One major barrier to climate progress is ignorance. The climate crisis is immensely complex, and trying to make sense of even the basics of the manifold intersecting phenomena that now accelerate the Earth system towards broaching of key planetary boundaries is daunting. I have some imagined projects to that end that, for now, feel impractical (as they’d require data synthesis and visualization beyond my current appetite or capacity), so for the time being, I’m going to start writing up some very basic primers. My hope is that these may prove both useful and interesting to some readers, and that I’ll learn a lot in the process of writing them.
Okay: Greenhouse gases. What are they? Greenhouse gases are molecular compounds that, when present atmospherically, trap heat in Earth’s atmosphere. They do this owing to their molecular structures; my best understanding, to be more precise, is that the resonance frequencies of some of their bonds correspond to the wavelength of infrared radiation. A product of insolation (that is, exposure to solar radiation), this infrared (or IR) radiation – that would otherwise have been reflected off the surfaces (of land, water, ice, etc.) of the Earth back into “outer space” – is then instead retained in Earth’s atmosphere because it strikes the greenhouse gas molecules in the atmosphere, causes their bonds to “vibrate” and thus become more energetic. At a very macro level, when the balance of greenhouse gases in Earth’s atmosphere shifts, it can cause the planet to heat up or cool down as those of us alive today are now experiencing.
There are a great many greenhouse gases, but the one most talked about is obviously carbon dioxide (or CO2). Global atmospheric concentrations of carbon dioxide are measured in parts per million (or ppm). During the pre-industrial Holocene, these concentrations remained relatively stable around 270 ppm. Today, they are approaching 420.
In addition to carbon dioxide, methane (or CH4) and nitrous oxide (N2O) are also significant contributors to the current global heating being experienced on Earth, though their concentrations are both low enough to be measured in parts per billion (or ppb). Both of these gases are much shorter lived in Earth’s atmosphere than is carbon dioxide, but both of them also have much higher global warming potential (that is, they contribute more to the heating up of the planet on a per-molecule basis) than does carbon dioxide over a 100-year time horizon, which makes rising global methane and nitrous oxide emissions especially worrying at present.
There are also a number of halogenated compounds (many of them refrigerants) that are present in still lower atmospheric concentrations, but which have astronomically higher global warming potential than even methane and nitrous oxide. (Project Drawdown, a worthy endeavor that is also subject to criticism for its essentially neoliberal framing of climate action, has hence identified changes to refrigerant production, use, and disposal as the single most impactful step to be taken to combat global climate crisis.)
Finally, it’s worth noting that water vapor itself serves as a greenhouse gas, and atmospheric black carbon (aka, soot) also contributes to warming, while – ironically – some industrial pollutants, such as sulfur dioxide, actually lead, when present in the atmosphere, to a cooling effect (which is why maniacs who believe in geoengineering look to releasing sulfur dioxide in the stratosphere as a potential “solution” to global heating; more about geoengineering, solar radiation management, stratospheric aerosol injection, and other related topics in future posts).
That feels like enough for today. Anyone not already familiar with the Keeling Curve should reward themselves for finishing this post by having a quick look at the curve, data for which has been collected since the 1950s from atop Mauna Loa, at an observatory which stands on the occupied land of Native Hawaiians.
Note: Apologies for the lack of subscripts above. WordPress does not seem to allow for their easy insertion.