The Second Law, Radiative Transfer, and Global Warming

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled Spontaneous Change and Equilibrium.

Does global warming violate the second law of thermodynamics?  Such a claim may seem strange.  The idea that the vast majority of physical scientists would subscribe to an idea that somehow violates a fundamental law of thermodynamics on its face seems odd.  Yet, such a claim is often made by people calling the science behind global warming into question.

Carbon Dioxide Poll

A recently closed poll on this blog posed the following question.  "The bending mode of carbon dioxide is:" Respondents were to respond with the best answer.  Here were the choices:

• A Hoax
• Not Dipole Allowed
• Degenerate
• A Blackbody
• The reason the sky is blue
• Even though I understand Global Warming, I don't know
• I don't know

I should point out that the answer to the question can be found in a post on this blog. The results of the poll are shown here:

What the Second Law Does Not Say

This post is part of a series, Nonsense and the Second Law of Thermodynamics.

The Second Law does not say it is impossible for heat to be transferred from a cold body to a hot body.  The second law does not say that "disorder" must increase on the earth or anywhere else.  Life is not a counter-example to the second law; life is an example of the second law in action.

One has to be very careful about applying statistical results to a single molecule or a few molecules and remembering that increasing entropy applies to irreversible changes, not reversible ones. The second law says nothing about disorder. The second law does not prevent evaporative coolers from operating.

The second law does not contradict radiative transfer theory or global warming. The second law does not contradict conservation of energy.  In applying the second law to  cosmology, one should tread cautiously.

Nonsense and the Second Law of Thermodynamics

Introduction

The Second Law of Thermodynamics is, perhaps, the most abused physical law of all time. It may be rivaled for that distinction by the Uncertainty Principle, Relativity, and Hawking Radiation, but I think the Second Law probably wins the contest.

There is a plethora of nonsense disseminated on the web and elsewhere that misrepresents what the law actually says. This series is an attempt to curb some of that nonsense.  Along the way, I hope to make some sense of what the second law of thermodynamics actually does say, as well as addressing some of the nonsense that people believe about it.

Reformatted Post on Beer's Law

I have had to reformat the post on Beer's Law.  The html editor at Blogspot seems to do strange things with <br> tags.

Radiative Transfer

If you are following this primer on infrared spectroscopy and global warming you already have some of the basics of radiative transfer.  The previous post in this series develops a simple multi-layer model of the carbon dioxide in the troposphere.  It leaves out many important features but shows conceptually how absorption and emission behave in layers of the troposphere.

The current post is intended to wrap up the topic and touch upon a few issues that were not discussed. It is possible to teach a year-long course in radiative transfer (or even multiple courses); so of course this post does not do the topic justice, but perhaps it provides some basic principles that give the reader a cursory understanding of the topic.

A Multi-Layer Model of Carbon Dioxide

I have put together a simple multi-layer model of  carbon dioxide in the troposphere.  It is based upon the same principles as the two-layer model and the three-layer model.  It accounts for the temperature and pressure profiles from the  previous post and it is part of a primer on infrared spectroscopy and global warming.  Just like those other models there are still caveats; this model is intended to be illustrative of concepts and therefore it is conceptually simple.

A Three-Layer Model

This post is part of a primer on infrared spectroscopy and global warming. The previous post introduces a two-layer model  and is a necessary prerequisite to understanding this post.  In this post I start with the following assumptions.  There is a source of infrared radiance that has emissivity of 1, i.e., it radiates as a perfect blackbody at a temperature of  288 K.  The radiance from that layer is I₀

There is a layer of air 1000 m thick with 380 ppm carbon dioxide at a temperature of 278 K.  There is another layer of air 1000 m thick with 380 ppm carbon dioxide at 268 K.  All layers are at a constant pressure of one atmosphere.

A Two-Layer Model

This post is part of a primer on infrared spectroscopy and global warming. The previous post discusses the issue of saturation in the 14-micron band of carbon dioxide in a single-layer model.   The post before that discusses Beer's Law, and is a necessary prerequisite to understanding this post.  This post starts to look beyond the single-layer model, by discussing a two-layer model, and beginning a discussion of radiative transfer.

A Note On Saturation of the Carbon Dioxide 15-micron Band

This post is part of a primer on infrared spectroscopy and global warming. The previous post discusses Beer's Law, and is a necessary prerequisite to understanding this post.  The previous post also introduced the idea of saturation of a single layer model.  This post looks more deeply at the single-layer model and the saturation of the 15-micron band of carbon dioxide.

The Beer-Lambert Law

Introduction 


This post is part of a primer on infrared spectroscopy and global warming. The previous post  looks at the features of the spectra of molecules of interest molecules and radiation and discusses how molecules give rise to infrared spectra.  This post looks at the question of how much radiation is absorbed by gas phase molecules in a laboratory setting and examines some of the differences between the laboratory gas cell and the earth's atmosphere.

A Primer on Infrared Spectroscopy and Global Warming

Introduction

This post and the posts linked to it through section headers together form a primer on infrared spectroscopy and how it relates to global warming.  The purpose of the primer is not be to convince skeptics that global warming is real, but rather to explain some of the terms and issues being discussed in climate science.  My goal is not to write a super technical explanation of infrared spectroscopy.  That's been done so many times that it is hardly worth doing again.

Rather, my intent is to write something that clearly describes infrared spectroscopy and relates it to global warming that tries to explain some fairly technical concepts in reasonably plain language.  As such there is an inevitable loss of fidelity about some of the fine points of infrared spectroscopy.  Anyone interested in such detail can follow some of the sources that I will provide.  At some point one has to compromise between accessibility and technical accuracy.  I hope that the choices made in this primer are helpful to some people trying to understand this topic.  This post is an outline of the topics addressed in the linked entries.

What is Infrared Radiation (IR)?

Figure source

This first post starts with the basics.  It discusses the electromagnetic spectrum and where infrared radiation fits into it.  It discusses waves and their measures.  It introduces the idea of electric dipole radiation.  It discusses the units of radiation wavelength, frequency. It ends by discussing photons and energy quantization.