[badpun]

> _All_ the studies are measuring the same tendency : the temperature is rising.

Are you talking about predictions (and not measurements, you don't need a model to measure temperature)? Assuming you are, there's unfortunately a huge problem with modeling (and heavy math and stats-based science in general), in that researchers tend to stop looking for bugs in the model when it returns the results that they expect. In other words, if a bug in the model tells the researcher that Earth's temperature will decrease by 4 C by 2100, he will look over the model until he finds the bug, but if the model tells him that the temperature will increase by 2 C, thus confirming his inner bias, he'll declare it correct and move on to writing a paper based on the "finding".

Alternatively, as a thought experiment, imagine if math research were done in the way climate science is done. We would have proofs that are millions of pages long and were never verified by anyone. We would trust in them only because the author says that they are correct. Is this science?

[magic-chicken]

A given prediction can be wrong, an experiment may be biaised, my point is that you choose to ignore that the vast majority of the experiments and measurements point in the same direction.

>>Researchers tend to stop looking for bugs in the model when it returns the results that they expect.

Again... they are _ALL_ biaised ?

[badpun]

It's not impossible - groupthink (https://en.wikipedia.org/wiki/Groupthink) has happened many times in the past among supposedly most brilliant minds.

Also, how many independent, comprehensive models (with codebases) for global climate change are there in the science world?

[canhascodez]

Could you perhaps indulge me by describing the action of CO2 in the atmosphere, as you understand it?

[_up]

Can you explain why 300ppm CO2 is totally normal and fine, but 400 ppm (Parts per Million) CO2 in the Atmosphere basically means the world is doomed?

[canhascodez]

I'd be more than happy, but it would help if you answered my question, so that I can more effectively address your concerns.

[_up]

CO2 produces a greenhouse effect by absorbing IR. This alone doesn't prove that Industrial produced CO2 alone is this time mainly responsible for climate change. All the other times' science believes the climate changed because of sun intensity.

[dragonwriter]

> All the other times' science believes the climate changed because of sun intensity.

False. Lots of past climate changes were due to changes on Earth and its atmosphere (and sometimes, specifically, life on Earth), not changes in solar output (e.g., notably, the Huronian glaciation believed to have resulted from the Great Oxygenation Event, which resulted from the exponential growth of photosynthetic life.)

[canhascodez]

Solar intensity has increased slightly over the last few billion years, but previous changes in climate have been driven primarily by Milankovich cycles, volcanic emissions, and plate tectonics.

That the post-industrial rise in atmospheric CO2 is of anthropogenic origin is hopefully not a point of dispute, but it is demonstrable if necessary. Thus it remains to show that this must raise the equilibrium temperature. So, as you say, CO2 selectively absorbs outgoing IR. In the lower atmosphere, this actually does not have as much of an effect as you might think. Water vapor blocks quite a bit of the absorption spectrum, and the effect of CO2 is more-or-less saturated already.

The mean free path of an outgoing IR photon in the lower atmosphere is quite short. Absorbed photons are re-emitted in a random direction, but take an overall upward course, the mean free path rising with altitude. At the (radiative) top-of-atmosphere, the mean free path is infinite: the photon is more likely to leave Earth. At the edge of space, there is essentially no water vapor, so the action of CO2 is greater. The effect of increasing the amount of CO2 in the atmosphere is to push the CO2-dense region of the atmosphere further out into space. Photons must take a longer path out of the atmosphere, and this must raise the overall temperature of the Earth proportionally, specifically by 3.7 W/m^2 per doubling of CO2, which is commonly held to be equivalent to 1 degree C of global temperature. This must be the case unless our understanding of thermodynamics is very wrong (and if you have an issue with thermodynamics then you have some pretty serious issues).

So, one degree C ain't so bad, right? Well, it wouldn't be if that were it. However, there are several problematic feedbacks. One is that melting a lot of ice lowers the Earth's albedo, which causes it to absorb more heat. Another issue is that there is a lot of this "water" stuff around, which is very readily absorbed by the atmosphere, in a manner that increases very sharply with temperature. Water vapor is a much better greenhouse gas than CO2 by all accounts.

Climate science is not an extrapolation from the temperature record. There is a solid minimum bound on the temperature effects of doubling atmospheric CO2, and a variety of amplifying positive feedback effects. So far, in the last twelve decades, we have not managed to find anything which would reduce those effects to something manageable. At this point, the effect would need to be both very large, in order to offset the strong H2O feedbacks, and very small, to not have been noticed. The most plausible option would be "something poorly understood about the H2O feedbacks". I believe the most successful of such theories would be Dr. Richard Lindzen's Iris Hypothesis, which has generally failed to find support. At this point, there are no particularly plausible mechanisms which would transfer this extra energy to space, and if those did exist, then they would not necessarily be a non-issue: even if thermodynamics and optics are entirely wrong, the planet is warming, and we will have to deal with that even if it can't be prevented.

If you have any other questions, or would like citations for any of the above, do feel free to ask.

[magic-chicken]

Can you explain why a healthy body temperature is about 98F and why you can die if it gets too far from that ?

[femidav]

Can you explain what caused ice ages? 10K rises and falls in few years?

[canhascodez]

Glaciation is most strongly dependent on Milankovich cycles:

  - https://en.wikipedia.org/wiki/Milankovitch_cycles
  - http://www.indiana.edu/~geol105/images/gaia_chapter_4/milankovitch.htm

Plate tectonics and volcanic activity have also influenced climate in the past, e.g. the closing of the Panamanian isthmus, or the formation of the Deccan Traps.

Interestingly, the original paper proposing AGW (in 1896) was actually intended to explain Ice Ages:

  - http://www.rsc.org/images/Arrhenius1896_tcm18-173546.pdf