There are few topics with a wider disconnect between what scientists know to be true and what the general public thinks than global warming. Based on the most recent Gallup poll numbers (which were from 2013 when this post was written), only 54% of Americans think that climate change is already happening, 39% think that its natural rather than anthropogenic, and only 62% think that there is a scientific consensus about it. In reality, roughly 97% of climatologists agree that the planet is currently warming and we are causing it. This disparity is largely attributable to a great deal of misinformation about climate change. The internet is full of nauseatingly horrible arguments like, “well it changed naturally in the past, so it must be natural now” or the erroneous claim that “in the 70s all the scientists were predicting global cooling” and the misconception that “climate change has paused during the past 15 years.” Therefore, I am going to try to briefly explain how climate change actually works, and present a logical proof that we are causing it. According to the rules of logic, the inane dribble of the internet will then be meaningless, as we have no choice but to accept the conclusion of a logical proof.
Premise 1: CO2 traps heat and is largely responsible for the earth’s climate.
This is a simple scientific fact. Not even the 3% of scientists who disagree with climate change disagree with this premise. CO2 traps IR radiation, preventing it from leaving the earth. Without it, earth would be much colder. That is an irrefutable scientific fact.
Premise 2: We have greatly increased the CO2 in the atmosphere.
Again, this is an irrefutable scientific fact. We can measure past CO2 levels in the environment using ice cores. In certain parts of the world, ice forms annual layers, and air bubbles containing CO2 get trapped as those layers form. So we can drill into those bubbles Jurassic Park style and measure the past CO2 levels. Further, we can confirm that ice layers form annually by checking them against known volcanic events (ash from the volcanoes gets trapped in the ice layers, so we can check the date based on counting layers to the known dates of eruptions like Pompeii, and see that the dating method does work). So, using these data, we can tell that there is more CO2 in the atmosphere now than at any point in roughly the past 800,000 years.
Further, we know that this increase is from us because of the Carbon-13/Carbon-12 ratio. Carbon exists in three different isotopes (i.e., they have different numbers of neutrons), but Carbon-13 and Carbon-12 are the most abundant (Carbon-14 is unstable). The Carbon-13/Carbon-12 ratio that is naturally in the atmosphere is different from the ratio in our fossil fuels. So, if the in the increase in CO2 is from our fossil fuels, we expect the Carbon-13/Carbon-12 ratio in the atmosphere to shift to be closer the ratio in fossil fuels. Guess what, the ratio has shifted significantly, clearly demonstrating that we have altered the atmosphere and increased the CO2 concentrations (Bohm et al. 2002; Ghosh and Brand 2003;Wei et al. 2009). These isotope data are unambiguous. They are like fingerprints, and they trace back to us.
Premise 3: When you increase something that traps heat, you trap more heat.
This is thermodynamics 101 and should be intuitively obvious to everyone. If you didn’t accept this premise, you wouldn’t wear a thicker coat in January than you wear in April. Further, we have demonstrated many times in the laboratory that if you increase the CO2 concentrations, you will trap more heat.
Conclusion: Therefore, we are causing the climate to change.
This conclusion follows necessarily from the premises. CO2 traps heat, more CO2 traps more heat, we have greatly increased the CO2 in the atmosphere, therefore the earth is trapping more heat. This is irrefutable. It’s not opinion, it’s fact. Unless you can discredit one of these premises or show that a logical fallacy has been committed, you MUST accept the conclusion.
Finally, just in case someone isn’t convinced, I will offer one more piece of evidence. Energy from the sun enters the earth as high energy, short wavelength light. It leaves the earth as longer wavelength IR radiation, some of which gets trapped by CO2. So, if our increase in CO2 levels is causing the planet to warm, we would expect the input from the sun to remain constant, but the amount of IR leaving the earth should decrease. Note: this is an exclusive prediction. In other words, the ONLY way that you would get constant input but decreasing output is if greenhouse gasses like CO2 are trapping more heat. So, in the 70s we launched satellites to measure energy going in and leaving, and, lo and behold, the input from the sun has remained essentially unchanged, but the IR leaving the earth has decreased significantly (Harries et al. 2001; Chen et al. 2007; Griggs and Harries. 2007). Importantly, this decrease has been at the wavelength that CO2 absorbs, and the decrease correlates nicely with increasing CO2 levels. The only reasonable explanation for those data is that our CO2 is trapping more energy. This is a close to proving something as science ever comes. It is an incontrovertible fact that we are causing this planet to warm.