This letter is in response to the letter from Graham Turk ’17 and his criticism of Professor William Happer *64. 

Contrary to Mr. Turk’s opinion, Professor Happer is eminently qualified to comment on climate change, its causes, and its effects.  As the Cyrus Fogg Brackett Professor (Emeritus) of Physics at Princeton; JASON Advisory group; trustee of the Mitre Corp., the Richard Lounsbery Foundation, and the Marshall Institute; chairman and founder of Magnetic Imaging Technologies, where he pioneered the adaptive optics (critically needed for Earth-based astronomy); and presidential adviser, Professor Happer is a critical thinker, a real scientist who follows no one but takes the paths where true science leads. The Earth’s climate is a complex system that is not easy to model, but luckily science does not rely on models without observation and test.  Professor Happer would join me in some of the following observations:

(1) Man has certainly increased atmospheric CO2, but we have no choice except to burn fossil fuels, since we need the energy and there is no alternative right now.

(2) The planet is warming a little (some glaciers do show recession), but the current warming is small (much smaller than most models predicted).

(3) Our CO2 increases cannot cause runaway global heating (as shown below), so we are not on the verge of catastrophe. And contrary to popular belief, the extra CO2 is actually good for plants, not the other way around.  Plants are carbonaceous, and the only source of carbon for them is atmospheric CO2, a necessary plant food. At CO2 levels below about 160 ppm, photosynthesis will not occur and no plants will grow. The atmosphere was very short of CO2 before the Industrial Revolution at 320 ppm (now we are at 400 ppm), fairly close to the critical 160 ppm level for plant growth. Experiments show maximum growth rates occur at CO2 many times our present levels, so although man has certainly increased the CO2 level somewhat in our atmosphere, don’t look a gift horse in the mouth: Plant growth has substantially accelerated (, and many others).

(4) The Vostok ice cores show that global temperature and atmospheric CO2 content do correlate, but it is the temperature that drives the CO2, not the other way around, as shown by the fact that these cores preserve the time record and temperature changes precede CO2 changes by several thousand years. The effect cannot precede the cause.

Water vapor is the dominant greenhouse gas for our planet, and it is water vapor that warms us about 60 degrees F to a more livable and comfortable climate (a certain location that has a 50 degrees F average temperature would average -20 degrees F without our water-vapor blanket). CO2 is also a greenhouse gas, but it is not nearly as important as water vapor, since its IR absorption bands are much stronger and H2O concentration in the atmosphere is about 100 times that of CO2. However, things are not that simple. CO2 is always a gas while water vapor condenses as clouds, freezes out as ice, and evaporates into the atmosphere depending on a wide variety of conditions. 

So the operation of our greenhouse system, and the planetary climate it impacts, is very complex. It has not been successfully modeled as shown by the multitude of failed models comparing predictions with actual measurements that are now emerging. To show the complexity of our climate, look no further than El Niño and La Niña, subtle changes in the oceans that greatly affect our climate. There are no models that predict their impact, and this simply demonstrates the complexity of our climate and how difficult it is to model.

How does a scientist address a system too complex to model, or test a model that he has constructed? He does the critical experiments to see what happens (truth is always better than theory!). How do we do such an experiment, one that addresses the impact of increased CO2 in the atmosphere, by direct experiment? We are lucky. Our planet has already done the experiment for us, and we can use those results to evaluate the potential effects of manmade CO2 in the atmosphere: 400 million years ago the CO2 content of our atmosphere was 50 to 100 times higher than it is now but the planet was only slightly warmer, so we do not need to worry about a runaway greenhouse effect due to modest increases in atmospheric CO2 from fossil fuels. Moreover, at that time the planet resembled a tropical rain forest, so it was more like the garden of Eden than a wasteland. The vegetation, growing quite well, produced the fossil fuels we see and use today – the coal, the natural gas, and the oil under what is now Saudi Arabia, which was then lush and green but now a desert.

So the experiment has been done and the results are in: No runaway heating, and plants grow better with increased CO2. It would serve us all better to observe the results of real scientific experience (the historical Earth) and respect the views of real scientists like William Happer, not those who promote an unsupported point of view.

Charles M. Hohenberg ’62, Professor of Physics (Emeritus), Washington University
St. Louis, Mo.