What is the greenhouse effect and how is radiation involved?

Answer 1

Thermal radiation is the electromagnetic radiation given off by an object. If you heat up a piece of steel enough it starts to glow and you can see some of the radiation as visible light. At normal room temperature it is still "glowing" but the glow is in the infra-red spectrum that we can't see with our eyes. Everything around us glows like this. The hotter it is the more energy it emits.

The greenhouse effect is best described by starting with a greenhouse, you know, the little glass shed at the bottom of the garden where you grow plants. I know this isn't what you want to know about but bear with me……

In our greenhouse the sun shines in through the glass bringing in lots of energy as light. The light energy is a mixture of all the visible colours. (Plus some ultra-violet which we can't see.) If you think about it you know glass lets visible light through, if you don't know look out the window, since you can see what is outside you have just proved that glass lets visible light through. :-)

This light energy from the sun coming through the glass is absorbed by the plants, the benches the plants are sitting on, the floor, etc. making them warmer. Because they are warmer they emit more infrared energy, if the glass wasn't there this infra-red light would radiate away and things would not get very much warmer but glass happens not to let infra-red light through, it is transparent to visible light but not to infra-red light so the infra-red can't escape from the greenhouse, some is reflected back by the glass to be reabsorbed inside the greenhouse, the rest is absorbed by the glass making the glass hotter which in turn emits more infra-red light into the greenhouse. Result - The greenhouse traps solar energy and gets warmer.

Now to what we normally mean by the greenhouse effect these days, the warming of the planet due to gasses in the atmosphere. The Earth has always had a greenhouse effect; the Earth's atmosphere is more transparent to visible light than to infrared so just like in our actual greenhouse example above, when the Sun shines on the Earth the incoming high energy visible light passes through the atmosphere to warm the surface of the planet. Because the surface is warmed it emits more infrared light some of which is absorbed or reflected by the atmosphere meaning the Earth gets warmer than it would be without the greenhouse effect. This is just as well, without any greenhouse effect the average temperature would be about 32°C cooler! It is pretty essential to life on Earth.

The problem is that mankind has been emitting a number of gasses that make the Earth's atmosphere less transparent to infrared light, particularly carbon dioxide but also methane, nitrous oxide and the chlorofluorocarbons. These increase the greenhouse effect.

Thus far everything is scientific fact and pretty much beyond dispute. Now we get to the bit where there has been debate. It is now generally thought that the volumes of greenhouse gases being emitted by mankind are at a level significantly beyond the ability of the Earth's natural mechanisms to deal with and they are already having an effect on the temperature of the Earth. If we continue to emit these gases at current levels then there are going to be significant warming of the climate of the Earth.

There is now a general consensus amongst scientists that atmospheric emissions by mankind will result in an increase in the temperature but there is still a significant range in the projections for temperature change. There are still scientists who do not believe that the effect will be significant but they are now in a very small minority.

Note - The greenhouse effect ironically isn't actually the main reason an actual greenhouse gets warm. The main reason is the prevention of convection but the explanation given above is the one that was believed to be true when the effect was named and is useful when we come to talk about the Earth.

Answer 2

The greenhouse effect we should be concerned about is the enhanced greenhouse effect caused by the additional greenhouse gases in the atmosphere. They are additional because they come from the burning of fossil fuels (coal, oil and natural gas). Fossil fuels have kept their carbon safely underground for 300 million years. Now we have dug it up and are releasing it all into the atmosphere.

We need to be concerned because the enhanced greenhouse effect will cause global warming which in turn melts glaciers and other ice caps which can flood most of the world. It can also cause many organisms to die, including humans.

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Note that the major greenhouse gas in our atmosphere is WATER (95% of greenhouse gases are water vapour) - although the main greenhouse gases that referred to in the media are such things as carbon dioxide and methane. The greenhouse effect is actually very important to us - because the water vapor in the atmosphere helps hold in so much solar energy, the earth remains far more temperate than it would otherwise be. Without the greenhouse effect, during the day earth would heat up, but at night, all the accumulated energy would radiate back into space and the planet's surface temperature would fall far below zero very rapidly. The reason this doesn't happen is that earth's atmosphere contains molecules that absorb the heat and re-radiate the heat in all directions. This reduces the heat radiated out to space. Called 'greenhouse gases' because they serve to hold heat in like the glass walls of a greenhouse, these molecules are responsible for the fact that the earth enjoys temperatures suitable for our active and complex biosphere. Note that we actually see some of this phenomena in desert areas where it can be blistering hot during the day and cold at night because there is so little water vapor in the desert air to hold in the heat at night.

The current concern is that the concentrations of some of the lesser greenhouse gases are increasing which is believed to be a significant factor in the upward shift of the average temperature of of the earth of roughly 0.5 °C since the 1970s. That seems minor but if the average temperature dropped by 5 °C we would be looking at a new ice age while an increase of that much would melt much of the arctic and antarctic ice changing ocean levels significantly and drastically altering which latitudes are temperate (we grow most of our crops in the temperate zones). While water is the primary greenhouse gas, fairly small changes in temperature change the amount of water in the atmosphere - both as water vapor and clouds. Humid air causes temperature rises; more clouds cause cooling (by reflecting solar energy back out before it reaches the earth). The concern is that small temperature changes due to increases in the other (i.e. besides water vapor) greenhouse gases will become magnified as more water enters the atmosphere.

Unfortunately all the climate models we have are still much more simple than the extremely complex reality of our planet and it's climate. Many factors are only roughly accounted for in current models - CO2 uptake by plants, deforestation decreasing available plants to absorb the CO2, changes in the distribution of plants, ocean currents, CO2 absorption and release by the ocean. Increases, decreases, and shifts in types of ocean organisms that absorb and release greenhouse gases, exchange of surface ocean water with deep ocean water, solar cycles ... hopefully you get the point, i.e. that there are a LOT of variables that must be accounted for and some of them interact in ways we still don't fully understand. At best, we have a rough idea of what to expect. Current models do a decent job at predicting trends over long periods of time but still manage to fail a lot of the time when it comes to short term predictions.

The main concerns right now are that anthropogenic (coming from human activities) greenhouse gas increases will result in significant changes in local climates - rendering some area that are currently fertile less fertile or even barren, melting ice caps resulting in significant changes in ocean levels which would in turn significantly affect those living in coastal areas (note that coastal areas are more heavily populated than inland areas in most of the world). There are also concerns that different sides in the political debates are cherry-picking their results to support political and economic policies unrelated to potential climate change. As an example: those advocating a re-distribution of wealth from more prosperous nations to poorer ones sometimes use worries about global warming to advocate placing heavy burdens on developed nations to reduce their carbon emissions while not asking nations like India and China to do the same; such uneven distribution of responsibility is based primarily on politics rather than science. Also changes in climate may reduce water availability in some regions where it is already a source of conflict - such as between Turkey and its neighbors. This could significantly increase political tensions in those affected areas and potentially lead to wars.

So yeah - global warming is a cause for concern for a LOT of reasons.

Answer 3

well greenhouse effect is the rise in temperature that the earth experiences

that is true

trust me

Its not true. for real. Trust me.

Answer 4

true