the industrial revolution(2). Carbon dioxide is also in your car's exhaust, and by the way there are over 600 million cars in the world today. Many people want to curb our emissions of carbon dioxide because they think it is a primary cause of global warming. Others aren't sure and don't want to risk the negative effect on our economy because carbon dioxide is tied so closely to energy and fuel.

Methane- CH₄

Methane is another greenhouse gas which has more than doubled in the past 200 years⁽²⁾. Methane can result from gas escaping from decaying bacteria like the waste found in our landfills. It is also released from the production and transportation of coal, natural gas and oil. Methane is also a byproduct of rice patties and incomplete fossil fuel combustion.

Ozone- O₃

It's important to realize that the ozone hole is not caused by global warming and global warming is not caused by the ozone hole. They are two separate issues. In fact, they're two separate layers of the atmosphere, one is high up and good for us, the other is near the surface and bad for us.

The ozone hole is caused by a seasonal depletion of ozone way high up in the atmosphere. The ozone high up in the stratosphere helps limit the amount of damaging UV sunlight that reaches earth. However, what we're talking about here is ozone near the surface that is aiding in warming the planet.

Excessive levels of ozone at the surface occur on days of intense heat as the sun's radiation reacts with nitrogen oxides from industrial emissions and car exhaust to form the chemical called ozone.

Ozone is also a poisonous gas and can cause heart attack symptoms, breathing problems, and can be fatal in some cases. This is why on "ozone action" days most people should try to stay indoors and limit physical activity. Children, elderly and those with respiratory problems are most at risk when ozone levels get too high.

Ozone also helps to form smog in urban areas. So next time someone is talking about saving the ozone layer, ask them "which layer do you want to save?" . Then you can inform them on the hazards of low-level ozone.

Nitrous Oxide- N₂O

Nitrous oxide added to our atmosphere results from the use of nitrogen based fertilizers, widely used by farmers, from human waste as it is released during decay, and most important from car exhaust. Nitrous oxide is 200 times more effective of a heat trapper than carbon dioxide, though nitrous oxide much less prominent in our atmosphere compared to carbon dioxide. N2O levels are up 15% in last 250 years.

Water Vapor- H₂0
Water in vapor form is the best heat trapper of them all! In fact, it traps heat much better than all the greenhouse gasses combined! However, there is a catch. Water vapor does not stay in the atmosphere as long as the other greenhouse gases. As the hydrological cycle describes, water is constantly being recycled from rivers to oceans to water vapor to raining or snow and back into the rivers again. Thus, the amount of this greenhouse gas in our atmosphere is constantly changing, whereas other greenhouse gases stay in the atmosphere for a long time.

Remember, most of these gases are all naturally present in our atmosphere, without which we wouldn't be here. The debate over greenhouse gases focuses on if we are adding too many of these gases to our atmosphere and thus warming the planet?

(1) http://www.ucar.edu/learn/1_3_1.htm

(2) http://www.msc.ec.gc.ca/saib/climate/FAQ_2002/sections/2_e.html