Carbon dioxide, methane, nitrous oxide and fluorinated gases but what about water vapour?

Photo by Guilherme Rossi

Written by Zeng Han Jun

 

I hesitated to write this… for about three weeks or so. In fact, there are always a lot of issues throughout the week for me to write about, but I usually let those issues seep in my brain for a while before I carefully pick one topic to write.  I almost dropped this topic but after weighing it, I decided to go ahead and write briefly about Greenhouse Gases (GHG) emission. I believe that we can bring about greater awareness on this topic if more people decides to step forward and share more information with one’s sphere of influence. 

 

So, you might think that it’s not a big deal to write about GHG emission. You know, the usual stuff like carbon emission that is covered under Scope 1, 2 and 3, other GHG emissions and ozone depleting substances. That is what most of the people have been harping on for quite some time but I want to go just a little bit further.

 

As you might already be aware, the race towards securing the next big idea of reducing carbon emission or extracting carbon content from the atmosphere, is very real. Big personalities are starting to showcase or have already showcased themselves, their organisations, their visions, their network in an attempt to attract the most pioneering ideas and the best talents. 

 

I imagine that some are howling at their staff over the phone or across the table and sending them to all corners of the globe to search for the next big idea or maybe also expecting them to squeeze their network dry. Like really dry, but somehow the same few ideas keep surfacing… from the same few groups of networks. Nah, it’s just my imagination. No one howls at anybody for such things right?

 

Right?

 

Anyway, a lot of companies have dead-locked their firing sights on carbon emission. I noted that a few companies have ventured to explore other ideas such as capturing methane and using the captured methane as fertilisers or fuel. 

 

Ok, before you yell at your staff over the phone to look for investments in methane capture technology. Please place your hand over your heart, take a few deep breaths, calm down and read about what I have to say further. 

 

There are many types of Greenhouse Gases (GHG) and the typically known ones are: 

  1. Carbon Dioxide; 
  2. Methane; 
  3. Nitrous Oxide; and 
  4. Fluorinated Gases.

The first one and also the one that most industries are interested in reducing, is carbon dioxide. This gas accounted for roughly 80% of all human-caused GHG emissions in the United States in 2019. Some of the excess carbon dioxide will be quickly absorbed (for example, by the ocean surface), but some will remain in the atmosphere for thousands of years, owing to the very slow process by which carbon is transferred to ocean sediments (Climate change, 2007). 

 

Next is methane, which has a much shorter lifetime in the atmosphere than carbon dioxide, but methane is more efficient at trapping radiation than carbon dioxide. Over a hundred year period, the comparative impact of methane is 25 times greater than that of carbon dioxide and this is why some companies have departed from the red ocean of carbon capture market and ventured into the blue ocean of methane capture market (Climate change, 2007). 

 

The third one is nitrous oxide, which accounted for approximately 7% of all human-caused GHG emissions in the United States in 2019. Nitrous oxide molecules linger in the atmosphere for an average of 114 years before being removed by a sink or destroyed chemically. One pound of Nitrous oxide has nearly 300 times the warming effect of one pound of carbon dioxide (Climate change, 2007). 

 

Finally, last but definitely not the least, fluorinated gases. Unlike many other greenhouse gases, this group of gases have no natural sources and are only produced by human activity. They are emitted as a result of their use as ozone-depleting substitutes (e.g., refrigerants) and a variety of industrial processes such as aluminum and semiconductor manufacturing. Because many fluorinated gases have extremely high global warming potentials (GWPs) in comparison to other greenhouse gases, small atmospheric concentrations can have disproportionately large effects on global temperatures. They can also have long atmospheric lifetimes, lasting thousands of years in some cases. Fluorinated gases, in general, are the most potent and long-lasting type of greenhouse gas emitted.

 

Precisely because these gases are emitted by the industrial sectors, it actually makes emission control much easier. We can track the emissions to its industrial sources, monitor the outputs, from there we would be able to understand what contributes to the outputs and then devise various methods to reduce or capture GHG. Additionally, regulators could make companies pay for the pollutive emissions and this encourages companies to invest and install emission control mechanisms to treat any industrial waste or air pollution before releasing these by-products into the ecosystem.

 

Companies should be willing to invest in these technologies as long as the total investment for the emission control mechanisms is less than what they need to fork out for any penalties or for as long as it makes financial sense. 

 

Ok, so that is all for carbon dioxide, methane, nitrous oxide and fluorinated gases. 

 

Now, I am going to talk about water. To be more precise, I am going to talk about water vapour. 

 

Water vapour is the most important gaseous source of infrared opacity in the atmosphere and an increasing number of works are showing that it is the dominant greenhouse gas. 

 

Water vapour concentrations are not directly influenced by human activities and vary regionally. However, human activities could increase global temperatures and water vapour formation indirectly, amplifying the warming in a process known as water vapour feedback (Soden, Jackson, Ramaswamy, Schwarzkopf, Huang, 2005).

 

Water vapour feedback can in turn amplify the warming effect of other greenhouse gases, such that the warming brought about by increased carbon dioxide allows more water vapour to enter the atmosphere. As the concentrations of other greenhouse gases, particularly carbon dioxide, rise due to human activity, it is critical to forecast how the water vapour distribution will change. 

 

The contribution of water vapour to the greenhouse effect in the Earth’s atmosphere far exceeds that from other gases, such as carbon dioxide, methane, etc. Calculations estimate that water vapour and clouds are responsible for 49% and 25%, respectively, for heat absorption (longwave absorption to be more precise but I will elaborate on this later). Carbon dioxide is responsible for about 20% of the heat absorption. Please note that the percentages of the greenhouse gases in our environment is not fixed and varies daily, seasonally, and annually (Schmidt, Ruedy, Miller, Lacis, 2010).

 

It is important to note that the difference between tropical and polar latitudes, for example, is determined not only by the difference in air temperature, but also by the difference in atmospheric water vapour (Chesnokova, Firsov, Razmolov, 2019). This goes to highlight the impact that water vapour has on the entire Earth’s atmospheric condition. 

 

Let me just briefly explain about the scientific model that is generally accepted by most of the scientific community at the moment.  

 

Electromagnetic radiation is emitted by everything that has a temperature. Shortwave radiation contains more energy, while longwave radiation contains less. For example, the sun emits shortwave radiation because it is extremely hot and has a lot of energy to give. The radiation that is emitted by Earth, on the other hand, is longwave because it is much cooler, but it still emits radiation.

 

FIGURE 1

Simplified scheme showing greenhouse gasses (GHG) and their effects on plants. GHG (H2O vapour, clouds, CO2, CH4, N2O, and NO) have both natural and human origin, contributing to the greenhouse effect. Short-term effects of GHG increase is mainly CO2 rise, which activates photosynthesis (PS) and inhibits stomatal opening (SO). Long-term effects of GHG increase are extreme climate changes such as floods, droughts, and heat. All of them induce the generation of reactive oxygen species (ROS) and oxidative stress in plants. Nitric oxide (NO) could alleviate oxidative stress by scavenging ROS and/or regulating the antioxidant system (AS). GHG and volatile organic compounds (VOC) react in presence of sunlight (E#) to give tropospheric O3. Although tropospheric O3 is prejudicial for life, stratospheric O3 is beneficial, because it filters harmful UV-B radiation. The size of arrows are representative of the GHG concentration.

 

Clouds and the Earth’s surface absorb solar energy once it enters the atmosphere. The ground heats up and re-emits energy in the form of infrared rays and this is known as longwave radiation. Simply put, the Earth is cooler than the sun and has less energy to give off, it emits longwave radiation.

 

The radiation balance and atmospheric circulation are determined by the fluxes and inflows of shortwave and longwave radiation within the Earth’s atmosphere. Radiative processes, such as cooling or heating of the Earth’s atmosphere and surface, are actually heavily influenced by cloud parameters. 

 

A growing body of studies are pointing to the link between the formation of cirrus clouds and its potential impact on climate change. Cirrus clouds condense and nucleate on very specific mineral and metal particles high in the atmosphere. Although it is known that only a small percentage of atmospheric aerosols are efficient ice nuclei, the critical ingredients that make those aerosols so effective have yet to be established (Cziczo, Froyd, Hoose, Jensen, Diao, Zondlo, Murphy, 2013).

 

For us, we just have to note that several observations are showing that these clouds can roughly cover up to about 20% to 30% of the Earth’s atmosphere at any given time. Depending on their location in the atmosphere, they can either help cool the Earth or warm it up. Unlike liquid water clouds, which generally cool the Earth by reflecting sunlight, ice clouds might help warm it up by absorbing reflected heat (LiveScience, 2009). The contribution of cirrus clouds to the downward flux at the surface level is small, and the flux is determined by the emission of the gas components of the atmosphere, whereas the contribution of cirrus clouds is decisive at the top of the atmosphere. 

 

Cirrus clouds with small optical thickness enhance the greenhouse effect. Current research showed that the crystal particles within the cirrus clouds can emit more energy than water vapour, in that they cool the atmosphere by absorbing and scattering shortwave solar radiation while increasing longwave radiation. Water vapour, carbon dioxide, and other greenhouse gases absorb and trap this longwave radiation, causing the Earth’s surface and lower atmosphere to warm naturally. It is critical to understand that greenhouse gases do not trap incoming shortwave radiation, but rather longwave radiation emitted by the Earth’s surface and other mediums (Pacific Islander Council on Climate Change). 

 

Water vapour will increasingly play a significant role in the coming centuries. Climate models, backed up by satellite data, predict that as temperatures rise, the amount of water vapour in the upper troposphere (about 5 to 10 kilometres up) will double by the end of the century (Soden, Jackson, Ramaswamy, Schwarzkopf, Huang, 2005).

 

This will produce roughly twice the amount of warming as if water vapour remained constant. Cloud changes could amplify or reduce warming but there is a lot of uncertainty about this. Currently, we still cannot directly control the amount of water vapour in the atmosphere because water is found everywhere on our planet. It covers roughly about 70% of the Earth’s surface. To control the amount of water vapour in the atmosphere and the temperature of the Earth, we can only limit the greenhouse gases that we can actually control at the moment.

 

Anyway, when things become more stable, I would like to go back to Dubai again and try those new water dispensing machines that are placed outside their shopping malls. These new water dispending machines distill water directly from air and is safe to drink on the spot!

 

References

(n.d.). Retrieved from Account, S. (2013, June 03). The origins of cirrus: Earth’s highest clouds have dusty core. Retrieved from Cassia, R., Nocioni, M., Correa-Aragunde, N., & Lamattina, L. (2018, March 01). Climate Change and the Impact of Greenhouse Gasses: CO2 and NO, Friends and Foes of Plant Oxidative Stress. Retrieved from Climate and Water Resource Case Study. (n.d.). Retrieved from http://www.soest.hawaii.edu/mguidry/Unna… 2/Chapter2B2.html

Climate change 2007: The physical science basis. (2007). Cambridge University Press.

Contribution of the water vapor continuum absorption to radiative balance of the atmosphere with cirrus clouds. (2018). Оптика атмосферы и океана, (9). doi:10.15372/aoo20180908

Cziczo, D. J., Froyd, K. D., Hoose, C., Jensen, E. J., Diao, M., Zondlo, M. A., . . . Murphy, D. M. (2013). Clarifying the Dominant Sources and Mechanisms of Cirrus Cloud Formation. Science, 340(6138), 1320-1324. doi:10.1126/science.1234145

Ingram, W. J. (2012). Water vapor feedback in a small ensemble of GCMs: Two approaches. Journal of Geophysical Research: Atmospheres, 117(D12). doi:10.1029/2011jd017221

Main, D. (2013, May 09). How Cirrus Clouds Form – And Why It Matters. Retrieved from Schmidt, G. A., Ruedy, R. A., Miller, R. L., & Lacis, A. A. (2010). Attribution of the present-day total greenhouse effect. Journal of Geophysical Research, 115(D20). doi:10.1029/2010jd014287

Soden, B. J., Jackson, D. L., Ramaswamy, V., Schwarzkopf, M. D., & Huang, X. (2005). The Radiative Signature of Upper Tropospheric Moistening. Science, 310(5749), 841-844. doi:10.1126/science.1115602

Soden, B. J., Jackson, D. L., Ramaswamy, V., Schwarzkopf, M. D., & Huang, X. (2005). The Radiative Signature of Upper Tropospheric Moistening. Science, 310(5749), 841-844. doi:10.1126/science.1115602

 

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