Worried about climate change? Alternately, sick to death of prophets predicting apocalypse? Take an old chemist’s advice and start your personal evaluation of the “climate crisis” by dismissing this popular trope: Earth’s atmosphere acts like an insulating blanket.
Many people worried about climate change frequently use the analogy or ones much like it. It brings home a message in a simple way that most people can understand. The idea is that too much greenhouse gas in the atmosphere acts kind of like a treble-thick lambs’ wool comforter, trapping heat that would otherwise escape into empty space.
Although that overly simplistic metaphor contains little in the way of scientific fact, it has been used by those on either side of the climate change debate. Fossil fuel opponents such as Bill Nye have attempted to “demonstrate” that carbon dioxide is capable of retaining significantly more heat within Earth’s ecosystem than other gases. On the other extreme, some climate change skeptics have dismissed the entire idea that the gas composition of the atmosphere can influence global climate trends.
Both arguments are faulty, ironically for the same reason. Neither takes into account a very fundamental concept of thermodynamics: heat capacity. Thermodynamics is that part of scientific study that examines how energy moves through natural and man-made systems. Scientists interested in thermodynamics follow energy using a variety of parameters, such as temperature, pressure, volume, mass, and so forth.
Heat capacity is an important thermodynamic property to consider when we discuss the importance of atmospheric gases. Heat capacity relates to the ability of a given mass of a substance to retain energy over time, energy being most conveniently measured by the temperature of the substance.
As a rule of thumb, most solids and liquids have very high heat capacities when compared to gases, which have pretty trivial heat capacities. For example, a cubic meter of water will retain about 5,000 times more energy than a cubic meter of air. The fact that air does a poor job of retaining heat is why it gets colder at night.
But the climate change proposition isn’t about the atmosphere retaining heat, it’s about carbon dioxide reflecting heat. This is a subtle, but vitally important, difference. To understand it, we must start with how energy generated by the sun manifests itself.
Our sun produces energy at a wide variety of wavelengths, from X-rays to radio waves and everything in between. The only part of the spectrum the sun doesn’t play in is gamma rays, which is a good thing for life on Earth. Some wavelengths are reflected or absorbed or dissipated before they can reach us. Mechanisms such as the Van Allen belts and stratospheric ozone protect us from the most dangerous. Some of the energy is absorbed in the oceans and land, which are far more important heat sinks than the atmosphere surrounding them.
How does carbon dioxide affect the balance? There’s sunlight in a portion of the infrared spectrum that ordinarily bounces off the planet and is reflected back into space. Carbon dioxide can take a portion of this portion and return that energy back to Earth.
During the reflection process, the wavelength of the light shifts to a portion of infrared that the Earth will absorb, thus contributing more energy to the heat sinks that matter: land and ocean. And that’s what, in theory, heats up the planet. Not an atmosphere that acts like a blanket, but an atmosphere that slightly increases the energy deposited on the planet, such that as those heat sinks release their accumulated energy stores, they do so at a slightly higher rate. And it’s that phenomenon that ultimately manifests itself as rising atmospheric temperatures.
Admittedly, this is an oversimplification of an enormously complex system, but it’s a better approximation of reality than the blanket analogy. The fact is that the Earth’s climate is an enormously complex system with hundreds if not thousands of inputs and outputs involved. To my knowledge, no legitimate climatologist, even the most ardent skeptic, has denied that concentrations of carbon dioxide can have some effect on climate. The question really is how significant that effect is compared to all the other factors involved.
Noted skeptical climatologist Roy Spencer said it best when he observed, “If the climate is as sensitive to small changes in carbon dioxide concentrations as some of my colleagues seem to think, then there’s really nothing we can do about it anyway.”
In the unlikely event that you should find yourself engaged in a civilized conversation with someone who still retains an open mind about climate change, this point is definitely worth mentioning.
