There are a few words in the talk of Global Warming which make me ponder... Hmm, What exactly does greenhouse gases mean? And then before I can find that out, I get busy in something else. So, today, I'm trying to find out about those words. If you have any word that you wanna know, send it in... probably even I might not know.
Greenhouse Gases:
These gases trap the heat from the Sun and warm the Earth. They include Carbon Dioxide, Methane, Water Vapour(?), Nitrous Oxide, Ozone and Halocarbons (HydroFluoroCarbons, PerFluoroCarbons and ChloroFluoroCarbons ).
Water Vapor? Yeah, even I was surprised to know. But water vapor is a very good absorber of the long wave (/thermal) radiation, thus trapping a lot of heat and it is most prevalent in the atmosphere. Surprisingly, this natural greenhouse gas accounts to 36-70% of the greenhouse effect. (The contribution changes not by the vapor alone, but by the combination of different gases. Hence such a wide range.) But condensed water vapor forms clouds and reflect short-wave radiations from the sun. For these reasons, (loosely explained here) vapor is considered as a feedback agent than a forcing agent.
Carbon Dioxide: This is a very powerful forcing agent, and it also lasts far longer in the Earth's atmosphere. It is relatively twice as powerful as the next major forcing greenhouse gas, methane, and relatively ten times as powerful as the third, nitrous oxide. Carbon dioxide alone contributes up to 12% to the greenhouse effect. It is an end product in organisms that obtain energy from breaking down sugars, fats and amino acids with oxygen as part of their metabolism, in a process known as cellular respiration. This includes all plants, animals, many fungi and some bacteria. (Some contribution that cannot be avoided, so, we have to offset it by planting trees, which are absorbers of Carbon dioxide)
Mehtane: This is a relatively potent greenhouse gas with a high global warming potential (i.e., warming effect compared to carbon dioxide). When averaged over 100 years each kg of Methane warms the Earth 25 times as much as the same mass of Carbon dioxide. The total warming effect of Methane is smaller than that of Carbon dioxide, since there is approximately 220 times as much Carbon dioxide in the Earth's atmosphere as Methane.
Ozone: The contribution of this gas is difficult to predict as it is not present uniformly across the earth. However, recent scientific review on the climate change suggests that the radiative forcing of tropospheric ozone is about 25% that of carbon dioxide.
Other gases: Halocarbons and nitrous oxide are also contributors to the green house effect but they are not too significant.
Forcing Agent:
Forcing agents are gases (in our case here) that help in forcing (or radiative forcig). Radiative forcing is defined as the difference between the incoming and the outgoing radiation energy in a climate system. A positive forcing warms up the system while a negative one cools it down.
Carbon Footprint:
A representation of the effect human activities have on the climate in terms of the total amount of greenhouse gases produced (measured in units of carbon dioxide).
More info can be found at:
1 comment:
Carl Sagan's book, Billions and Billions, contains two excellent chapters describing the science and politics of global warming and stratospheric ozone depletion.
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