Global Warming - Part 2 - The Greenhouse Effect
Updated: Aug 30
The Greenhouse Effect – The greenhouse effect is caused by the interaction between our atmosphere and the sun’s rays. It is essential to life, since it keeps us from all becoming ice cubes. If you’ve been in a greenhouse, you know know the feeling of trapped heat. Here’s a link to an animated diagram that explains the greenhouse effect in detail.
Here’s the basic mechanism from Wikipedia, which shows that it is not as simple as what happens in an enclosed glass structure:
The Earth receives energy from the Sun mostly in the form of visible light and nearby wavelengths. About 50% of the sun’s energy is absorbed at the Earth’s surface, the rest is reflected or absorbed by the atmosphere. The absorbed energy warms the surface. Simple presentations of the greenhouse effect, such as the Idealized greenhouse model, show this heat being lost as thermal radiation. The reality is somewhat more complex: the atmosphere near the surface is largely opaque to thermal radiation (with important exceptions for “window” bands), and most heat loss from the surface is by sensible heat and latent heat transport. However, radiative effects become increasingly important higher in the atmosphere as the higher levels become progressively more transparent to thermal radiation, largely because the atmosphere is drier and water vapor – an important greenhouse gas – becomes less. It is more realistic to think of the greenhouse effect as applying to a “surface” in the mid-troposphere, which is effectively coupled to the surface by a lapse rate.
Within the region where radiative effects are important, the presentation of the Idealized greenhouse model becomes more reasonable: a layer of atmosphere with greenhouses gases will radiate heat in all directions, both upwards and downwards, thereby warming the surface and simultaneously cooling the atmosphere by transmitting heat to deep space at 2.7K. Increasing the concentration of the gases increases the amount of radiation, and thereby warms the surface more.
The greenhouse effect is essential for life, however, the rising levels of greenhouse gases have caused increasing amounts of heat from the sun to become trapped at ground level. Much of this trapped heat is accumulated in the world’s oceans. According to the National Oceanic and Atmospheric Administration, in the last 50 years, 22 times as much heat has been absorbed by the oceans as has been absorbed by the atmosphere. The heating up of the oceans drives changes in weather, like heavier precipitation events, sequences of large storms, cold spells and increasing drought conditions in some areas.
Our leading universities are advancing the science of global warming. The Center for Health and the Global Environment at the Harvard Medical School is one good resource for detailed research on the subject.
Please keep coming back to my blog, as we continue our study of global warming. Please post comments so we can start a discussion on this contentious issue.