Mr. Hohenberg presents a very impressive list of Professor Happer's credentials, including that he is a "critical thinker, a real scientist who follows no one but takes the paths where true science leads." Let's see examples of credentials and being a critical thinker who follows his version of where true science leads. "Heavier than air flying machines are impossible": Lord Kelvin when he was president of the Royal Society; not bad credentials. In 1884, a PhD student wrote his thesis on his idea that electricity passing through solutions could best be explained if one supposed that atoms or molecules could break up into electrically charged fragments called "ions"; his professors were convinced he was wrong; the student barely passed. (He received a Nobel Prize for his idea in 1903.) Maybe the profs were too fixated on their ingrained beliefs and their creds. That student who was more insightful than his profs was the same Arrenhius who pointed out the existence of a greenhouse effect in which small changes in the concentration of carbon dioxide in the atmosphere could considerably alter the average temperature of a planet; again, he was going where the science leads.
So, let's focus on the data and skip the credentials. Mr. Hohenberg states, "The planet is warming a little (some glaciers do show recession), but the current warming is small (much smaller than models predicted)." Not only are most glaciers receding, Arctic Ocean ice is decreasing, tundra is warming, Greenland and Antarctica are losing ice, etc. Ask those living in polar regions if the warming is small. As far as the experiment done by Earth 400 million years ago proving anything, is there any concern that maybe, just maybe there were other differences, e.g. solar-energy output, distribution of land impacting ocean currents, solar energy flux per unit area (e.g. if much land were near the poles rather than near the equator), amount of land area (above sea level), the rate of CO2 increase relative to the rate that ocean currents move heat to depths, etc, etc. That experiment proves nothing for today's situation.
The trend in increasing global temperature over the past 120 years closely matches the trend in CO2 increase, consistent with science expectations unless there is considerable growth of cloud cover, which hasn't happened. There is a considerable time lag for so many effects related to climate, and some have rather considerable positive feedback (an engineering concern if one is trying for controllability) that it is extremely risky to proceed as we've been doing, given this is the only planet on which we function.
Models of our extremely complex climate system are extremely challenging and apt to be wrong in details. That does not mean the science of Earth warming by atmospheric GHGs is wrong. And we now have higher levels of CO2 than at any time in the past 400,000 years, and are headed higher. Positive feedback, long time constants, complex system, GHGs contribute to global warming: How much risk do you want to take for your future generation? I do not want much.