I'm for going green.
A question for the Anthropogenic Global Warming 'skeptics': Why are you against the idea that man could possibly be causing the environment to change via an increase of greenhouse gases? Do you think it's a huge conspiracy to make certain people rich? Denial of anthropogenic climate change, to me anyways, is similar to denial of evolution. That being there is scientific evidence out there that fully backs it but there are groups that still deny it is occurring. Al Gore, as was mentioned in this thread, did not come up with the theory of global warming. In roughly 1824 Joseph Fourier discovered the greenhouse effect and in 1896 Svante Arrhenius was the first to calculate that absorption properties of CO2 and water vapour would increase the heat content of the atmosphere. It all comes down to an increased trapping of infrared radiation near the surface of the planet and a heightened greenhouse effect.
Let me explain how this works. Kirchoff's Law of Thermal Radiation states that any object of non-zero temperature, or 0 kelvin, will emit radiation while Planck's Radiation Law states that that emitted radiation will vary in wavelength dependent on the temperature of the emitting object. Solar energy that strikes the Earth originating directly from the Sun is therefor in a shorter wavelength. These wavelengths include much of the ultraviolet, visible and infrared spectrums. This energy strikes the surface of the planet if it isn't first absorbed or deflected via a process known as global dimming, caused by atmospheric aerosols such as sulfur dioxide, or surfaces with high albedo, such as snow. When this solar energy strikes the surface of the planet it is absorbed by that surface and released as heat radiation in the infrared in a longer bandwidth than the output from the Sun due to the differences in temperature. This infrared radiation travels back up through the atmosphere on it's way into space, however there are properties in certain gases, collectively known as greenhouse gases, that can absorb specific wavelength of radiation and re-emit that radiation in all directions, 50% of it upward and 50% of it downward. You often hear skeptics state something like "CO2 is already saturated". It doesn't matter if it's saturated at lower levels because there is still that 50% of the original 100% that was re-emitted by that first greenhouse gas molecule that can still be reabsorbed by another similar molecule and the process continues until that energy eventually does reach space. The 50% that is released downward back towards the surface of the Earth, if it isn't again absorbed by another similar molecule, will be reabsorbed by the surface of the planet and increase it's heat content in addition to the direct solar energy being absorbed from the Sun.
As you increase the amount of greenhouse gases in the atmosphere you also increase the amount of infrared radiation being trapped in the troposphere, as explained above. Atmospheric greenhouse gases have risen within the past few centuries. The main human emitted ones are CO2, which has risen from roughly 280 parts per million to over 390 parts per million in the last two centuries, and methane (CH4) which has risen approximately 130% in the past century. CO2 is released when fossil fuels are burned and oxidized while methane is released through ruminant beltching and flatulence due to feed type. The total annual emissions of anthropogenic CO2 amount to about 30gt. As fossil fuel use has increased the rate of increased atmospheric CO2 concentration has increased as well. In 2009 alone there was approximately a 2 part per million increase in CO2 concentration. 1 part per million is roughly equal to 7.5gt of CO2. Simple math shows that the total increase of atmospheric CO2 amounts to 15gt, half of what the total anthropogenic emissions are. The other half of that CO2 that is not in the atmosphere is being taken up by carbon sinks, mainly the ocean which is the largest carbon sink in the world. As you increase the amount of CO2 in the ocean you also increase it's acidity. The pH value of the ocean is currently falling as the rate of CO2 uptake has increased making it more acidic as opposed to more alkaline. You often here skeptics attribute the growing temperatures, roughly 0.7C in the last 2 centuries, to the Sun. The Sun's output has actually declined for the last 40 or 50 years. If it was specifically due to the Sun we would be cooling now, which we are not.
You often hear skeptics reasoning for not acknowledging anthropogenic climate change or global warming because the climate has changed in the past. They say things like there were ice ages in the past or it has been warmer in the past. However it is known that there are more forcings than greenhouse gases, which historically work as a feedback and not a forcing, such as albedo, lapse rate, atmospheric aerosols, variations in ocean circulation, Milankovitch Cycles, and so on. Temperature fluctutions of the past are mainly attributable to Milankovitch Cycles, or orbital eccentricity and changes in axial tilt, of the planet. You also hear them state things like "Other planets in the solar system are warming" as the reason for disbelief. However, each planet has it's own seasons, Milankovitch Cycles and atmosphere. Out of the over 150 bodies in the solar system only 8 of them are known to be warming and actually several, such as Uranus, are cooling. The reasons for the warming of most of the planets and moons, save for Pluto, are known, such as the dust storms on Mars, the changing seasons on Neptune or the gravitational effect Jupiter has on Io. This is another attempt at attributing the warming to the Sun using bad science.
Evidences for anthropogenic global warming abound. You can click on the links below to see some of these evidences, as provided by peer reviewed literature.
Outbound infrared radiation is decreasing at greenhouse gas wavelengths
Downward infrared radiation is increasing at those same wavelengths
The stratosphere is cooling while the troposphere is warming - http://acd.ucar.edu/~randel/SPARC_revised.pdf - (Note that as you increase in altitude through the troposphere, the mesosphere and the thermosphere the decrease in temperatures becomes stronger indicating it can not be due to the Sun but has to be an internal forcing)
The tropopause is increasing in altitude and the troposphere is getting larger - http://www.sciencemag.org/cgi/content/abstract/sci;301/5632/479
If you forgo what I stated before concerning the amount of annual atmospheric CO2 increase compared to the total human annual emissions you could still explain this as "Well it's getting warmer" because as temperature increase so does CO2 outgassing via the oceans. There are human fingerprints in the carbon itself that form the carbon dioxide to show that, indeed, it is due to the burning of fossil fuels. Thereare numerous different types of carbon in existence, each with a different number of neutrons. Cacrbon-12 is the most abundant and makes up to 98% or 99% of the atmosphere, carbon-13 is the second most abundant and makes approximately 1% of the atmosphere while carbon-14, which many of you will know is unstable and used for carbon dating, is a trace gas. Plants, from which fossil fuels are made, have the ability to differentiate between these different forms of carbon based on their molecular weight. Plants contain a 2% different ratio of carbon-12 to carbon-13. Therefor if the increase in CO2 is due to the burning of fossil fuels we should see the fingerprint in the carbon isotopes that make up the CO2. And this is exactly what we see. Over the last 150 years the ratio of atmospheric C12 to C13 has increased by about 0.15%.
Atmospheric C12 to C13 ratio change between 1978 and 2000 - http://cio.eldoc.ub.rug.nl/FILES/root/2005/EcolStudKeeling/2005EcolStudKeeling.pdf
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