There is some confusion as to sanity of global warming sceptics. I present a possible logic. I will begin by explaining what global warming is and why many people believe it is true. Then I will posit three reasons why people would be sceptical: two technical and one psychological which combined give a logical reason to be sceptical of global warming.
At the heart of the global warming argument is an energy balance relation. This is the famous second law of thermodynamics which states the energy gain (loss) of a system is equal to the net flow of energy into (out of) a system. Among all scientists and engineers there are none who doubt it. It is a fundamental assumption and nearly 200 years of experimental testing have never shown it to be wrong. At the basic level global warming then says the energy which comes into the earth is greater than the energy that leaves the earth. Therefore the temperature of the earth increases because temperature is directly correlated with energy.
The primary energy source is solar radiation mostly in the visible light range. Some of this light is absorbed by the earth and much of it is reflected away. The primary mechanism for heat leaving the Earth is through infrared radiation. And carbon dioxide (and other greenhouse gases) naturally absorbs infrared radiation very well The absorbed radiation is then reemitted but in a random direction, so a little more than half is reflected back to earth. It follows that if the carbon dioxide percentage or volume of the atmosphere increases we will increase the amount of energy in the earth.
There are of course secondary effects, and research has included them into their models as shown by this Bloomberg animation and the results are well correlated with data.
There are three reasons to be sceptical of this model. The people involved are biased. The observational data is less trustworthy than put forth. There is lots of unresolved uncertainty in the models.
The people who conduct research in climate change have a huge interest in wanting to continue funding study of climate change. It is how they feed their families. Funding agencies have an incentive to fund to only the most important research because that is how they increase the amount of money they control and it increases their prestige and status. When you couple these things together, you end up with the ability to hijack science. Such claims have been made. My father, a PhD chemical engineer, knows one scientist who didn’t privately believe in climate change but would publicly believed in order to strengthen his proposals. Finally the nature of selling suggests that many people will exaggerate the importance of their research in order to get funding. This is going on to some extent, but it would be unclear as to how much. The significance, could be negligible but it could also create a systematic bias.
The second reason to doubt climate change is you don’t trust the data. Not necessarily that it has been manipulated, but rather that we cannot obtain an adequate estimate for the average global temperature. I am not questioning the methods used by scientists but there is a wide range of uncertainty in the data leaves the data suspect. Our land based stations (especially in the US) do a reasonable job of covering the entire land but oceans covers three quarters of our surface. And this is where there are issues. There is neither good coverage of the oceans nor precise locations of measurements. In the experimental data, this error analysis is lacking (specifically because it makes the results less obvious). As we move into the digital age the data is definitely better, but there are still open questions on how the old data compares to the actual value. While, we have tools to estimate the uncertainty in the data, it is never presented with this uncertainty (because it makes the case for climate change weaker).
The final reason to doubt is lack of trust of the models. While the models match data very well, there are still open questions in it’s usefulness in predicting the future. In my day job, I do mathematical modelling. Mathematical models are easy to match data if you throw in enough parameters. Just because you can get the model to match data, doesn’t mean that it matches reality. What is really difficult is to get models which you can successfully calibrate to match future data. The best test that these models match data is whether or not they can predict future climate changes (over 10-20 years). As of now the validation of the models for prediction has yet to occur (due to the length of time needed). The large number of parameters and complexity of the model leads one to question its ability in spite of getting the fundamental physics right. That is I believe, with time, I could tweak the model and parameters in a way that matched data and showed minimal human effect without fundamentally altering the agreed upon physics. Academia (and science) has long had a weakness in dealing with complex systems which cannot be broken down into simple systems that can be individually tested and global warming fits very neatly into this category.
The argument against climate change then goes like this. Scientists who believed that human interaction was a significant cause naturally (without intent to abuse science) developed constitutive laws and selected parameters which were likely to match their initial assumption. The scientists who did this were more likely to find continued fund while the ones who didn’t primarily were likely to lose funding. Thus the results are skewed towards showing a greater dependence on humans than what is naturally the case. These results have not been corrected because the time needed for predictive testing has not passed. Additionally they continuously add more complexity to the model to account for additionally effects which gives them the permanent ability to never have to admit the model is wrong .
Personally, it seems that climate change has a stronger case than the deniers, but I think climate change denial can be an intellectual pro-science position. Finally I believe that the government and it’s people have a responsibility to be good stewards of the land and much of the funding done under global warming prevention should be done because it is being good stewards of the land. As Jesus once said, wisdom is justified by all her children. Time will let us know who is right.