SkS Analogy 6 - Speakers, tuning forks, and global warming

Tag Line

The physics of global warming by greenhouse gases is well understood and can be illustrated by items we use every day.

Elevator Statement

Simple, well-understood physics indicate the following:

• Sound waves vibrate speakers (think microphone¹) and vibrating speakers make sound waves
• Sound waves vibrate tuning forks and vibrating tuning forks make sound waves (with a narrow range of frequencies)
• Infrared waves vibrate CO₂ molecules (increased vibration means more energy, which means warmer) and vibrating CO₂ molecules make infrared waves (think CO₂ lasers, which make waves with a narrow range of frequencies)

Almost everybody is familiar with microphones, speakers, and tuning forks. These are items you can see, touch, and feel, so they are familiar. Even though we cannot see greenhouse gases like CO₂, they operate the same as speakers and tuning forks: they absorb and reemit waves, just on a very small scale. When they absorb waves they trap heat, warming the atmosphere.

Excitation of tuning fork by sound and CO₂ molecule by infrared radiation.

Climate Science

The physics of how CO₂ molecules interact with infrared waves was first discovered in the 1850’s. Einstein had not even been born by the time that we knew that CO₂ combined with infrared radiation caused warming in the atmosphere. By the 1890’s the first calculation was made of how much the atmosphere would warm up if we doubled CO₂ concentrations (i.e., equilibrium climate sensitivity, ECS). This work was published by Svante Arrhenius, a Nobel prize winner, and was titled “On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground” (read here). Since Arrhenius’ original calculations, estimates of the climate sensitivity have been refined, and the current average estimate from the IPCC is about 3°C of warming for doubling CO₂.

Study of the interaction between infrared radiation and atmospheric gases was significantly ramped up in the 1950’s when the US Air Force developed heat-seeking missiles. The Air Force wanted their sensors to “see” the hot exhaust of airplane engines, and so they had to learn which wavelengths were least affected by atmospheric gases such as CO₂. The physics of how CO₂ molecules and infrared radiation interact has also been used to develop CO₂ lasers. Therefore, from many types of research, we have learned about the detailed interactions between infrared radiation and atmospheric gases. This is well-understood science.

For a more in-depth look, see the "The History of Climate Science" by John Mason.

By now the physics that tells us that increasing atmospheric CO₂ levels increases atmospheric warming is well understood by all major academies of science, the Vatican, the insurance industry (they see the rising financial losses from increasing weather-related disasters), the US military (they refer to Climate Change as a threat multiplier), and many others. More than 97% of climate scientists agree that increasing greenhouse gas concentrations in the atmosphere are causing the Earth to warm up. What does it say when an organization like the United Nations, which acts cautiously by consensus of most of the world’s leaders, states the following regarding the link between CO₂ and global warming (read herel)?

“There are some basic well-established scientific links:

• The concentration of GHGs in the earth’s atmosphere is directly linked to the average global temperature on Earth;
• The concentration has been rising steadily, and mean global temperatures along with it, since the time of the Industrial Revolution;
• The most abundant GHG, carbon dioxide (CO₂), is the product of burning fossil fuels.”

Put more CO₂ into the atmosphere, and there are more CO₂ molecules absorbing infrared radiation. CO₂ molecules share their energy with the surrounding air molecules, the atmosphere heats up, and so do we.

It is basic physics. The same physics known for over 150 years and illustrated by a common, musical, tuning fork.

1. A microphone is really just a small speaker used in reverse.

For a more in-depth look at the detailed physics that governs the interaction between GHGs, infrared radiation, and ultimate heating, see the following SkS articles.

Is the CO2 effect saturated?

Rob Honeycutt's chapter on "Radiative Gases".

Posted by Evan on Monday, 29 May, 2017

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