Global Warming

 

Definition
Global warming = Change of climate

Climate change is any substantial change in Earth’s climate that lasts for an extended period of time.  Global warming refers to climate change that causes an increase in the average temperature of the lower atmosphere.  Global warming can have many different causes, but it is most commonly associated with human interference, specifically the release of excessive amounts of greenhouse gases.

Greenhouse gases, such as carbon dioxide (CO2), methane (CH4), water vapor, and fluorinated gases, act like a greenhouse around the earth.  This means that they let the heat from the Sun into the atmosphere, but do not allow the heat to escape back into space.  The more greenhouse gases there are, the larger the percentage of heat that is trapped inside the earth’s atmosphere.  The earth could not exist in its present state (that is, with life) without the presence of some naturally occurring greenhouse gases, such as CO2, CH4, and water vapor. Without any greenhouse gases no heat would be trapped in atmosphere, so the earth would be extremely cold. (NASA, 2002)

Naturally occurring greenhouse gases (not fluorinated gases) are good in naturally occurring amounts; it’s when people start contributing excessive amounts of them that greenhouse gases become a problem.  With excessive greenhouse gas buildup, the earth’s atmosphere warms to unnatural temperatures which causes, among other things, sea level to rise.  Global warming also causes sea surface temperatures to rise, precipitation patterns to change, etc.

Aren’t temperature changes natural?

The average global temperature and concentrations of carbon dioxide (one of the major greenhouse gases) have fluctuated on a cycle of hundreds of thousands of years as the Earth’s position relative to the sun has varied. As a result, ice ages have come and gone.

However, for thousands of years now, emissions of GHGs to the atmosphere have been balanced out by GHGs that are naturally absorbed.  As a result, GHG concentrations and temperature have been fairly stable. This stability has allowed human civilization to develop within a consistent climate.

Occasionally, other factors briefly influence global temperatures.  Volcanic eruptions, for example, emit particles that temporarily cool the Earth’s surface.  But these have no lasting effect beyond a few years. Other cycles, such as El Niño, also work on fairly short and predictable cycles.

Now, humans have increased the amount of carbon dioxide in the atmosphere by more than a third since the industrial revolution. Changes this large have historically taken thousands of years, but are now happening over the course of decades.