Challenges to the CO2 Global Warming Hypothesis: (3) The Greenhouse Effect Doesn’t Exist
By Physicist Ralph B. Alexander
This final post of the present series reviews two papers that challenge the CO2 global warming hypothesis by purporting to show that there is no greenhouse effect, a heretical claim that even global warming skeptics such as me find hard to accept. According to the authors of the two papers, greenhouses gases in the earth’s atmosphere have played no role in heating the earth, either before or after human emissions of such gases began.
The first paper, published in 2017, utilizes the mathematical tool of dimensional analysis to identify which climatic forcings govern the mean surface temperature of the rocky planets and moons in the solar system that have atmospheres: Venus, Earth, Mars, our Moon, Europa (a moon of Jupiter), Titan (a moon of Saturn) and Triton (a moon of Neptune). A forcing is a disturbance that alters climate, producing heating or cooling in this case.
The paper’s authors, U.S. research scientists Ned Nikolov and Karl Zeller, claim that planetary temperature is controlled by only two forcing variables. These are the total solar irradiance, or total energy from the sun incident on the atmosphere, and the total atmospheric pressure at the planet’s (or moon’s) surface.
In addition to solar irradiance and atmospheric pressure, other forcings considered by Nikolov and Zeller include the near-surface partial pressure and density of greenhouse gases, as well as the mean planetary surface temperature without any greenhouse effect. In their model, the radiative effects integral to the greenhouse effect are replaced by a previously unknown thermodynamic relationship between air temperature, solar heating and atmospheric pressure, analogous to compression heating of the atmosphere. Their findings are illustrated in the figure below, in which Ts is the surface temperature and Tna the temperature with no atmosphere.
A surprising result of their study is that the earth’s natural greenhouse effect – from the greenhouse gases already present in Earth’s preindustrial atmosphere, without any extra CO2 – warms the planet by a staggering 90 degrees Celsius. This is far in excess of the textbook value of 33 degrees Celsius, or the 18 degrees Celsius calculated by Denis Rancourt and discussed in my previous post. The 90 degrees Celsius result, however, is the same as that derived in a 2014 paper on the natural greenhouse effect, using an analytic model unrelated to the dimensional analysis of Nikolov and Zeller.
Needless to say, Nikolov and Zeller’s work has been heavily criticized by climate change alarmists and skeptics alike. Skeptical climate scientist Roy Spencer, who has a PhD in meteorology, argues that compression of the atmosphere can’t explain greenhouse heating, because Earth’s average surface temperature is determined not by air pressure, but by the rates at which energy is gained or lost by the surface.
Spencer argues that, if atmospheric pressure causes the lower troposphere (the lowest layer of the atmosphere) to be warmer than the upper troposphere, then the same should be true of the stratosphere, where the pressure at the bottom of the stratosphere is about 100 times larger than that at the top. Yet the bottom of the stratosphere is cooler than the top.
In a reply, Nikolov and Zeller fail to address Spencer’s stratosphere argument, but attempt to defend their work by claiming incorrectly that Spencer ignores the role of adiabatic processes and focuses instead on diabatic radiative processes. Adiabatic processes alter the temperature of a gaseous system without any exchange of heat energy with its surroundings.
The second paper rejecting the greenhouse effect was published in 2009 by German physicists Gerhard Gerlich and Ralf Tscheuschner. They claim that the radiative mechanisms of the greenhouse effect – the absorption of solar shortwave radiation and emission of longwave radiation, which together trap enough of the sun’s heat to make the earth habitable – are fictitious and violate the Second Law of Thermodynamics.
The Second Law forbids the flow of heat energy from a cold region (the atmosphere) to a warmer one (the earth’s surface) without supplying additional energy in the form of external work. However, as other authors point out, the Second Law is not contravened by the greenhouse effect because external energy is provided by downward solar shortwave radiation, which passes through the atmosphere without being absorbed. The greenhouse effect arises from downward emission from the atmosphere of radiation previously emitted upward from the earth.
Furthermore, there’s a net upward transfer of heat energy from the warmer surface to the colder atmosphere when all energy flows are taken into account, including non-radiative convection and latent heat transfer associated with water vapor. Gerlich and Tscheuschner mistakenly insist that heat and energy are separate quantities.
Both of these farfetched claims that the greenhouse effect doesn’t exist therefore stem from misunderstandings about energy.