Guest post by Steve Goddard

There is a considerable amount of misinformation propagated about the greenhouse effect by people from both sides of the debate. The basic concepts are straightforward, as explained here. The greenhouse effect is real. If there were no greenhouse gases in the atmosphere, earth would be a cold place. Compare Mars versus Venus – Mars has minimal greenhouse gas molecules in its’ atmosphere due to low atmospheric pressure, and is cold. By contrast, Venus has a lot of greenhouse gas molecules in its’ atmosphere, and is very hot. Temperature increases as greenhouse gas concentration increases. These are undisputed facts.

Heat is not “trapped” by greenhouse gases. The earth’s heat balance is maintained, as required by the laws of thermodynamics.

outgoing radiation = incoming radiation – changes in oceanic heat content The image below from AER Research explains the radiative balance. http://www.aer.com/scienceResearch/rc/rc.html About 30% of the incoming shortwave radiation (SW) is reflected by clouds and from the earth’s surface. 20% is absorbed by clouds and re-emitted back into space as longwave (LW) radiation. The other 50% reaches the earth’s surface and warms us. All of that 50% eventually makes it back out into space as LW radiation, through intermediate processes of convection, conduction or radiation. As greenhouse gas concentration increases, the total number of collisions with GHG molecules increases. This makes it more difficult for LW radiation to escape. In order to maintain equilibrium, the temperature has to increase. Higher temperatures mean higher energies, which in turn increase the frequency of emission events. Thus the incoming/outgoing balance is maintained.

It has been known for a long time that even a short column of air contains enough CO2 to saturate LW absorption. This has been misinterpreted by some skeptics to mean that adding more CO2 will not increase the temperature. That is simply not true, as higher GHG densities force the temperature up. There is no dispute about this in the scientific community. See the graph below:

Click for larger image

As Dr. Hansen has correctly argued, increases in atmospheric temperature cause the ocean to warm up. Thus changes the oceanic heat content become the short term imbalance in the incoming/outgoing equilibrium equation, which is not shown in the AER diagram.

The image below shows GHG absorption by altitude and wavenumber. As you can see, there is a strong absorption band of CO2 at 600/cm. That is what makes CO2 an important greenhouse gas. http://www.aer.com/scienceResearch/rc/m-proj/lbl_clrt_mls.html

The important greenhouse gases are: H2O, CO2, O3, N2O, CO and CH4. The reason why the desert can get very cold at night is because of a lack of water vapor. The same is true for Antarctica. The extreme cold in Antarctica is due to high albedo and a lack of water vapor and clouds in the atmosphere, which results in almost all of the incoming radiation returning immediately to space. An earth with no CO2 would be very cold. The first few tens of PPM produce a strong warming effect, and increases after that are incremental. It is widely agreed that a doubling of CO2 will increase atmospheric temperatures by about 1.2C, before feedbacks. So the debate is not about the greenhouse effect, it is about the feedbacks. Suppose that the amount of reflected SW from clouds increases from 20% to 21%? That would cause a significant cooling effect. Thus the ability of GCM models to model future temperatures is largely dependent on the ability to model future clouds. Cloud modeling is acknowledged to be currently one of the weakest links in the GCMs. Given the sensitivity to clouds, it is perhaps surprising that some high profile climate scientists are willing to claim that 6C+ temperature rises are established science. So the bottom line is that the greenhouse effect is real. Increasing CO2 will increase temperatures. If you want to make a knowledgeable argument, learn about the feedbacks. That is where the disagreement lies. “ Lisa, in this house we obey the laws of thermodynamics “ – Homer Simpson Addenddum: The GHG/stoplight analogy Suppose that you have to drop your child at school at 8:00 and have to be at work at 8:30. There are 10 stoplights between the school and the office. Your electric car has a fixed maximum speed of 30MPH. It takes exactly 30 minutes to drive there. If the city adds another stoplight (analogous to more CO2) the only way you can make it to work on time is to run traffic lights and/or get the city to make the traffic lights more efficient at moving cars (analogous to higher temperature.) The radiative balance has to be maintained in the atmosphere, so the outgoing radiation has a fixed amount of time to escape, regardless of how many GHG molecules it encounters. Otherwise, Homer and your boss will be very angry at you for violating the laws of thermodynamics.

Share this: Print

Email

Twitter

Facebook

Pinterest

LinkedIn

Reddit



Like this: Like Loading...