This article by Richard J. Petschauer at Watts Up With That? is an excellent short introduction to the views on climate that are held, generally, by those described as skeptics. (I prefer to call them climate realists.) You should read it all, but here are some excerpts:
There are many areas where most skeptics and the “alarmists”, as they are called, agree. First is the idea of “climate sensitivity”, a useful benchmark for making estimates. It is the final average global temperature rise that would be caused by a doubling of the carbon dioxide (CO2) in the atmosphere, assuming there are no natural changes. Second, most agree on well established methods to estimate how greenhouse gases absorb and emit heat, and that doubling of CO2 will reduce the heat leaving the planet by a little more than 3.5 watts per square meter. This compares to both estimates and satellite measurements of the total now leaving of about 235 watts per square meter. … A 1% change in energy from the sun or a 7% change in cloud cover would cause about the same change as doubling CO2. Third, there is general agreement on how much the average surface will warm to make up for this heat loss: about 1 C (1.8 F). But here is the rub: this estimate is before the atmosphere and the surface, including oceans, react to this temperature change.
How the climate reacts to the initial warming is the main area where most skeptics have problems with the IPCC and others. These reactions are called “feedbacks”. Positive ones amplify any temperature change (warming or cooling from any cause, not just from CO2). Negative ones diminish a change. … The major disagreements are the magnitudes of the feedback values and for clouds, even if it is positive or negative. The final IPCC warming estimates for doubling CO2 range from 1.5 to 4.5 C. The skeptics have no common voice, but their values range from about 0.5 to 1.2 C, a significant reduction. IPCC also uses a 1% annual growth of the CO2 content in the atmosphere, while data shows only about 0.55%.
Alarmism is based on models, not observation, which is the fundamental reason why it is bad science.
One primary complaint is the IPCC and most government funding research have abandoned improving the simple energy balance model and the feedback concept and gone to complex climate models that try to estimate many conditions across the globe and layers in the atmosphere over many years and then a temperature change. Small errors can propagate into unknown large ones. There are over 100 of these models written by different teams and their results differ by a range to 3 to 1. And nearly all overestimate warming compared to observed data. This is settled science? No! And it is bad engineering practice, which some scientists apparently don’t understand, to try to solve such a complex problem without breaking it down into smaller steps that each can be verified and corrected. …
We believe the complex computer models’ overestimation of warming is mostly based on a combinations of three factors: overestimating positive water vapor feedback, underestimating negative feedback from increased sea surface evaporation and treating cloud feedback as positive feedback while it is very likely negative. [T]he models estimate a value of positive feedback for clouds only because this amount is needed to boost the initial 1 C prefeedback warming up to the models’ final average estimate. It is more likely that more evaporation and water vapor will increase cloud content, a net cooling effect. Using simple energy balance models with proven greenhouse gas absorption/radiation tools, the result of these changes indicates a warming from double CO2 in a range of 0.6 to 0.9 C, much less than IPCC’s value of 1.5 to 4.5 C.
The modest warming that can realistically be expected will in all probability be a good thing.
About 1 C warming in the next 140 years does not seem to be a problem. (It will actually take longer because the ocean heat storage will delay the warming). Furthermore, both simple models and data show that most of the warming will be in winter nights in the colder latitudes. … An example is in Minneapolis, Minnesota at 45 degrees latitude. About half of July record highs were set in the 1930s, with only 3 since 2000. However 80% of the record January lows were from 1875 to 1950. This winter warming is a benefit. And what makes people think the climate around 1900 represents the ideal? In 2014 we just saw a very cold winter, typical of that era. Finally, warmer temperatures increase evaporation and precipitation and since CO2 is a plant food, food crop production will increase, contrary to some other estimates.
When models conflict with observation, observation wins, and the models need to be corrected.