Greenhouse gases are called such because they trap heat that might otherwise dissipate through various processes. Just five greenhouse gases account for probably more than 95% of climate change effects. These five gases, from worst to least problematic, are:
1. Water
2. Carbon Dioxide
3. Methane
4. Nitrous Oxide
5. Ozone
For the most part, this post will talk about the top three offenders.
Water
Many people will be surprised to see "water" at the top of the list, but I'm not referring to liquid water. I'm referring to water in its gaseous form (known as water vapour). Most of the water vapour in our atmosphere is essentially invisible, unless there is a large quantity present. When water vapour becomes concentrated enough to become visible, you will perceive it as "haze," or see it even more obviously as clouds or steam. Some people assume that fog and mist are also made of water vapour. They're not. Fog and mist are comprised of small liquid water droplets suspended in the atmosphere, rather than water in its gaseous form.
The chemical formula for water, regardless of whether it is in liquid or vapor form, is H20. Ice (water in solid form) also has the same chemical formula. The only difference between the three states is the amount of energy that is contained in the molecules, which is represented by the temperature.
Climate change scientists disagree about many specific observations, although there is overwhelming consensus that climate change is real. Depending on the source, you may read that water vapor is responsible for less than half of global warming, or as much as three quarters of global warming. Regardless of which of those choices is closer to the truth, it's a large amount.
When explaining greenhouse gases (GHG's) to someone who is interested in the science, the first major intellectual frustration usually happens when people suddenly realize that water vapour in the air is responsible for the majority of greenhouse gas effects (and therefore, and therefore, water vapour is the biggest problem when it comes to climate change). People protest that we can't do anything about the amount of water vapor in the atmosphere. And you're right! Mostly right. There's not much we can do.
The amount of water vapour in the air varies significantly depending on where you are taking a sample. In deserts, the amount of water vapour is almost negligible. In rain forests, the atmosphere is heavily laden with water vapour. For this reason, we must consider global averages when we talk about the contribution of water vapour to global warming.
It is natural to have water vapour in our atmosphere. Water vapour is essential to life, for many reasons. For now, let me just say that the Earth's global ecosystem has been in a sort of historical equilibrium for the past several centuries whereby our planet had a "good" amount of water vapour in the atmosphere, but it was in balance. There was not so much water vapour that it caused problems with global warming. The real problems with global warming started to happen when we started increasing the amounts of GHG's #2 through #5 on our list.
Let's move on from water for now, although I'll have a few more comments about it at the end. For now, if you want to memorize one key talking point, focus on this: Water vapour is controlled by the Earth's temperature, rather than water vapour controlling the Earth's temperature.
Carbon Dioxide
We often refer to carbon dioxide by its chemical formula, CO2. Carbon dioxide is the gas that the public most commonly associates with climate change. That's a good thing. Carbon dioxide is the GHG that the general public should focus on when trying to mitigate the effects of climate change.
Carbon dioxide is composed of two substances (carbon and oxygen molecules) and the ratio is one molecule of carbon for every two molecules of oxygen. If this gas were broken apart into carbon versus "conventional" oxygen (in its diatomic homonuclear form, O2), the oxygen doesn't pose a problem. We could break carbon dioxide up into carbon and diatomic oxygen, and then hide the carbon away from the atmosphere (or just hide the CO2 itself from the atmosphere) and we'd have less problems with global warming.
We Interrupt This Bulletin to talk about the Atmosphere
No, the atmosphere wasn't on our list of greenhouse gases. Understanding the atmosphere is important, because it contains GHG's. Our atmosphere also contains lots of other gases. It also contains small amounts of liquids such as rain, and small amounts of solids such as smoke particles and dust.
A lot of us learned in high school that our atmosphere is composed of about 78% nitrogen gas (chemical formula N2), 21% oxygen (O2 form, not the single unbonded oxygen atom), a bit of argon, and trace amounts of several other gases including carbon dioxide. Nitrogen and oxygen in the atmosphere are called non-greenhouse gases. These non-greenhouse gases have special properties that mean they don't absorb infrared radiation, and therefore don't contribute to the greenhouse effect. Carbon dioxide DOES absorb infrared radiation, which is a problem.
Water vapour is not considered to be "part" of our atmosphere when scientists list the relative amounts of each constituent gas. Although this is confusing, we need to acknowledge that water vapour is IN the atmosphere, but it's not a defined part of it. When scientists talk about the makeup of the atmosphere, they assume that we're talking about dry air. If we had to give different atmospheric compositions depending on where we stood on Earth, our results would vary widely. Even a single point on the Earth would vary from day to day, depending on whether it was cloudy and raining, or clear and sunny.
When we talk about about water in the atmosphere, we have to consider both water vapour (gaseous form) and liquid water (rain, snow, mist, fog). Sometimes one turns into the other. Some water droplets evaporate. Gaseous water vapour often condenses to form water droplets. When trying to understand that water can be in the atmosphere but not part of it, you have to realized that the distinction is subtle. Think of baking a batch of chocolate chip cookies. If you think of nitrogen and oxygen and other gases as mixing up homogeneously, they are analogous to batter in the cookies before you add the chocolate chips. You can no longer identify individual ingredients such as sugar, flour, or eggs in the batter. The batter (like the atmosphere) is so well mixed that individual ingredients are no longer discernable. But water in liquid form (tiny droplets or fat raindrops) is akin to chocolate chips that you might add to the cookie batter. Even after mixing, you can readily identify the chocolate chips as being contained within the batter mix, even though you can't tell individual parts of the batter apart. There is a strong analogy between the chocolate chips and the water droplets.
Maybe that was too much of a tangent. Let's get back to our GHG's.
Methane
The chemical formula of methane is CH4. Methane is bad. Well, it's not bad in and of itself. It's a chemical. It's used beneficially for humans, for things such as heating and lighting and in the manufacture of useful other chemicals and products. It's only when methane escapes into the atmosphere that it starts causing a problem. This is where certain industries need to pay special attention.
How does methane escape? If escaped methane is the problem, can't we just be more careful with how we handle it? Well, no. A lot of the methane on earth occurs naturally. Methane is the natural by-product of decay in many swamps. We can't just fill in all the swamps around the world. Methane is also produced indirectly through human-made activities, in sewers, septic systems, and landfills. Methane is produced by living creatures. All those cows around the world release methane into the atmosphere every time they burp. And methane is also produced in the extraction and transportation of fossil fuels.
The biggest problem with methane is that even though there is much less methane in the atmosphere than carbon dioxide, it is many times more potent than carbon dioxide. Depending on whom you ask, methane is probably twenty to one hundred times more problematic than CO2. Perhaps we should think of methane as the "low hanging fruit" in trying to mitigate climate change, and tackle man-made sources of methane as our highest priority?
Another problem with methane is that it too exhibits a "positive feedback loop" as global temperatures rise. When the temperature rises, most living organisms tend to increase physiological activities (including the emission of methane). Swamps aren't the only water sources that naturally emit methane. Our freshwater lakes and rivers and streams and puddles are also a source, because they usually contain small organisms that emit methane. As temperatures warm up, methane emissions increase, which then cause further increases in global temperatures. It's a catch-22 situation. We need to get ahead of the curve, before it's too late.
The amount of atmospheric methane today (about 1.87 ppm) is approximately 2.5 times the amount that was present in the atmosphere during pre-industrial times.
Atmospheric Behaviour
Now that we know some of the basic characteristics of water vapour, carbon dioxide, and methane, let's look at how they act (and persist) within the atmosphere. In this respect, these three GHG's behave very differently.
As I alluded to above, we can't really control water vapour. Water vapour is controlled by temperature, rather than temperature controlling water vapour. The globe is essentially in a state of equilibrium when it comes to water vapour. The only minor exception is that as global temperatures rise, the average overall amount of water vapour in the atmosphere also rises (higher overall saturation of the atmosphere), so there's a small concern due to this positive feedback loop. But we need to look at the other GHG's to solve the problem. If we can reduce the effects of the other GHG's, the water vapour equilibrium will take care of itself.
Here's a trivia question for you: Can you guess how long water vapour remains in the atmosphere? Scientists believe that it is probably not much more than a week on average. This means that if a molecule of water "evaporates" from an ocean or lake, chances are that on average, it will return to the surface as rainfall or snowfall in just over a week. This is why water is so good at maintaining an overall temperature-based equilibrium. It's in a constant state of flux.
Carbon dioxide, unfortunately, does not return quickly to the Earth's surface. If it did, we wouldn't have these climate change problems (although we'd probably have a different set of problems). Carbon dioxide is removed from the atmosphere predominantly by photosynthesis, and also by being mixed into the ocean (carbonated surf?). But this process takes many years. Estimates are that even after one hundred years, half of any carbon dioxide that has been emitted into the atmosphere is still present up there, and still contributing to global warming. Even if we could completely stop emitting CO2 tomorrow, in 2069 the atmosphere would still have half of the carbon dioxide that's already up there (mind you, that would be a "sustainable" level). If reducing methane emissions is the "low hanging fruit" of climate change mitigation for certain industries, then reducing CO2 emissions could be called the "heavy lifting" (on a global scale), and almost everyone can help tackle the carbon dioxide problem.
Methane, our third significant GHG, is a big problem. Let's look at the positive side first: A lot of methane disappears from the Earth's atmosphere in about a decade, which is much faster than carbon dioxide. However, the negative side is that methane is MUCH worse than carbon dioxide when it comes to trapping heat (by worse, I mean that it traps heat more effectively, which is bad for humans who don't want climate change). If you compare methane and CO2 side-by-side in the first twenty years after release into the atmosphere, methane is almost ONE HUNDRED times as problematic. Even on a hundred-year comparison, methane is still the bigger problem. Now you understand why many people say that we need to reduce the number of cows on the planet. Or teach them to stop burping and be less flatulent.
Fun fact: NASA says that cow burps release more methane than cow flatulence, in case you wondered which end was the bigger problem.
Ozone
Again, a tangent. I said earlier that ozone is one of the top five GHG's, although to be fair it is far less of a problem than the top three. So if it's a problem, that must mean that "More ozone equals more warming," right? Yes, that's correct.
But right now, some of you are probably thinking, "Wait, if ozone is a problem, why did we ban CFC aerosol cans? Can't we just spray a lot of CFC's into the atmosphere and wipe out all the ozone, so the ozone stops contributing to global warming?" Well, yes, I guess that's an option. But the reason we banned CFC's was because we need ozone to protect us too. Even though it contributes to global warming, it protects us from deadly types of radiation. If we eliminate the ozone, we might be cooler, but we'd also have very high rates of skin cancer, eye cataracts, and damage to our genetic and immune systems. So please, let's not target ozone.
Summary
I think that I've covered all the basics. In point form:
- Water vapour is the main greenhouse gas, but since we can't do anything about it, don't think that we need to eliminate it.
- Carbon dioxide is second most common GHG, and since we can change the amount of carbon dioxide in the atmosphere through processes such as carbon capture methods, then it's a great target for climate change reduction.
- Methane is often overlooked because it's less prevalent than the two GHG's listed above, BUT since its effects are so much more significant than carbon dioxide, we should also target methane emissions wherever possible. This is especially important for certain industries such as oil & gas (ie. flare or capture associated natural gas, which is mostly methane, rather than venting it).
Thanks for reading this far. In a future post, I think I'll talk about carbon capture technology and ways to target methane emissions. In the meantime though, remember that trees act as a great filter for our atmosphere, because they help remove carbon dioxide. And that's why we like to plant trees. Please visit our website to learn more about our carbon capture and community forest projects.
- Jonathan Clark
www.replant.ca-environmental.ca
Incidentally, our organization is often seeking additional land for our carbon capture projects. Please visit this link if you might know of a recently-harvested property that we could rebuild into a permanent legacy forest.
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