EGEE 101
Energy and the Environment

Climate Change

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Climate Change vs. Global Warming

Climate Change is the preferred term to describe the rapid changing of the climate that we (the planet) are experiencing mainly since the 1900s. It is related to global warming.

Global Warming is the increase in temperature (generally) that has been occurring mainly since the 1900s. The issue, however, is not simply, that on average, the planet's temperature is warming. Rather, if you agree that the climate will get warmer, then it makes sense that the warming will affect the water cycle and that, in turn, (coupled with a warming) will influence the climate. Global warming is the often used term, but not by my students who know better — climate change, please!

What is the difference?

Not all of the areas of the planet are likely to experience a warming. Some areas will experience a cooling, so climate change is the preferred terminology. Also warming in some areas may prove beneficial but without water this benefit will be lost. Alternatively, if there is a change in the precipitation (rain, snow, hail, etc.) pattern as you would expect if the temperature changes, then too much or too little water can both be disastrous. Thus we are experiencing change, not just warming! Some plants will grow quicker and larger, while others will not grow, so change is the key term.

The Greenhouse Effect

The greenhouse effect is a highly beneficial process where the planet is warmed by greenhouse gases helping to trap some of the radiation that would have otherwise escaped back into space. Without greenhouse gases the surface temperature of the planet would be an average –18 °C (0 °F)! Chilly.

Greenhouse Gases

 Link to the Greenhouse effect infographic. See caption for details.
The greenhouse effect works because of IR radiation coming from the surface of the planet and IR absorbing molecules in the atmosphere. They absorb then emit IR in all directions, a portion going back to the earth surface. Click on the image to see an enlarged view.
Credit: United Nations Environment Programme / GRID-Arendal

Greenhouse Gases are gases (in the atmosphere) that will absorb infrared radiation (learn more about the electromagnetic spectrum). Naturally released greenhouse gases include water (H2O), carbon dioxide (CO2), methane (CH4) & nitrous oxide (N2O) (a.k.a. laughing gas). Ultra Violet radiation (UV) will penetrate the atmosphere and a portion will be absorbed by the surface of the planet. When radiated back into the atmosphere it will be in the form of Infrared radiation (IR), thus some of this IR radiation will be absorbed by greenhouse gases. Being dumb molecules they don’t know which is up or down so after “doing their thing” they get “tired” and re-emit the IR radiation, a portion of which goes back to earth warming the planet. (Click on the molecule to see the molecule "Doing its thing".) "Doing their thing" implies the excited state of the molecule. Through a series of bond stretching, bending, wagging etc. the molecule uses the energy (without significant losses). This is an example of methane going through its excited states within the IR spectrum. The IR spectrum of an unknown gas can be used to identify some gases or their relative portions.

 Link to an animation of a molecule doing its thing. See caption for details.
Click on the image to see molecule of Methane "doing its thing."

Providing the concentrations of the greenhouse gases remain the same, other than normal seasonal temperature fluctuations, the planet will have a relatively stable temperature year to year. Of course, there are natural cycles in place that both remove and replace these greenhouse gases in the atmosphere. The National Academy of Science has a nice graphic explanation of the greenhouse effect.

Climate Change vs. the Weather

 Degrees Fahrenheit in Pittsburgh, PA over a year.
Daily mean maximum temperature and extremes for Pittsburgh, Pennsylvania

It is tempting on a very hot day to say: “that bloody global warming again!” But that would be incorrect. We do not say: “bloody ice age” on those very cold days (although predictions were made when I was a lad that we were about to enter a new ice age!). The weather is an event that is going to change and the temperature variations can be dramatic. Climate change occurs over a much longer time frame: at least decades! When we see a change in the average temperatures over the last 20 to 30 years then that is climate change. Climate change might influence the weather, stronger storms, more or less rain, but single weather events cannot be attributed to climate change although there is progress in linking climate change to storm strengths, etc..