How To Win an Argument with a Climate Skeptic

Climate science is an extremely complicated discipline. Climate change skeptics and deniers, I believe, thrive on this complexity. They highlight what is not known or not agreed upon to suggest that the discipline as a whole is flawed. The best way to combat such an argument is with simplicity.

In that light, I present a simple, four-point argument demonstrating the reality of anthropogenic global warming.

Carbon Dioxide Causes Warming

The central mechanism driving anthropogenic climate change is the combustion of fossil fuels. Fossil fuels, the chemicals we use to heat our houses and move our cars, are compounds formed when ancient organic material, predominantly the remains of algae, is buried and cooked at a high temperature and pressure for millions of years. The result is a set of carbon-based chemicals that release a lot of energy, and form carbon dioxide (CO2), when burned.

Svante Arrhenius

This CO2, when released into the atmosphere, traps heat by blocking the escape of Earth’s radiation into space. (Anything that has a temperature, Earth included, produces radiation.) Known as the greenhouse effect, this is not a new or controversial idea. In 1861, John Tyndall, a British professor of natural philosophy, gave a lecture titled “On the Absorption and Radiation of Heat by Gases and Vapours, and on the Physical Connexion of Radiation Absorption and Conduction.” Tyndall demonstrated conclusively that CO2, among other gasses, absorbs long wave radiation – the same type that Earth emits to space.  His experiment was simple. Tyndall produced radiation with a bunson burner, knowing that the heat would emit a full spectrum of wavelengths, including long-wave radiation. He then measured those wavelengths after passing them through different gasses. Because not all wavelengths traveled through the CO2, Tyndall concluded that the CO2 must be absorbing some of the heat. This simple experiment has huge implications for our planet.

John Tyndall

Tyndall’s work greatly influenced a Swedish physicist named Svante Arrhenius. In 1896, Arrhenius published a paper titled “On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground.” (Carbonic acid was what carbon dioxide was called at the time.) Arrhenius, in essence, took Tyndall’s work out of the lab and applied the concept to the real world. Instead of a bunson burner, he used observations of infrared radiation from the moon. Because he knew that the moon, without an atmosphere, should transmit all of its long wave radiation to Earth, he was able to calculate the effect our atmosphere had on it by documenting which wavelengths didn’t make it. For each lunar observation, he compared that data with atmospheric conditions (humidity and CO2 levels) to see what effect they had on the radiation that made it to Earth. By doing this he determined that with a rise in CO2 came a “nearly arithmetic” rise in temperature. Using his calculations he determined that a doubling of atmospheric CO2would result in a 5ºC temperature rise. Even with the advent of massive computer models and high-tech lab equipment, this value is still in agreement with modern climate science.

Both Tyndall and Arrhenius speculated that CO2 has played a role in controlling the Ice Ages.  Arrhenius, back in 1896, even predicted that human fossil fuel use might result in future global warming.

Carbon Dioxide Concentrations in the Atmosphere are Increasing

This is the easiest point to make. Scientists can measure the amount of CO2 in the atmosphere. It is increasing.

The best evidence is the famous “Keeling Curve.” In 1958, Charles Keeling, a professor of oceanography at Caltech, began making continuous measurements of CO2 on the peak of the big Island of Hawaii. Because this station is far away from major urban centers, and because the station is at a high altitude, the location is perfect for making CO2 measurements that are representative of the whole atmosphere.  His measurements, which continue to this day, show a progressive rise in CO2from around 315 parts per million in 1958 to about 394 ppm as of September 2012.

The Keeling Curve

The Increased Carbon Dioxide is Coming from Human Activity

This is the heart of the controversy, but this is just as easy to demonstrate as the previous two points. The CO2 that is associated with the recent increase has a chemical signature that unequivocally ties it to human activity.

CO2 can come from a variety of sources. CO2 in the ocean is constantly exchanged with CO2 in the atmosphere; there is CO2 in the mantle, which can be released through volcanoes, and wildfires can release CO2 the same way that burning fossil fuels does. By looking at the carbon contained in CO2, scientist can distinguish between each of these sources.

Fossil fuels come from the cooked remains of ancient life. Therefore, the carbon in this CO2 must be derived from the remains of living things that existed a very long time ago. Both the age and the source of carbon can be inferred using chemical entities known as isotopes.

Elements like carbon can have differing masses, caused by changes in the number of neutrons in the atom. These are called isotopes, and each isotope acts a bit differently. When a plant takes in CO2 from the atmosphere through photosynthesis, it prefers carbon with a mass of 12 to carbon with a mass of 13. Therefore, anything that photosynthesizes, or anything that eats something produced by photosynthesis (essentially all life on this planet), is composed of less carbon-13 than is typically found in the atmosphere. This is the signature of carbon that comes from living things. Life, both alive and transformed into fossil fuels, represents a massive reservoir of carbon-12. If this kind of carbon were released into the atmosphere, the concentration of carbon-13 in the atmosphere would be reduced by dilution with carbon-12.

An oil refinery in Scotland

Carbon can also have an isotope with a mass of 14. This type of carbon is created in the atmosphere continuously. Because of this, there is a constant source of carbon-14 on the surface of Earth. Unlike carbon-13, carbon-14 is radioactive. This means that it cannot remain carbon-14 forever. It slowly decays away at a known rate. This property allows scientists to use carbon-14 to date once living things, but anything past approximately 60,000 years, cannot be dated since it will have virtually no carbon-14 left. A complete lack of carbon-14 is the signature ancient carbon. If enough of it is released to the atmosphere, it will decrease the relative concentration of carbon-14 in the atmosphere by diluting it with carbon-14 free CO2.

The combustion of fossil fuels, then, should reduce the concentration of both carbon-13 and carbon-14 in the atmosphere.

Both are happening. They are known collectively as the Suess effect.  The concentration of carbon-14 and carbon-13 in the atmosphere is declining, and it is declining at the same time that CO2 is increasing. This means that the CO2 increase we are seeing must come from ancient, organic carbon.

No other source of CO2 could have this signature. Wildfires can’t because the carbon being burned is young; it has plenty of carbon-14. Carbon from the ocean has the same problem – too young, too much carbon-14. CO2 from volcanoes does not work either. This carbon does not come from once living matter, so it has plenty of carbon-13.

Carbon derived from the remains of ancient life buried deep inside our Earth is the only plausible source. The only way to release a great deal of it at once is to dig it up and burn it, as humans are doing today.

Average Global Temperatures Are Rising

Just like CO2 concentrations, scientists are able to measure air temperature – in fact the technology has been around for quite a while. The real challenge is getting past the variability, which is the result of things like el Nino and other short term weather patterns, to figure out what the long-term temperature trend is globally. There are plenty of studies showing that the trend is overall warming, but I will highlight a study by Richard Muller.

Richard Muller was an outspoken climate change skeptic, and the Koch brothers, prominent right-wing political figures who deny climate change, funded his research. He gathered as much data as possible and corrected for all known biases – the fact that temperatures are generally higher in cities, for example – and plotted average temperature since 1750. They are rising – a full degree since 1900. A degree may not sound like much, but a rise of 2 degrees would result in ~3 meters of sea level rise, according to a collection of recent estimates. Most of New York City would be underwater.

Richard Muller’s study of global temperature change. This shows annual temperatures from 1750 to the present. (www.berkeleyearth.org)

Carbon dioxide in the atmosphere can warm our planet. This has been taken as fact for well over a century – well before any widespread scientific conspiracy would have been hatched. Carbon dioxide is increasing  – it’s real hard to argue with measurements.  The increase in carbon dioxide is changing the chemical composition in the atmosphere in a way only fossil fuels are able to. Also, the planet is warming.

Pretty straightforward.

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3 Comments on “How To Win an Argument with a Climate Skeptic”

  1. Denise says:

    Great post! I don’t need convincing about climate change, but I’m glad that you have laid out the facts in such a clear 1-2-3 way. I linked to this post in my latest blog post (about sandhill cranes and how their migrations are being possibly being affected by climate change) I was glad to be able to direct any skeptics to your article. Thanks!


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