Glitter Words

Greenhouse Effect

The greenhouse effect is the process in which the emission of infrared radiation by the atmosphere warms a planet's surface. The name comes from an incorrect analogy with the warming of air inside a greenhouse compared to the air outside the greenhouse. The greenhouse effect was discovered by Joseph Fourier in 1824 and first investigated quantitatively by Svante Arrhenius in 1896.[1]

The Earth's average surface temperature of 15 °C (59 °F) is about 33 °C (59 °F) warmer than it would be without the greenhouse effect.[2] Global warming, a recent warming of the Earth's lower atmosphere, is believed to be the result of an enhanced greenhouse effect due to increased concentrations of greenhouse gases in the atmosphere. In addition to the Earth, Mars and Venus have greenhouse effects.

Greenhouse gases

Main article: Greenhouse gas Quantum mechanics provides the basis for computing the interactions between molecules and radiation. Most of this interaction occurs when the frequency of the radiation closely matches that of the spectral lines of the molecule, determined by the quantization of the modes of vibration and rotation of the molecule. (The electronic excitations are generally not relevant for infrared radiation, as they require energy larger than that in an infrared photon.)

The width of a spectral line is an important element in understanding its importance for the absorption of radiation. In the Earth’s atmosphere these spectral widths are primarily determined by “pressure broadening”, which is the distortion of the spectrum due to the collision with another molecule. Most of the infrared absorption in the atmosphere can be thought of as occurring while two molecules are colliding. The absorption due to a photon interacting with a lone molecule is relatively small. This three-body aspect of the problem, one photon and two molecules, makes direct quantum mechanical computation for molecules of interest more challenging. Careful laboratory spectroscopic measurements, rather than ab initio quantum mechanical computations, provide the basis for most of the radiative transfer calculations used in studies of the atmosphere.

The molecules/atoms that constitute the bulk of the atmosphere: oxygen (O2), nitrogen (N2) and argon (Ar); do not interact with infrared radiation significantly. While the oxygen and nitrogen molecules can vibrate, because of their symmetry these vibrations do not create any transient charge separation. Without such a transient dipole moment, they can neither absorb nor emit infrared radiation. In the Earth’s atmosphere, the dominant infrared absorbing gases are water vapor, carbon dioxide, and ozone (O3). The same molecules are also the dominant infrared emitting molecules. CO2 and O3 have "floppy" vibration motions whose quantum states can be excited by collisions at energies encountered in the atmosphere. For example, carbon dioxide is a linear molecule, but it has an important vibrational mode in which the molecule bends with the carbon in the middle moving one way and the oxygens on the ends moving the other way, creating some charge separation, a dipole moment, thus carbon dioxide molecules can absorb IR radiation. Collisions will immediately transfer this energy to heating the surrounding gas. On the other hand, other CO2 molecules will be vibrationally excited by collisions. Roughly 5% of CO2 molecules are vibrationally excited at room temperature and it is this 5% that radiates. A substantial part of the greenhouse effect due to carbon dioxide exists because this vibration is easily excited by infrared radiation. CO2 has two other vibrational modes. The symmetric stretch does not radiate, and the asymmetric stretch is at too high a frequency to be effectively excited by atmospheric temperature collisions, although it does contribute to absorption of IR radiation. The vibrational modes of water are at too high energies to effectively radiate, but do absorb higher frequency IR radiation. Water vapor has a bent shape. It has a permanent dipole moment (the O atom end is electron rich, and the H atoms electron poor) which means that IR light can be emitted and absorbed during rotational transitions, and these transitions can also be produced by collisional energy transfer. Clouds are also very important infrared absorbers. Therefore, water has multiple effects on infrared radiation, through its vapor phase and through its condensed phases. Other absorbers of significance include methane, nitrous oxide and the chlorofluorocarbons.

Discussion of the relative importance of different infrared absorbers is confused by the overlap between the spectral lines due to different gases, widened by pressure broadening. As a result, the absorption due to one gas cannot be thought of as independent of the presence of other gases. One convenient approach is to remove the chosen constituent, leaving all other absorbers, and the temperatures, untouched, and monitoring the infrared radiation escaping to space. The reduction in infrared absorption is then a measure of the importance of that constituent. More precisely, define the greenhouse effect (GE) to be the difference between the infrared radiation that the surface would radiate to space if there were no atmosphere and the actual infrared radiation escaping to space. Then compute the percentage reduction in GE when a constituent is removed. The table below is computed by this method, using a particular 1-dimensional model of the atmosphere. More recent 3D computations lead to similar results.

Gas removed percent reduction in GE H2O 36% CO2 9% O3 3% (Source: GISS-GCM ModelE simulation) [4]

By this particular measure, water vapor can be thought of as providing 36% of the greenhouse effect, and carbon dioxide 9%, but the effect of removal of both of these constituents will be greater than the total that each reduces the effect, in this case more than 45%. An additional proviso is that these numbers are computed holding the cloud distribution fixed. But removing water vapor from the atmosphere while holding clouds fixed is not likely to be physically relevant. In addition, the effects of a given gas are typically nonlinear in the amount of that gas, since the absorption by the gas at one level in the atmosphere can remove photons that would otherwise interact with the gas at another altitude. The kinds of estimates presented in the table, while often encountered in the controversies surrounding global warming, must be treated with caution. Different estimates found in different sources typically result from different definitions and do not reflect uncertainties in the underlying radiative transfer.

Global warming

Global warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-twentieth century and its projected continuation.

The global average air temperature near the Earth's surface rose 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the hundred years ending in 2005.[1] The Intergovernmental Panel on Climate Change (IPCC) concludes "most of the observed increase in globally averaged temperatures since the mid-twentieth century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations"[1] via the greenhouse effect. Natural phenomena such as solar variation combined with volcanoes probably had a small warming effect from pre-industrial times to 1950 and a small cooling effect from 1950 onward.[2][3] These basic conclusions have been endorsed by at least thirty scientific societies and academies of science,[4] including all of the national academies of science of the major industrialized countries.[5][6][7] While individual scientists have voiced disagreement with some findings of the IPCC,[8] the overwhelming majority of scientists working on climate change agree with the IPCC's main conclusions.[9][10]

Climate model projections summarized by the IPCC indicate that average global surface temperature will likely rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the twenty-first century.[1] The range of values results from the use of differing scenarios of future greenhouse gas emissions as well as models with differing climate sensitivity. Although most studies focus on the period up to 2100, warming and sea level rise are expected to continue for more than a thousand years even if greenhouse gas levels are stabilized. The delay in reaching equilibrium is a result of the large heat capacity of the oceans.[1]

Increasing global temperature will cause sea level to rise, and is expected to increase the intensity of extreme weather events and to change the amount and pattern of precipitation. Other effects of global warming include changes in agricultural yields, trade routes, glacier retreat, species extinctions and increases in the ranges of disease vectors.

Remaining scientific uncertainties include the amount of warming expected in the future, and how warming and related changes will vary from region to region around the globe. Most national governments have signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions, but there is ongoing political and public debate worldwide regarding what, if any, action should be taken to reduce or reverse future warming or to adapt to its expected consequences.

The 10 Biggest Energy Users
1. Water heaters
2. Refrigerators
3. Freezers
4. Air conditioners
5. Ranges
6. Clothes washers
7. Clothes dryers
8. Dishwashers
9. Portable heaters
10. Lights


Pollution can take many forms. The air we breathe, the water we drink, the ground where we grow our food, and even the increasing noise we hear every day—all contribute to health problems and a lower quality of life. Find out about the environment issues of pollution, what’s being done on a global level, and what you can do in your community.

Ozone Depletion

What is ozone depletion? And how does ozone depletion affect the earth? Learn about the causes and effects of ozone depletion, and how it changes the environment for humans, animals, and plants.

Ozone is a gas that occurs both in the Earth's upper atmosphere and at ground level. Ozone can be "good" or "bad" for people's health and for the environment, depending on its location in the atmosphere. For an overview of both ozone issues, see Good Up High, Bad Nearby.

Ground-level Ozone
In the troposphere, the air closest to the Earth's surface, ground-level or "bad" ozone is a pollutant that is a significant health risk, especially for children with asthma. It also damages crops, trees and other vegetation. It is a main ingredient of urban smog.

Observe speed limits. The typical car uses 17% more gas when driven at 65 miles per hour than at 55 mph. At 70 mph, you use about 25% more gas.

 Avoid jump starts. Never put the “pedal to the metal” unless your life is in danger. Doing so can burn as much as 50% more gas than a relatively smooth start.

 Accelerate smoothly and moderately. When you reach your desired speed, use just enough gas to maintain your speed. Pretend there’s a full glass of water on the seat next to you.

 Don’t ride your brake. You’d be surprised how many people drive with one foot on the accelerator and the other on the brake. This is unsafe, wastes gas, and prematurely wears down brake shoes.

 Avoid peak-period travel. Travel outside of “rush-hour.” You’ll save gas — and time. When average speeds drop from 30 mpg to 10 mpg, fuel use doubles. 

4-steps to Set Up a Successful Waste Separation and Recovery Program

Step 1 - Understand the Waste Recovery System in H.K.

Nearly 1.54 million tonnes of recyclables were recovered from the municipal waste stream in 1997. Waste recovery has been achieved mainly in the following ways :
waste generators (mainly industrial) separate recyclables from their waste and sell the recovered materials directly to scrap traders/recyclers;
"scavengers" and cleansing staff separate valuable materials from the mixed waste stream and sell the recovered materials to scrap traders for further processing;
organisations such as schools, housing estates, government departments, community bodies, etc. organise, for environmental protection purpose, their own waste recovery schemes and sell/give the recovered materials to scavengers or scrap traders.

Step 2 - Identify Your Valuable Waste Components

As waste recovery in Hong Kong is market driven, the availability of market for any waste to be recovered in your programme would be an important factor affecting the successfulness of your programme. It is advisable for you to have a look at the waste stream first and identify the valuable waste components. You can make use of Appendix I to prepare a list of potentially marketable recyclables and record the estimated quantities. The common recyclables in our refuse include paper, plastic, ferrous metal, non-ferrous metal and glass bottle.

Step 3 - Acquire an Outlet for Your Recyclables

To confirm if there would be an outlet for the recyclables to be recovered in your programme and to finalise the list of recyclables to be recovered, you can contact the following potential "buyer" of your recyclables :

1.Scrap Trade and Recyclers (suitable for large scale programme)

List of scrap traders (recyclable collectors) and recyclers are available from EPD through the telephone hotline of 2838 3111. Collection service might be provided by these collectors depending on the quantity of recyclables and location. A procedural checklist is attached in Appendix II for you to record the requirements of and services provided by different collectors.

2.Cleansing Agent (suitable for smaller scale programme)

The profit obtained by selling the recyclables to scrap traders/recyclers sometimes creates an incentive for the cleansing staff to collect even a small quantity of recyclables. You can thus liaise with your janitor to see if he/she is interested in the recovering the recyclables. For larger scale programmes covering a whole building or estate, it is possible to involve the cleansing contractor of that building or estate.

Step 4 - Draw up Your Implementation Programme

After securing a recyclable outlet for your programme and finalising the list of recyclables to be recovered, you need to draw up an implementation programme for your waste recovery initiative. Sufficient and continuous commitment from both the organiser and the participants, clear instructions on waste separation procedures, continuous monitoring and review on the achievements of the programme are among the essential elements for a successful waste recovery programme. More detailed illustration of the essential elements of such an implementation programme can be found in "Appendix III. Please contact EPD's Hotline Service at 2838 3111 for enquiry or if you need further help.

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