Positive feedback increases the effect of a change in the inputs. It’s deliberately designed in mostly when stability is not desired. Some early single-vacuum-tube radios deliberately used positive feedback to increase the gain above what was possible in a single well-stabilized stage, but you had to keep tweaking the adjustments on those to keep them working…

The CO2 issue is more complex than what Adiran and Pieter noted. Even if we assume that CO2 is a ‘warming’ gas in the atmosphere, its impact is small compared to water vapor (which, based on greenhouse studies, has 20 times the warming effect because of better solar heat absorption and higher concentration). Methane is also a ‘warming’ gas, but its concentration is too low to have any significant impact on global temperatures.

The positive feedback discussion by the IPCC and by Warren Meyer irks me. First, positive feedback is a psychology term about how an organism responds to good (positive) stimuli. The term the IPCC really wants is something like multiplicative effects or potentiation (when two or more things combined give an effect that is multiplicative rather than additive, such as ethanol and barbiturates). But, in chemistry and physics, examples of multiplicative effects are rare. The IPCC models are so bad that they can essentially apply their forcing factors to anything (too many people hopping on one foot) and claim it relates to global warming. I trust nothing from the IPCC, because the group is about keeping itself funded and influential with governments. The IPCC is not about climatology.

I don’t agree with your conclusions, but I think you’ve set out the issues excellently. Clearly, human activity has increased the amount of CO2 in the atmosphere, and the chemical properties of CO2 mean that its increased concentration will lead to warming. As you said, the question is how strong is this effect and how will this interact with other effects in the atmosphere.

I’ve not studied the IPCC report as carefully as you, so I was interested to learn how much heating is directly attributable to CO2 alone. I am curious that you don’t mention anything about other green houses gases, like methane. Are these also ignored in the IPCC report?

Without much experience in this subject, given that there was an ice age just 10,000 years ago, or so, I would expect that the climate was fairly unstable. On face value I’d be willing to accept the possibility that there is a positive feedback system and that it could be quite strong. On the other hand, if the evidence is as weak as you said, it’s shocking the IPCC hasn’t made resolving this issue a priority.

The “Greenhouse Effect” is misnamed, and has nothing to do with greenhouses. Greenhouses eliminate convection – that is, they eliminate windchill (or windwarming, in situations where the ambient temperature is higher than an entity-specific temperature – not a common natural situation on Earth). The “Greenhouse Effect” itself is that the atmosphere re-absorbs blackbody radiation and particularly infrared light (99% of all “heat” you feel radiated by something is actually infrared light – warmth radiates directly much more slowly.) In essence, the atmosphere captures a percentage of the heat leaving the planet in the form of infrared light. It isn’t debated that adding CO2 increases the percentage of that heat which is captured – what is debated is precisely how much heat is captured (The variance in the figures is greater than the figures themselves), and what effects, short and long term, that change in percentage will have.

The climate is not static – adding CO2 will change it, in a number of complex ways. (One of these ways is that plant growth can increase – which both captures additional CO2, and decreases the quantity of heat, as the plants capture and sequester some of that energy as well.) The question is precisely what kind of change, and the significance.

There’s also the question of internal variability – none of the geological-term planetary records has precision on the order of decades, and data points represent (practical) averages over many many years. There is absolutely no reason to believe current trends are even exceptional, and needing particular explanation.

But primarily-solar forcing has no better evidence going for it than primarily-CO2 forcing. If you wish to be skeptical, be skeptical – don’t select one concept as a pet theory to be protected, as our opponents do.

It is silly to argue whether CO2 in the atmosphere can cause global warming: It clearly does.

No well-designed studies have shown that changes in the amount of atmospheric carbon dioxide cause global temperature changes. The greenhouse effect is just that: certain gases cause higher temperatures in a sealed, moist, warm room with walls, roof, and floor made of impermeable materials. In those conditions, water vapor and carbon dioxide concentration changes cause temperature changes (when all other factors are held constant).

To claim that the earth is the same as a greenhouse is just ridiculous. The earth has no roof and no walls. Instead of an impermeable floor, most of the earth is covered by water which can absorb or release carbon dioxide. Ice core records have shown that during past periods of warming, carbon dioxide concentrations were higher. But, was that cause or effect? Warmer water holds less carbon dioxide (that’s why warm soda goes flat faster than ice cold soda). So, if increased solar output caused warming (between those long eons known as ice ages), then one would expect as a direct effect that water CO2 would decrease and atmospheric CO2 would increase.

I believe (but cannot prove) that we are in the midst of a short period of global warming caused primarily by increased solar output. I am too skeptical to believe that CO2 from burning oil and coal is changing the climate.