Why Carbon Dioxide is the biggest devil of the atmosphere?
Climate Change poses the biggest threat to humans in our evolutionary history and Carbon Dioxide seems to be its biggest perpetrator. It should not make much sense at first glance when we analyze the percentage of Carbon Dioxide in the atmosphere compared to other gases. 78.1% of our atmosphere is composed of Nitrogen, 21% of Oxygen and 0.94% of Argon. That leaves about 0.04% for Carbon Dioxide and rest for other gases. That’s not a lot of Carbon Dioxide, is it? Moreover, Carbon Dioxide level was 0.028% before the Industrial Revolution, when climate change did not pose a threat. How can something so small, possess the ostentatious capability to destroy billions of years of evolutionary output. I mean there is 500 times more oxygen in the atmosphere than carbon dioxide, so why is it carbon that has manifested itself as the devil of human progress.
Carbon Dioxide isn’t the only gas responsible for Climate Change. Methane (CH4), Nitrous Oxide (N2O), water vapor (H2O) and chlorofluorocarbons are other antagonists of the show. All these gases, responsible for Global Warming (and ultimately Climate Change), are called greenhouse gases. If you every took a chemistry class (fret not if you did not), you should see fundamentally how greenhouse gases are different from non-greenhouse gases like Nitrogen(N2), Oxygen(O2) or Argon(Ar2): non-greenhouse gases are homonuclear and diatomic (having two atoms of the same kind) while greenhouse gases are heteronuclear (different kinds of molecules) and usually formed up of 3 or more atoms. And this gives greenhouse gases their power (both for preservation and destruction). To understand this fully, we will go into some molecular physics.
Molecules are created by bonding, i.e. by the process of sharing electrons between atoms. This sharing happens because atoms pull on electrons of other atoms. Some atoms are better at pulling electrons than others, like Oxygen is better at attracting electrons than Carbon. The ability to pull electrons is quantified by something called the “electronegativity” of an atom. Now, when atoms come together to form a molecule, electrons are shared and a molecular bond is formed. However, there is a tug of war between the atoms to pull the shared electrons. If the atoms are of the same kind, no one wins. However, if the atoms are of different kind (heteronuclear), then one atom often is able to pull the electrons more to their side. So, the shared electrons are closer to one atom than the other. This is called a “dipole”, one pole has less electrons hence slightly positive and the other has more electrons hence slightly negative. The amount of “dipoleness” is called the dipole moment. Molecules like Oxygen (O2) and Nitrogen (N2) have no dipole moment, however those like Carbon Dioxide (CO2) and water (H2O) do have a dipole on each of their bonds. Molecules with bonds that have a dipole moment are able to absorb heat through infrared radiation, however the ones without a dipole moment cannot. The physics of why that is the case is slightly complicated and we shall gloss over it.
Note: CO2 has zero net dipole moment even though each of its bonds has a dipole moment. That’s because of CO2's linear structure. That does not prevent CO2 from absorbing infrared radiation because the dipoles in the bonds of CO2 can still vibrate and that is the only requirement for absorbing infrared radiation.
The ability to absorb infrared radiation renders these molecules capable of causing the greenhouse effect. A broad spectrum of electromagnetic radiation continuously strikes the earth. Most of this energy comes in the form of short-wavelength infrared radiation, visible light and ultraviolet (UV) radiation. The UV rays are mostly absorbed by the ozone layer while the rest penetrate Earth’s atmosphere. Greenhouse gases only absorb long-wavelength infrared radiation and are transparent to visible light and short-wavelength infrared radiation. Thus, visible light and short-wavelength infrared radiation pass Earth’s atmosphere without hindrance and strike the Earth’s surface. They are absorbed and re-emitted at the surface. In this process, the radiation loses some of its energy, warms up the Earth’s surface a little and gets re-emitted as long-wavelength infrared radiation. The long-wavelength infrared radiation cannot simply escape now. They are absorbed by greenhouse gases and re-radiated back to the Earth. This warms up our planet. Without this phenomenon, the Earth would be a frozen ball. This entire phenomenon is called the greenhouse effect. Greenhouse effect is thus vital for life to exist on Earth. However, excessive greenhouse effect (also called global warming) causes severe problems.
Some greenhouse molecules are better than others at absorbing heat. For example, you might have heard methane (CH4) is a stronger greenhouse gas than (CO2). Why is that? It has to do with the number of atoms the greenhouse gas possesses. A molecule with more atoms has more “degrees of freedom”, i.e it can move is more ways than a molecule with less atoms. Having more degrees of freedom allows a molecule to store more energy. This is due to something called the theorem of equipartition of energy: energy gets equally divided among a molecule’s different degrees of freedom, hence a molecule with more degree of freedom can store more energy. Since methane has 5 atoms compared to carbon dioxide’s 3 atoms, it can absorb more energy than carbon dioxide and produce a stronger greenhouse effect.
All of this said, it should now make sense why the presence of excessive greenhouse gases is of great concern to scientists and non-scientists alike. However, among all the greenhouse gases, why Carbon? There are two reasons. First, there is a lot more carbon dioxide than methane in the atmosphere. Second, carbon dioxide is energetically highly stable compared to methane and thus lasts much longer in the atmosphere that methane does. All of this make Carbon Dioxide an unwelcome guest in the climate community.
Since the industrial revolution, countries have been emitting great amounts of Carbon Dioxide and other greenhouse gases into the atmosphere. This has raised average global temperatures noticeably by about 1⁰ Celsius. Global warming leads to Climate Change. And Climate Change renders the potential to disrupt Earth’s ecosystem in a way that puts the survival of the entire human species at great peril. Only nuclear warfare comes close to the destruction capability that global warming harnesses. At least with warfare, humans have the ability to ceasefire once our irrational brains realize the destruction that we have done. With nature, on the other hand, no such deal can be struck. If we continue our trends, nature will soon engulf us like the thousands of species it did in the mass destructions in the past.
