How to Explain Climate Change to a Skeptic

Rick Santorum has recently described climate change as a hoax – a bunch of “bogus” science that tries to make nature’s normal “boom and bust” cycle into something man-made. His comments illustrate how, despite the fact that the scientific community accepts climate change as truth, and despite the fact that the science is gaining greater acceptance among the general public, you may still run into people that just don’t believe the “theory” of climate change. In my experience working for oil companies and environmental organizations alike, I have heard pretty much every argument for and against climate change. But there are a couple truths that trump them all.

First, let’s consider the word “theory”. Colloquially, theory refers to an idea or hypothesis that has not been proven. However, a scientific theory is a hypothesis that has gone through the rigors of the scientific method, and is accepted as true after a thorough examination. Unless it is specifically noted otherwise, a scientific theory is indistinguishable from scientific fact. So, the theory of climate change, in the science realm, is scientific fact.

Analogously, the theory of gravity and the theory of nuclear physics are also theories that we live with every day. They may be hard to describe to someone who is not a scientist. But, every time we walk on the ground we see the theory of gravity in action. And every time we flip on a light, we see the theory of nuclear physics – because 20% of the electricity being used by that light bulb comes from nuclear power. Unfortunately, or fortunately, depending on your view, climate change is less immediately tangible than gravity or a nuclear reaction, so it is not so clearly obvious that is true.

This is the root the climate change debate – scientific facts versus non-scientific observations. The majority of evidence presented by skeptics is anecdotal - evidence that is based on non-scientific observations or studies that may sound compelling in isolation. One example is “It is colder today than the average for this time of year; therefore global warming is not true.” Those who cite this clearly don’t understand the difference between weather and climate. You may have also heard someone say, “The climate is cyclical, and we are just on a warming trend.” Or “The eruption of Mt. Pinatubo has changed the climate more than we have.”

I am not saying that volcanic eruptions, or solar flares, or natural changes in the biosphere don’t change the climate. They do. Sometimes significantly. But that is not the argument. The argument made by skeptics is whether humans are changing the climate.

In order for the anthropogenic (human caused) climate change ‘theory’ to be true, there are two corollary truths that must also be proven. Find failings with one and you have broken the climate change theory. Prove them both, and human caused climate change must be true.

Corollary #1 - Carbon dioxide is a greenhouse gas.

The ‘theory’ that carbon dioxide is a greenhouse gas has been tested and confirmed thousands of times. But if for some reason you don’t believe it, here is an experiment that you can do at home, courtesy of NASA. You can also add a few steps to the experiment to test the effects of aerosols on temperature change. But for just CO2, consider the following:

Materials:

Two or more 2-liter clear soda bottles with the label removed.

Identical thermometers for each soda bottle

Opaque tape or modeling clay

Source of carbon dioxide (CO2) – see below*

Method:

Drill the caps of the bottles to the same diameter as your thermometer. Place the thermometers through the holes in the caps several inches. Use the modeling clay or tape to hold the thermometers in place and seal the hole. Use the seltzer bottle to fill one of the bottles with your chosen source of CO 2 (see footnote to choose CO 2 source) Place the caps with thermometers onto the tops of the bottles. Put the bottles into sunshine. Make sure they receive the same amount of sun. NOTE: a heat lamp may be substituted for the sun, but you must be very careful to place the bottles exactly the same distance from the lamp. Shade the thermometers by putting a strip of opaque tape on the outside of the bottles. The tape must be the same length on both bottles. Measure the temperature of the bottles over time. Record the temperature of each bottle every five minutes for a half hour.

This is just one way to show that CO2 acts as a blanket that traps heat. There are dozens of other ways to show that carbon dioxide is a greenhouse gas, and if you put this blanket around the earth, the earth will get warmer.

Corollary #2 - Humans are putting more CO2 in the atmosphere.

Yes, there is a finite amount of carbon in the biosphere. Humans can’t add to that, but what we can do is convert carbon from a solid or a liquid to a gas. As a gas, it goes into the atmosphere, rather than staying underground. We know that we are doing this because we dig up lots of coal and oil, materials that are mostly made up of carbon, and convert that carbon to a gas. On a large scale, this gas can be measured as it is released from power plants. We can also simply measure the CO2 concentration in the atmosphere. We have measured that the concentration of CO2 in the atmosphere has been increasing by about 2 parts per million every year for the past several decades.

Another Approach

Explaining the two corollary truths may be the less scientifically esoteric approach, but there is a way to prove it mathematically, if your audience understands calculus (If Rick Santorum happens to be your audience, I would go with the simpler explanation). I have had the pleasure of proving global warming to other scientists - geologists and petroleum engineers for example, who understand math and physics, but may not have applied that knowledge to climate theory. To do this, you simply do a thermodynamic energy balance around the earth.

Step 1: Assume the Earth has no atmosphere. Calculate the average global surface temperature.

To calculate the Earth’s average surface temperature, you can use the Stefan-Botzman Law for a blackbody.

In this equation, E is the rate of incident solar irradiance, which can be assumed to be about 238 Watts per square meter.***

Solving for temperature:

Step 2: Add in the atmosphere. Recalculate the average global surface temperature.

For this calculation, the atmosphere can be regarded as a thin layer with an absorbtivity of 0.1 for solar radiation and 0.8 for infrared radiation. Let X equal the irradiance of the earth's surface and y the irradiance (both upward and downward) of the atmosphere. E is the irradiance entering the earth-atmosphere system from space averaged over the globe (E = 238 W/ m2 from the previous equation).

At the earth's surface, a radiation balance requires that:

Solving these equations simultaneously reveals that x = 377 W/ m2 and y = 163 W/ m2.

Again, by using the Stefen-Boltzman Law, you can now calculate the temperature of the surface of the earth.

You can see that with an atmosphere, the average surface temperature of the earth is actually 13 degrees C. Taking it one additional step, you can calculate the increase in absorbtivity that would be needed to increase the global average surface temperature by 1 degree Celsius. Using the equations above, you can show that to increase the global average surface temperature by 1 degree, the absorbtivity of the atmosphere would only need to increase from 0.8 to 0.8166.

No matter how you decide to describe it – through hands on experiments and measurements, or through the calculations - climate change is happening. The sooner we all accept it, the sooner we can start working together to both reduce our emissions and adapt to the changes that are already happening.

* For your source of carbon dioxide, you may use one of the following methods:

Dry CO2 source - Seltzer bottle charges - fill a dry seltzer bottle with one charge of carbon dioxide. You will use the carbon dioxide in the seltzer bottle to fill one of the bottles with carbon dioxide. For this method, both bottles can be left dry. Wet CO2 source - Alka-seltzer - you will put a cup of water into both bottles, then put a couple of alka-seltzers into the water in one of the bottles. A tablespoon of baking powder can be substituted for the Alka-seltzer. Wet CO2 source - Put a cup of club soda or seltzer water in one of the bottles and a cup of tap water into the other bottle

** The problem presented is adapted from Wallace and Hobbs, 1977 as it was re-printed in Allen and Shonnard in their text, Green Engineering: Environmentally Conscious Design of Chemical Processes (2002).

***E is defined here as the infrared planetary irradiance, which is calculated using the incident solar irradiance (S = 1,360 W/m2), the radius of the earth (R, in meters), and the fraction of the total incident solar radiation that is reflected back into space without being absorbed (A = 30% = 0.3). An energy balance of the system produces the following equation:

About the author:

Scott McNally has a B.S. in Chemical Engineering from the University of Texas. He has worked as an Environmental Engineer for Valero Energy Corporation, a Project Engineer for Shell Oil Company, and an energy and climate research intern for the White House Council on Environmental Quality. Scott is a frequent guest blogger at Plugged In – he was invited to be a guest blogger by Plugged In’s Melissa C. Lott. You can reach Scott via e-mail at scottmcnally at gmail dot com.