Carbon Dioxide: A Greenhouse Gas

Carbon dioxide is a greenhouse gas.

This means it traps heat from the sun in the atmosphere. Most of the time this is beneficial to us, because without greenhouse gases to trap heat, the planet would be a lot colder.

95% of CO2 emissions are from natural sources

natural decay of organic material releases 8x more carbon dioxide than human beings

Carbon dioxide is released to the atmosphere by a variety of natural sources, and over 95% of total CO2 emissions would occur even if humans were not present on Earth.
For example, the natural decay of organic material in forests and grasslands, such as dead trees, results in the release of about 220 gigatonnes of carbon dioxide every year. This carbon dioxide alone is over 8 times the amount emitted by humans.

Natural sources of atmospheric carbon dioxide further include volcanic outgassing and the respiration processes of living organisms. (When we breathe we exhale carbon dioxide, and so do most other living beings except plants which absorb carbon dioxide and release oxygen.)

So why are we so worried about the tiny percentage of CO2 emitted by humans?

Although natural sources represent most CO2 emissions, they do not contribute to the recent observed increase in concentrations because natural sources are balanced by natural sinks that remove carbon dioxide from the atmosphere.
The increase in carbon dioxide concentration arises because the increase from human activity is not completely balanced by a corresponding sink.

Why is an increase in carbon dioxide worrisome?

Temperature and atmospheric carbon dioxide correlation

Carbon dioxide levels are now higher than at any point in human history.

The oldest human fossil found (named Lucy and found in Ethiopia) has been dated back to between 3 and 3.6 million years ago. However, Lucy was not a Homo Sapiens.
The earliest Homo Sapien found to date is 200,000 years old.
It’s still possible a Homo Sapien could be found that dates back 400,000 years or longer, but at the moment that’s all we know: Humans as we know them, have walked the Earth for no more than 200,000 years.
Considering that Dinosaurs were on the Earth for 250 million years, it’s truely remarkable what humans have achieved in only 200,000 years!
Unfortunately not all human achievements are good.

Today carbon dioxide levels are more than three hundred eighty parts per million, far above carbon dioxide levels ever registered since human beings evolved.
This enormous rise has taken place in a very short time. Shorter ice cores from Antarctica and Greenland have shown that between 1000 AD and the mid-1800s Carbon Dioxide levels remained fairly constant at about two hundred ninety parts per million.
Since then, in pace with the industrial revolution, CO2 levels have climbed to levels not reached at any time in the past half million years.

CO2 levels have risen thirty percent over the last hundred and fifty years alone.
Scientists link this finding to a simultaneous increase in CO2 emissions caused by human activities. Therefore present day scientists agree that Global Warming is, with virtual certainty, due to human actions.

How will today’s CO2 emissions influence our future?

Therefore carbon dioxide will continue to trap heat in the atmosphere long after we stop emitting any greenhouse gas. The consequences of what we do now, will be felt for centuries to come. That’s why it’s so important that we stop emitting carbon dioxide as soon as we can.

The cooling effect of Aerosols.

Cars and power plants which are the primary sources of carbon dioxide emissions also produce aerosols such as smoke and fumes, which actually have a cooling effect on global temperatures. Some scientists think that the magnitude of this cooling approximately cancels out the warming effect of carbon dioxide.

Cool, you may think. We can just keep on driving our cars, without a worry about global warming.

Unfortunately the problem is a bit more complex.
 

Aerosols are short lived.

Another thing to keep in mind is that some aerosols even have the opposite effect and contribute to Global Warming.

Black Carbon Aerosols.

It turns out that black carbon, an aerosol emitted by diesel engines, the open burning of forests, and the residential burning of coal, wood, dung, and agricultural residues actually has a warming effect.
Scientists recently discovered that black carbon aerosols likely account for forty-five percent or more of the warming which has occurred in the Arctic during the last three decades.

Sources:
http://co2.cms.udel.edu/Increasing_Atmospheric_CO2.htm
http://en.wikipedia.org/wiki/Atmospheric_CO2