| Lecture 0 Notes September 29, 2004 |
Global Warming: Temperature increase at the surface and atmosphere
due to an anthropogenic enhancement of the greenhouse effect.
Greenhouse Effect: The process of gases in the atmosphere emitting
infrared radiation and thereby warming a planet's surface above the level
of an atmosphere-free planet. The gases are themselves warmed by absorbing
solar radiation and infrared radiation.
Climate Change: Long-term fluctuations in the climate, not
necessarily of anthropogenic origin.
This schematic of the Greenhouse Effect was created by Prof. Dennis Hartmann (chair of Atmospheric Sciences Department). It resembles Fig 3.19 in your textbook. The term "Longwave Radiation" is synonamous with "Infrared Radiation" and "Radiant Heat". The type of radiation, which is defined by its wavelength, depends on the temperature of the emitting object. We will discuss these concepts in greater detail when we study Chapter 3. For now, please recognize that the Greenhouse Effect is a well understood and non-controversial phenomena.
Someone in class asked why the "Back Radiation" branch was so much higher than the "Outgoing longwave Radiation". I answered that the temperature profile of the atmosphere decreases with height. I should have also mentioned that these arrows represent the emitted radiation from the whole atmosphere on average. A single molecule emits the same radiation up and down
(in all directions actually).
Someone else asked if clouds didn't also have a blanketing effect. First try not to compare the greenhouse effect with a blanket. A blanket prevents warm air from escaping. The atmosphere is very fluid and doesn't simply obstruct heat from circulating. About clouds though - yes they emit infrared radiation like a gas and like the planet's surface. And yes you could call it a greenhouse effect because the process is essentially the same. One important difference between clouds and greenhouse gases is that removing clouds doesn't necessarily make the planet colder because they block sunlight.
I also discussed the difference between climate and weather, which is a bit nebulous really. A record of temperature recorded every hour for many months or years clearly has a fuzz of fluctuations that often span 5-10C or more on top of a seasonal cycle. The seasonal cycle doesn't repeat itself exactly from year-to-year. In this case, the fuzz is "weather" and the seasonal and year-to-year fluctuations are "climate". But don't be surprised if climatologists are a bit sloppy with these terms. Climate science is an evolving field. I'll try to distinguish fundamental facts, like the greenhouse effect, from less firm ideas and terminology in this course.
Contact the instructor at: atms211@atmos.washington.edu
Last Updated: 9/29/2004