By Ron Barmby

I’ve looked at climate change from both sides now, and I have found common ground between proponents and skeptics of the belief that climate change is largely caused by humans. When it comes to forecasting global temperatures, distinguished experts in both camps agree a dominant variable cannot be simulated in computer models because clouds get in the way.

Among the proponents is Dr. Bjorn Stevens, a contributing author to the Intergovernmental Panel on Climate Change (IPCC) Assessment Report 5 (2014). Dr. Stevens is also director at the Max Planck Institute for Meteorology, Hamburg, Germany, and a cloud expert. In a recent interview he acknowledged the contribution of clouds to global warming is overestimated in the IPCC’s “Climate Change 2021: The Physical Science Basis.”

“Clouds are tricksters,” he said, referring to their complexity. However, he said, many scientists use oversimplified representations of clouds in modeling “as a guide because they are easier to simulate. This makes the climate models less accurate.”

On the skeptic side is Dr. Richard S. Lindzen, a former lead author for IPCC Assessment Report 3 and now a vocal critic of the IPCC. In a recent podcast the interviewer noted that Lindzen had published sufficient research papers to earn 80 PhDs. (Lindzen humbly declined the praise.)

Lindzen, professor emeritus of Atmospheric Sciences at the Massachusetts Institute of Technology,  points out that IPCC models rely on the assumption that water vapor and clouds amplify the greenhouse gas effects of CO₂ in order to achieve forecasts of catastrophic global warming. The IPCC theory is that a warmer atmosphere will have a higher content of water vapor – itself is a greenhouse gas – that adds to the warming caused by CO₂. Without this amplifying “positive feedback” effect, the models are still wrong for many reasons, but they no longer project “catastrophic” warming.

Dr. Stevens, who is on record stating that global warming is a “huge problem,” agrees that increased clouds do not amplify global warming: “Water-rich low clouds over the tropical ocean have the greatest cooling effect and low-water ice clouds at high altitudes have the strongest warming effect. Overall, the cooling effect is greater.” That’s called “negative feedback.”

Dr. Lindzen argues that global average temperature is controlled by the polar regions. The temperature at the tropics remains relatively constant over long periods of time while the polar regions have significant variations. In other words, a small change in global average temperature is the result of a big change in polar temperatures. The stability of tropical temperatures indicates that increased clouds provide negative feedback in times of global warming. Rather than exacerbating the global warming effect of CO₂, clouds reduce it.

Lindzen proposes the mechanism by which greater negative feedback is produced: High altitude cirrus clouds (Dr. Stevens’ low-water high altitude ice clouds that cause warming) control heat emissions to space. As the air below these clouds warms, the cirrus clouds dissipate and allow more energy to radiate into space. He calls this the Iris Effect.

Nature is dominated by negative feedbacks, not positive ones. French chemist Henry Louis Le Chatelier expresses this in Le Chatelier’s principle: A system in dynamic equilibrium (in this case the climate) is disturbed by changing the conditions (in this case the concentration of CO₂), then the equilibrium moves to counteract the change. Negative feedbacks occur because when a variable changes, other variables react in ways that offset the shift.

We can’t model clouds. The IPCC admits this. Nonetheless, its forecasting models rely on assumptions that clouds amplify CO₂ warming, without which its temperature forecasts are benign (that’s strike one).

IPCC forecasts based on cloud models have been called out by eminent cloud experts on both sides—proponents and skeptics of the notion of human-caused climate change. A recognized cloud expert and IPCC author (Dr. Stevens) states that clouds cause cooling overall, not warming (strike two).

And, finally, the observed stability of tropical temperatures argues that increased clouds provide even greater negative feedback to CO_2, and a cloud expert who has done enough research for 80 Ph.D.s (Dr. Lindzen) has an idea how that happens (strike three).

Clouds do not amplify global warming; they promote global cooling. That’s enough to convince this climate heretic that IPCC forecasts are no “red light” for humanity and to reject the insane drive to eliminate CO₂ from our economies.

IPCC forecasters overstate warming because they still somehow really don’t understand clouds at all.

This commentary was first published at Real Clear Markets, April 7, 2023, and can be accessed here.

Ron Barmby, Professional Engineer with a master’s degree majoring in geosciences, had a 40-year career in the energy industry that covered 40 countries and five continents. He is author of “Sunlight on Climate Change: A Heretic’s Guide to Global Climate Hysteria” and is a proud member of the CO₂ Coalition, Arlington, Virginia.