Can a 3% increase be opposed by some other effect (natural forcing, statistical noise, etc.)?
This is yet another case of the innumerate American.
“3%” sounds like a small number, but in all sorts of complex systems what sounds (to the uniformed) like a small number turns out to be very critical.
For example, take finances. Let’s say you’re going to buy a house that costs $300,000. To qualify for a loan you have to put down $30,000. However, you only have $29,000. That’s only 3% away…. yet the bank doesn’t care it’s “only 3%”, they still won’t go through with the deal. I remember when I bought my last house I needed to borrow a few dollars from a relative to make up such a difference, so I know it can happen.
Back to the proposition of the OP - besides a case of innumeracy, it is a failure to understand physics. There is no “conservation of human perceptions about percentages” in thermodynamics. Rather, there is Conservation of Energy. The changes made by adding CO2 to the atmosphere affect the flow of energy from the Earth to space, and the net temperature of the Earth’s surface changes (rises in this case) while the Earth seeks equilibrium with the space surrounding it.
Spencer’s web article is just another attempt (there are many) for him to publish his view (rejected by his peers) that the positive feedbacks of doubling CO2 in our atmosphere are trivially small. His examples are chosen to mislead, also. His distinction between “natural” and man-added CO2 is artificial.