If by "climate models," you mean computer simulation models, absolutely not. Indeed, the proof that carbon dioxide causes global climate change does not depend at all upon such models (as useful as they clearly have been to a whole range of research investigations for decades). Fourier and Arrhenius figured out the greenhouse effect long before digital computers were developed, and the theoretical and instrumental proof of their theories was based on data and scientific knowledge, not on projections. In fact, such projection models have been shown to be quite accurate when compared to actual data, but the key findings of climate science have been solidly established for decades and quite independently of any such modelling:

U.S. National Academy of Sciences, 2010:

http://books.nap.edu/openbook.php?record...

“Climate change is occurring, is caused largely by human activities, and poses significant risks for a broad range of human and natural systems.”

http://www8.nationalacademies.org/onpine...

“Choices made now about carbon dioxide emissions reductions will affect climate change impacts experienced not just over the next few decades but also in coming centuries and millennia…Because CO2 in the atmosphere is long lived, it can effectively lock the Earth and future generations into a range of impacts, some of which could become very severe.”

http://www.physics.fsu.edu/awards/NAS/

“The Academy membership is composed of approximately 2,100 members and 380 foreign associates, of whom nearly 200 have won Nobel Prizes. Members and foreign associates of the Academy are elected in recognition of their distinguished and continuing achievements in original research; election to the Academy is considered one of the highest honors that can be accorded a scientist or engineer.”

If, on the other hand, you mean models in a general theoretical sense, then nothing in climate science or any other science is proven absolutely. Even gravity is just a theory based on a model with equations.

Carbon dioxide increasing global temperatures is pretty well established. The problem is the models include estimates for clouds that are not as well grounded in physics. They basically assume that clouds formed by warming will cause even more warming, when the effect could be the opposite. IPCC reports will acknowledge some uncertainty with regards to clouds, but then ignore the detail that the models basically use one direction only. Without this assumption, the amount of global warming seen in the models is small.

Depends on what you mean by 'appreciably'. Some basic physics theory suggests that CO2 will cause planetary temperatures to rise by about 1 degree Celsius. Models and feedback theory are needed to achieve higher numbers.

I haven't seen anything to suggest that CO2 would decrease temperatures.

Climate models are only as smart as those who program them. No one on earth knows enough about the environment to properly program them.

Quote by Chris Folland of UK Meteorological Office: “The data don't matter. We're not basing our recommendations [for reductions in carbon dioxide emissions] upon the data. We're basing them upon the climate models.”

Quote by David Frame, climate modeler, Oxford University: “Rather than seeing models as describing literal truth, we ought to see them as convenient fictions which try to provide something useful.”

Like Mr. Frame says, they are fiction. It is a tool to get at the truth but we have a long way to rationally get there.

Notice: Mr Frame, a proponent of AGW, says they are fiction. Still Gary F believes in them even though they have been proven wrong by the earth itself. I'm sure he believes in the Easter Bunny and Santa Claus.

change is a hypothesis, and climate models are a means of predicting the outcome of this hypothesis or theory, however whilst the science is good, there are so many natural effects that could alter the results, such as clouds, evaporation, water vapor etc.

I believe climate models have been validated against past climate, but as for predicting future climate changes they are not doing at all well.

Climate models are mathematical experiments based on observations and measurements of empirical (real-world) data.

>>Have these models been validated against data?<<

Yes. All models are validated before they are ever used. Validation is a process of model evaluation that compares the fit between model values and observational data.

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OM --

They use the word "evaluation" - however, they are talking about "validation" (as opposed to, say,"verification").

http://www.ipcc.ch/publications_and_data...

No reality always proves them wrong , They cannot predict the climate in 2100 or

2200 .

They always show the worst outcome and not the other runs when nothing happened at all .

@Gary F

Could you please point me to the section of the latest IPCC AR4 report where they discuss model validation?

I started with this chapter of WG I but could not find a single mention of the word validation: http://www.ipcc.ch/pdf/assessment-report...

Yeah obviously.

Are the climate models the only "proof" that human produced carbon dioxide causes global temperatures to rise appreciably? Do the climate models contain equations that will only cause temperature predictions to increase with increasing levels of carbon dioxide (can temperatures decrease with increases in CO2)? Have these models been validated against data?