Greenhouse effect

Greenhouse effect
From Wikipedia, the free encyclopedia

A representation of the exchanges of energy between the source (the Sun), the Earth's surface, the Earth's atmosphere, and the ultimate sink outer space. The ability of the atmosphere to capture and recycle energy emitted by the Earth surface is the defining characteristic of the greenhouse effect.

Another diagram of the greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases.
Solar radiation at the frequencies of visible light largely passes through the atmosphere to warm the planetary surface, which then emits this energy at the lower frequencies of infrared thermal radiation. Infrared radiation is absorbed by greenhouse gases, which in turn re-radiate much of the energy to the surface and lower atmosphere. The mechanism is named after the effect of solar radiation passing through glass and warming a greenhouse, but the way it retains heat is fundamentally different as a greenhouse works by reducing airflow, isolating the warm air inside the structure so that heat is not lost by convection.
If an ideal thermally conductive blackbody were the same distance from the Sun as the Earth is, it would have a temperature of about 5.3 °C. However, since the Earth reflects about 30% of the incoming sunlight, this idealized planet's effective temperature (the temperature of a blackbody that would emit the same amount of radiation) would be about −18 °C. The surface temperature of this hypothetical planet is 33 °C below Earth's actual surface temperature of approximately 14 °C. The mechanism that produces this difference between the actual surface temperature and the effective temperature is due to the atmosphere and is known as the greenhouse effect.
Earth’s natural greenhouse effect makes life as we know it possible. However, human activities, primarily the burning of fossil fuels and clearing of forests, have intensified the natural greenhouse effect, causing global warming.

From Wikipedia, the free encyclopedia
For other uses, see Greenhouse (disambiguation).

A greenhouse (also called a glasshouse) is a building or complex in which plants are grown. These structures range in size from small sheds to industrial-sized buildings. A miniature greenhouse is known as a cold frame.
Commercial glass greenhouses are often high tech production facilities for vegetables or flowers. The glass greenhouses are filled with equipment like screening installations, heating, cooling, lighting and also may be automatically controlled by a computer to maximize potential growth.
A greenhouse is a structural building with different types of covering materials, such as a glass or plastic roof and frequently glass or plastic walls; it heats up because incoming visible sunshine is absorbed inside the structure. Air warmed by the heat from warmed interior surfaces is retained in the building by the roof and wall; the air that is warmed near the ground is prevented from rising indefinitely and flowing away. This is not the same mechanism as the "greenhouse effect".

What is a Greenhouse?
Copyright InformationModified with permission from Global ClimatesPast, Present, and Future, S. Henderson, S. Holman, and L. Mortensen (Eds.), EPA Report No. EPA/600/R-93/126. U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC, 39 - 44.
This activity is designed to have students become familiar with how a greenhouse retains heat by building simple models. Through discussion, you can explain how the atmospheric 'greenhouse effect' retains heat.

Greenhouses are used extensively by botanists, commercial plant growers, and dedicated gardeners. Particularly in cool climates, greenhouses are useful for growing and propagating plants because they both allow sunlight to enter and prevent heat from escaping. The transparent covering of the greenhouse allows visible light to enter unhindered, where it warms the interior as it is absorbed by the material within. The transparent covering also prevents the heat from leaving by reflecting the energy back into the interior and preventing outside winds from carrying it away.
Like the greenhouse covering, our atmosphere also serves to retain heat at the surface of the earth. Much of the sun's energy reaches earth as visible light. Of the visible light that enters the atmosphere, about 30% is reflected back out into space by clouds, snow and ice-covered land, sea surfaces, and atmospheric dust. The rest is absorbed by the liquids, solids, and gases that constitute our planet. The energy absorbed is eventually reemitted, but not as visible light (only very hot objects such as the sun can emit visible light). Instead, it's emitted as longer-wavelength light called infrared radiation. This is also called "heat" radiation, because although we cannot see in infrared, we can feel its presence as heat. This is what you feel when you put your hand near the surface of a hot skillet. Certain gases in our atmosphere (known as "trace" gases because they make up only a tiny fraction of the atmosphere) can absorb this outgoing infrared radiation, in effect trapping the heat energy. This trapped heat energy makes the earth warmer than it would be without these trace gases.
The ability of certain trace gases to be relatively transparent to incoming visible light from the sun yet opaque to the energy radiated from earth is one of the best-understood processes in atmospheric science. This phenomenon has been called the "greenhouse effect" because the trace gases trap heat similar to the way that a greenhouse's transparent covering traps heat. Without our atmospheric greenhouse effect, earth's surface temperature would be far below freezing. On the other hand, an increase in atmospheric trace gases could result in increased trapped heat and rising global temperatures.

Average house size by country
If you asked all the people of the world whether they would prefer a bigger or smaller house I’d guess almost everyone would plump for more space.  That makes perfect sense for people living in small and overcrowded spaces, but is there a point at which we have enough space?
To get a little perspective I’ve put together a graphic to illustrate how big the average new home is around the world.
The figures are in square-meters of usable floor space, and include data for both houses and flats.
In the countries I could get data for the average new home varied in size from 45 m2 (484 ft2) in Hong Kong up to 214 m2 (2,303 ft2) in Australia.
US home size has fallen a little since the recession, to 201 m2 (2,164 ft2) in 2009.  UK house size is relatively small at  76 m2 (818 ft2) while Canadian houses are quite big at 181 m2 (1,948 ft2).  For China the data only reflects urban properties, which now average 60 m2 (646 ft2) and have almost doubled in size in the last 15 years.
There are all sorts of reasons for these differences.  Wealth levels, urbanization rates, land access and climate all play a part.  Nonetheless the scale of the differences is pretty fascinating.
The thing that is really missing from this picture is people.
Average floor space per person
We can take our analysis a little further by looking at how much floor space this equates to per person.
Using data on average household size we can estimate floor space per inhabitant for new homes.  This analysis is a bit rough and ready, as it assumes new homes are being built for the average household.  Nonetheless it is useful because it helps to control for the considerable differences in household size between countries.
At just 15 m2 (161 ft2) a person in Hong Kong has just a quarter of the floor space of the average Australian or American.
If Graham Hill lives by himself then his trendy 39  m2 (420 ft2) is similar to someone from Sweden.  In fact in the range from 30-45  m2 (323-484 ft2) are the averages for Italy, the UK, Japan, Spain, Sweden, France and Greece.
At our place we have 110  m2(1,184 ft2) for a family of four, which is 27  m2 (291 ft2) per person.  Having previously lived in a few different flats of 50-60 m2 as a couple this feels pretty palatial, and is certainly more than enough for us.  But 30  m2 per person is much more generous in a four person family than it is in a studio apartment for one.
In London they have a new minimum space standard as part of the London Plan.  For new flats the minimum standards are 37 m2 (398 ft2) for one person, 50 m2 (538 ft2) for two people in one bedroom, 61 m2 (657 ft2) for three people with two bedrooms, 70 m2 (753 ft2) for four people in two bedrooms and 74 m2 (797 ft2) for four people in three bedrooms.  Are these enough space?
In my mind if you have decent ceiling heights, good windows, clever storage and not too much stuff a little space can go a long way.

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