Behind Climate Change: When Enough is Enough! – PhotoNick

By CoperNick

Alessandro Santoni 

 

April 29, 2019


 

In the last few decades, climate change has been among the hottest topics in political, ethical and environmental discussions, with the unveiling of its causes hitting the Web and the shadow of its effects crawling on the near future. People have been increasingly involved in this thread: from the youngest, as the little Greta Thunberg [1], to the oldest have participated to largely popular events like “Friday for future”, the mass manifestation that took place the last 15th March in the squares of cities all around the World.

If there is something clear to (almost) all scientific community, it is that climate change is real and that it is mainly caused by some human thirsty activities [2] and not only by the natural variations in the Earth’s ecosystem. In 2017 more than 15 thousand scientists from around the globe signed a warning to humanity. They stated: “The current trajectory of potentially catastrophic climate change due to rising greenhouse gases from burning fossil fuels, deforestation, and agricultural production – particularly from farming ruminants for meat consumption” is “especially troubling” [3].

However, this article will not deal with climate change itself, with man’s fault or the methods to possibly prevent it [4]. We will better discuss one of the mechanisms that significantly contribute to Global Warming: the well-known “Green-house Effect”. Each of us has probably heard about it sometimes recently, but how does it really work? For, as it is often said:

“If you know the enemy and know yourself, you need not fear the result of a hundred battles.”

[Sun Tzu, The Art of War]

First of all, we have to understand, how different molecules interact with light radiation. Molecules, as we know, are particles composed by two or more atoms bounded together in some particular way. From Quantum mechanics, it follows that they can absorb light to “promote” their electrons to higher electronic (quantum) states or to excite roto-vibrational modes [5], which involve the molecules’ oscillation and rotational motion.

 

Figure 1: Spectrum of molecule’s states and possible different excitations

 

As shown in the image above, the energy needed for the excitation, and indeed the frequency of the incident radiation to be absorbed, increase from the rotational (microwave) and vibrational (infrared) levels to the electronic ones (optical and UV). The peculiar thing about this phenomenon is that not all molecules are capable to excite all those different modes: in particular, homonuclear biatomic molecules like molecular oxygen and nitrogen – which compose the 9

Figure 2: Sunlight spectrum as a function of light’s wavelength.

 

There is still a very tiny percentage of the atmosphere where we find a different type of molecules: the heteronuclear ones, like H2O, CO2 and others! Due to some mathematical reasons, heteronuclear molecules can excite their own roto-vibrational modes, meaning that they can absorb and then emit light in the microwave-infrared range. And this makes all the difference! During the day some of the sunlight pass through the atmosphere because it has its intensity peak in the visible, to which the atmosphere is almost transparent, and for which it behaves as a half-reflecting surface. Thus, some solar radiation warms up the Earth. Instead, at night, the heat absorbed during the day is re-emitted in the form of infrared radiation. Only the so called “greenhouse gases”, thanks to their heteronuclear nature, can absorb some of this radiation and send it back to the Earth, allowing the temperature to not decrease too much and therefor to keep a (more or less) suitable environment. Without it, at night, we would have a thermal excursion way too big for life as we know it today.

Figure 3: Journey of sunlight in the atmosphere and on Earth.

 

The mechanism that allowed life to evolve and spread till today on Earth is also the one that now is (rightly) scaring us: “Not every cloud has a silver lining”.

If this is the case, why should we worry so much to reduce the emission of greenhouse gases? Some gases self-regulate themselves, like H2O: in small ranges of pressure and temperature around the normal values it changes its state from liquid to gas and come back to Earth in the form of rain. On the contrary, other gases like CO2 do not condense. Once they have been emitted in the atmosphere they stay there and rack up: so, they slowly (but inexorably) contribute to increase global temperature, along with all its consequences.

I would like to conclude this article with a quote:

“Today, we can see with our own eyes what global warming is doing. In that context it becomes truly irresponsible, if not immoral, for us to not do something.”

[Joe Lieberman]

To know more about effect of increasing Earth’s temperature you can go on the site of the “Intergovernmental Panel on Climate Change” [6], where you can find a special report on the “Global warming of 1.5°C” and lots of other interesting information.

 

References:

[1] https://www.ted.com/talks/greta_thunberg_the_disarming_case_to_act_right_now_on_climate?language=it

[2] https://scholarworks.uark.edu/cgi/viewcontent.cgi?referer=https://scholar.google.it/&httpsredir=1&article=2183&context=jaas

[3] https://academic.oup.com/bioscience/article/67/12/1026/4605229 

[4] https://academic.oup.com/reep/article-abstract/12/2/324/5035034?redirectedFrom=fulltext

[5] https://www.britannica.com/science/excitation

[6] https://archive.ipcc.ch

 

Images’ credits:

https://d2jmvrsizmvf4x.cloudfront.net/byYZP1cQruO0BJqrnSIo_1024px-Earths_greenhouse_effect_US_EPA_2012.png

https://chem.libretexts.org/@api/deki/files/125629/CNX_UPhysics_42_02_Trans.jpg?revision=1

http://wtamu.edu/~cbaird/sq/images/sunlight_wavelength.png

 

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