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I know there is global warming, and I know that it is caused by human activity, but is carbon dioxide the cause of it? I read somewhere that apparently increase of CO₂ doesn't cause the increase in global temperatures, but rather, global temperatures cause the increase of CO₂. Can someone verify or disprove this claim?

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How do you know that humans have caused global warming if you doubt that CO2 is behind it? –  Andrew Grimm May 20 '11 at 12:45
    
Is this essentially a duplicate of skeptics.stackexchange.com/questions/41/… –  Andrew Grimm May 20 '11 at 15:39
    
Humans can cause Global Warming through other means. –  Thursagen May 21 '11 at 3:00
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It depends what you mean by cause and how far you want to trace the effects (even if you accept the consensus on warming). Higher CO2 doesn't directly account for the majority of projected warming in models: most warming comes from other forcing effects such as higher water concentrations and other feedbacks. So even in standard climate models it isn't the CO2 that directly causes the warming. –  matt_black Jul 17 '12 at 10:47
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Do note that you have a false dilemma. It's also possible that carbon dioxide in the atmosphere increases the global temperatures, AND an increase in global temperatures increases the amount of carbon dioxide in the atmosphere. What a nasty feedback loop that would be... –  Kaz Dragon Jun 3 '13 at 12:24

3 Answers 3

up vote 13 down vote accepted

The Earth’s greenhouse effect is a natural occurrence that helps regulate the temperature of our planet. When the Sun heats the Earth, some of this heat escapes back to space. The rest of the heat, also known as infrared radiation, is trapped in the atmosphere by clouds and greenhouse gases, such as water vapor and carbon dioxide. If all of these greenhouse gases were to suddenly disappear, our planet would be 60ºF (33ºC) colder and would not support life as we know it. Human activities have enhanced the natural greenhouse effect by adding greenhouse gases to the atmosphere, very likely (greater than 90 percent chance) causing the Earth’s average temperature to rise. These additional greenhouse gases come from burning fossil fuels such as coal, natural gas, and oil to power our cars, factories, power plants, homes, offices, and schools. Cutting down trees, generating waste and farming also produce greenhouse gases.

Source: The Environmental Protection Agency (EPA)

http://www.epa.gov/climatechange/fq/science.html

You may also want to read:

http://www.epa.gov/climatechange/science/stateofknowledge.html

This page acknowledges the gaps in scientific climate knowledge, and differentiates fact from speculation/uncertain predictions.

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Global WarmingSource


Carbon Dioxide:

Carbon dioxide is one of the greenhouse gases.

When its atoms are bonded tightly together, the carbon dioxide molecule can absorb infrared radiation and the molecule starts to vibrate.
Eventually, the vibrating molecule will emit the radiation again, and it will likely be absorbed by yet another greenhouse gas molecule.

Carbon Source

This absorption-emission-absorption cycle serves to keep the heat near the surface, effectively insulating the surface from the cold of space.

Here are some research papers on the absorption properties of CO2.



From John Cook:

In 1970, NASA launched the IRIS satellite that measured infrared spectra between 400 cm-1 to 1600 cm-1.
In 1996, the Japanese Space Agency launched the IMG satellite which recorded similar observations.

[Harries 2001] compared both sets of data to discern any changes in outgoing radiation over the 26 year period.

What they found was a drop in outgoing radiation at the wavelength bands that greenhouse gases such as CO2 and methane (CH4) absorb energy.

The change in outgoing radiation was consistent with theoretical expectations.
Thus the paper found "direct experimental evidence for a significant increase in the Earth's greenhouse effect".

This result has been confirmed by subsequent papers using data from later satellites (Griggs 2004, Chen 2007).


Simply put:
Satellites measuring infrared (heat) radiation coming from our Earth found that CO2 (and other greenhouse gases) won't let it escape into space.

Greenhouse effectSource

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Without preliminary explanation it’s not clear how the infrared spectra are relevant, and hence how the first citation is relevant (so I’m suggesting modifying the order of your explanation a bit). –  Konrad Rudolph May 20 '11 at 14:49
    
@Konrad- took your critizism to heart and restructered my answer –  Oliver_C May 20 '11 at 15:28
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Ooooh, pretty pictures! –  KitFox May 21 '11 at 0:58
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in regards to the picture, why don't the greenhouse gases stop the heat from entering the atmosphere? –  msmucker0527 Jun 24 at 15:30
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@msmucker0527: because CO2 is largely transparent to visible light. Light comes in as visible light, gets absorbed by the surface and re-emitted as infrared, and can't get out. The atmosphere is a partial one-way door for energy. –  Jon of All Trades Jun 24 at 17:59

A rather late answer on this question, but here goes: The idea that "global temperatures cause the increase of CO2." is fairly easily refuted. The line of reasoning is that the solubility of CO2 in water decreases as temperature increases, so the rise in global temperature implies that the oceans will have released some of the dissolved CO2 that it contains. The premise is correct, but the conclusion is a Non sequitur as it ignores the fact that the solubility of CO2 in water also depends on the difference in partial pressure of CO2 between the ocean and the atmosphere. As we have released CO2 from fossil fuels into the atmosphere, the partial pressure of CO2 in the atmosphere has risen, and so the oceans have been taking up more CO2, not less.

How do we know this is true? . The argument is easily refuted by the observation that the rate at which atmospheric CO2 levels are rising is less than the rate at which we are releasing CO2 into the atmosphere from fossil fuel use, which implies that the natural environment must be a net carbon sink, taking in more carbon each year than it emits.

More formally, let Ea represent annual carbon emissions from anthropogenic sources (fossil fuel use and land use change), En represent the carbon emissions from all natural sources (the oceans, soil respiration, volcanos etc.) and Un represent the uptake of carbon by all natural carbon sinks (oceans, photosynthesis, etc.), Ua would be the uptake of carbon due to anthropogenic activities, but this is essentially zero, so we can safely exclude it from the analysis. Then assuming that the carbon cycle obeys the principle of conservation of mass (any carbon emitted into the atmosphere that is not taken up by natural sinks remains in the atmosphere), the annual change in atmospheric CO2 is given by:

C' = Ea + En - Un

This can be rearranged to give an estimate of the difference between annual emissions from all natural sources and annual natural uptake by all natural sinks.

En - Un = C' - Ea

We have accurate, reliable data for the growth of atmospheric CO2 and for anthropogenic emissions (for details, see Cawley, 2011). Both of these are displayed below, along with an estimate of the net natural carbon flux En - Un. The fact that the net natural flux is negative clearly shows that natural uptake has exceeded natural emissions every year for the last fifty years at least, and hence has been opposing, rather than causing the observed rise in atmospheric CO2.

enter image description here

source

Some time back, I wrote a journal paper refuting a related climate myth, which outlines some of the evidence that the rise in atmospheric CO2 is anthropogenic, and is not a natural phenomenon.

Gavin C. Cawley, "On the Atmospheric Residence Time of Anthropogenically Sourced Carbon Dioxide", Energy & Fuels, volume 25, issue 11, pages 5503–5513, 2011.

I find it hard to understand how this argument can be so ubiquitous on climate blogs, given that it is so easily refuted. For further information, see the many articles on SkepticalScience.com addressing this issue (and other climate myths).

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@jwenting In case you hadn’t noticed, you’re talking to one (AGW believer, that is). :p – Also, nobody got banned yet for posting facts here so stop spreading demonstrable falsehoods. Heck, we didn’t even block Christopher Monckton, despite him being known for lying through his teeth on the subject. –  Konrad Rudolph Sep 12 '13 at 10:34
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I wouldn't characterise myself as an "AGW believer", I just try to understand the science (and check out claims to see if the data actually do support the claim, which is how I ended up writing a paper for Energy and Fuels). I generally find that mainstream climatologists are rather better supported by the evidence than extremes on either side. –  Dikran Marsupial Sep 12 '13 at 11:09

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