We’ve used the last couple posts to discuss a few common myths dismissing climate change: why cold days during winter do not disprove that the Earth is getting warmer and why a few days of temperatures outside the norm isn’t necessarily indicative of changes in the climate. In this article, we will tackle perhaps the most pervasive and important climate change myth of all: that carbon dioxide is not causing the Earth’s temperature to rise.
Despite what many industry groups, American politicians, and the current director of the Environmental Protection Agency say, there is actually very little disagreement on the cause of the increase in global temperatures. In fact, there may be more disagreement among the scientific community on the theory of gravity than there is about carbon dioxide (CO2) emissions warming the earth. Though outliers always exist, nearly all climatologists, ecologists, biologists, zoologists, and botanists agree with 95% confidence: carbon dioxide, released from decades of burning fossil fuels, is having a, clear, measurable, and statistically significant effect on the increase in global temperatures.
Correlation vs. Causation
Before we start looking at data, we need understand a couple important statistical terms. Correlation is when two random variables have a mathematical relationship. For example, the number of films Nicolas Cage makes in a year correlates almost perfectly with the number of people who have died by falling into a pool and drowning. However, that doesn’t mean your chances of drowning increase just because Nicolas Cage is in a lot of movies that year. While the two variables match, they do not affect one another.
Causation is when two variables have a direct relationship, a change in one will cause a change in the other. Scientists need to be able to show evidence of the data not only matching up but affecting one another. An easy example of this is brushing your teeth and cavities; you are more likely to get cavities the less you brush your teeth. Changing the frequency of which you brush your teeth will lead to a change the number of cavities. More importantly, we also have a scientific mechanism for this to work. Not brushing leads to more bacteria growing on your teeth, which eat away at the enamel, and forms cavities. This leads us to our greatest challenge in showing that carbon dioxide is the main contributor to global warming; we need to clearly show a mechanism and evidence for a causal relationship.
What does the data tell us?
Global temperatures have only been recorded since about 1850 and direct observation of carbon dioxide levels in the atmosphere have only been taken since 1950. We’ll discuss later on about the techniques used collect carbon data before that, but for now, let’s focus on what we can observe directly.
If we look at both variables side by side, we can see that there is a clear match between levels of carbon dioxide in the atmosphere and global temperatures. Even if we only look at when direct observation started in the 1950’s, it’s pretty obvious that there is a correlation between the two variables. But is this a causal relationship? In order for us to see if an increase in carbon dioxide has caused global temperatures to rise, we need to show how causal relationship works.
Carbon dioxide: little molecule, big job
Carbon dioxide (CO2) is a naturally occurring gas in the Earth’s atmosphere, containing 1 carbon atom and 2 oxygen atoms covalently bonded (they share electrons). While CO2 only makes up about 0.04% of our atmosphere (the rest is made of around 78% nitrogen (N2), 20.95% Oxygen (O2), and some other trace compounds), that little bit has a very big job: keeping our planet warm.
When the Sun gives off thermal radiation (heat), most of that energy is emitted as infrared waves. Carbon dioxide is very good at absorbing this type of radiation, the molecule’s linear shape and electron distribution allows it to wiggle and vibrate when absorbing photons of this wavelength, causing the molecule to take on energy (you can learn more about this here). This is what scientists call The Greenhouse Effect, and it traps the heat given off by the Sun in our atmosphere, allowing for our planet to stay warm. Click on the links to learn more about electromagnetic radiation and absorption spectra.
Without carbon dioxide in our atmosphere, the heat that we receive from the Sun would float off into space, leaving the Earth around 0° F (-18°C), much colder than it is now. The atmosphere also helps distribute the heat energy absorbed close to the equator, keeping areas of higher latitude and the side of the Earth not facing the Sun warm.
Too much of a good thing
Carbon dioxide is also the product of a unique chemical reaction called combustion. Combustion is the reaction of a hydrocarbon with oxygen gas, producing carbon dioxide and water. These hydrocarbons are molecules made of, you guessed it, hydrogen and carbon bonded together. Common examples include methane (CH4 – natural gas), octane (C8H18 – found in gasoline), and propane (C3H8 – used in gas grills). This reaction produces a lot of energy, which can be used to power things like your car, your stove, or electric generators.
Since the beginning of the industrial age, the combustion reaction has used hydrocarbons to power factories, power plants, and a host of life-changing technology. This transformation brought generations of humans out of poverty, helped usher in the age of antibiotics, and expanded lifespans and life quality for billions of people around the globe. However, it also had another unexpected consequence. The carbon dioxide released from those reactions went into the atmosphere. After two centuries of industrialization, humans are currently pumping 40 billion tons of carbon dioxide into the atmosphere per year, significantly altering its composition, and as a result, the atmosphere’s ability to absorb heat.
A historical precedent
But is there any evidence of carbon dioxide levels in the atmosphere affecting global temperatures? Scientists have found samples of ancient atmospheres by drilling ice cores from Antarctic glaciers. When the glaciers were formed, they trapped tiny bubbles of air in the ice, preserving them over time. Researchers are able to analyze these air bubbles to find out the composition of the atmosphere over the last 650,000 years and compare it other data from the geologic record. What has been seen is that lower levels of carbon dioxide match up with ice ages, evidence that carbon dioxide, in addition to patterns in the Earth’s orbit called Milankovitch cycles, helps drive global temperatures.
What is unprecedented in the last few hundred years of human activity is not just how much the levels have increased, but the rate by which it has increased. Though the Earth does indeed go through cycles of warming and cooling, these cycles can take nearly one hundred thousand years to go through. We have seen an unprecedented increase of atmospheric carbon dioxide in less time than human life span, three orders of magnitude less than a natural cycle. Clearly, something is causing a considerable rise in the amount of atmospheric carbon dioxide that is well outside natural patterns.
How significant are these changes?
It’s hard to understate how abnormal this is. The significance and rate of the changes we are currently observing in our atmosphere have never been seen in the geologic record. The vast majority of species cannot adapt to changes that quickly. It’s why we have seen so many habitats and ecosystems suffer devastating population losses. But just as significantly, humans are facing challenges coping as well. Droughts, wildfires, severe weather, and water shortages have all made headlines are likely to get worse as the century progresses and global temperatures continue to increase.
And while some will point out that carbon dioxide is used by plants for photosynthesis, that ignores that massive deforestation that has occurred over the last 40 years. The Amazon Rainforest alone has lost 17% of its forests to cattle ranching. This exacerbates the problem, as the carbon dioxide in the atmosphere ends up staying there without plants to absorb it. We’ve put so much carbon dioxide into the atmosphere, in order to offset the world’s carbon usage, we would have to plant a forest an area about the size of Spain, 500,000 square kilometers or 50 million hectares, PER YEAR. Then maintain that forest in perpetuity.
A causal relationship
The data is pretty clear: atmospheric carbon dioxide levels and global temperatures have been increasing for the last several decades, starting when fossil fuels were needed to power large scale industrialization. The correlation is obvious. What is less obvious is the causal relationship: the increase in carbon dioxide levels causes an increase in average temperatures around the globe. Its unique ability as a molecule to absorb thermal radiation provides us a mechanism for it trapping heat from the Sun here on Earth. While this property is vital in making sure our planet stays warm enough for water to remain in liquid form, the recent increase in carbon dioxide levels has risen at rates never before seen.
Our civilization’s commitment to burning fossil fuels to power our modern society has reached a point where we have altered the composition of the atmosphere, allowing for more thermal energy from the Sun to be trapped, causing temperatures across the world to rise. The corroboration in the between carbon dioxide’s unique molecular properties, the geologic record showing carbon dioxide levels corresponding to warming and cooling periods, and the unheard-of rate of increase in atmospheric carbon dioxide from the burning of fossil fuels gives us strong evidence that, indeed, human activity is causing the Earth to heat up.
As a society, this is hard to hear, something which is an integral part of life in the industrialized world is harming the planet. It’s easy to see why people would either choose not care or deny it outright. Even without the influence of special interests, it’s extremely hard to change such a pervasive aspect of our civilization. But the purpose of science is not about proving your opponents wrong or pushing an agenda. Scrutiny is not a bad thing, it leads to higher confidence in conclusions. Science, in it’s truest form, is to pursue a greater understanding of the world around us. While disagreements may come from how the climate will change and to what extent those changes will take place, the vast majority of scientists agree, that the burning of fossil fuels has led to an increase in carbon dioxide levels in the atmosphere, which is without a doubt, warming the Earth.
Learn and do more
Check out Skeptical Science, an excellent blog debunking climate change myths, contributed to by climate scientists all over the world, updated daily
Calculate the amount of carbon dioxide that you put into the atmosphere and find out ways that you can reduce your carbon footprint: http://www.carbonify.com/carbon-calculator.htm
Learn more about correlation vs. causation and why some nutrition studies can’t be trusted: http://fivethirtyeight.com/features/you-cant-trust-what-you-read-about-nutrition/?ex_cid=538twitter
Donate to trees for the future and help impoverished families across the world build a sustainable income while rebuilding the carbon reservoir: http://trees.org/
Read a more detailed explanation of the greenhouse effect: http://www.windows2universe.org/earth/climate/greenhouse_effect_gases.html