Even though humans are a highly technologized species, we are just as dependent on our environment as we have always been: from the air we breathe to the food we eat. It is therefore of crucial importance to study and to understand our environment in order to achieve a sustainable technological development, one that doesn’t threaten our very existence.

Atmospheric sciences, unlike the more traditional areas like physics and chemistry, whose models are used and applied on large scale real systems, are rather new branches of science, but the importance of the problems they are trying to tackle fully justifies the interest they have gained in the last decades. Atmospheric science had a slow start because of the inherent difficulties that are associated with it: although the underlying physical principles are rather simple, at least in qualitative terms, a quantitative analysis proves to be very difficult, complex models of the atmosphere being practically impossible to analyze without the heavy use of computers. However, simple models can be derived from those basic physical principles, and that’s exactly what great men of science had done throughout history. In order to better understand the current state of atmospheric science, its role in the description of climate change and the future of this scientific discipline, it would be a good idea to start from the foundations to the top, to follow the train of thought that gave us our current understanding of the atmosphere and its response to human activities.

The first scientist that realized the importance of the atmosphere with regard to the global climate and the average Earth temperature was Joseph Fourier. In the early XIX century he asked himself a rather simple question, but with a complex answer: if the Sun continuously warms the Earth, why isn’t the Earth getting increasingly hotter, until it would reach the same temperature as the Sun? Although very little was known at the time about heat and radiation, he concluded that the Earth emits some sort of invisible radiation (today we call this infrared radiation) that carries the heat with it. He also arrived at the conclusion that the Earth would be much cooler without its atmosphere, which he regarded as “a blanket” that traps heat. Actually, it was Fourier who proposed the analogy between the atmosphere and a greenhouse, which later became coined as the (in)famous “greenhouse effect”. Of course, Fourier’s analogy is rather farfetched, as we today know that a greenhouse traps the actual heated air, where the “greenhouse gases” from the atmosphere are responsible for trapping the heat radiation. Indeed, some 40 years later, John Tyndall discovered this effect of some gases (water vapors and CO₂) and consequently he was able to give a better analogy of how the atmosphere works in trapping the heat that tries to leave the Earth surface. He compared the Earth atmosphere with a dam, and concluded that certain gases from the atmosphere are absorbing the heat, thus raising the temperature above Earth’s surface just like a dam raises the level of the water uphill. Even if this simple explanation is not entirely accurate, its main idea is correct. In fact, only a century after Tyndall’s discovery scientists where able to fully explain this process of heat absorption.  However, using this remarkable discovery, other scientists were able to give increasingly better models that tried to explain the global climate and the influence that the atmospheric composition has on it. This is the case of the Swedish chemist Svante Arrhenius, who published in 1896 the first comprehensive that shows how the amount of CO₂ in the atmosphere may affect the Earth’s climate. He was able to go beyond this predecessors by taking into account the fact that the earth, the water and the other gases in the atmosphere are interconnected, and that a change in one of this factors has an effect on the others, effect that may amplify or reduce the initial change. Today, this mechanism is known as “feedback”. This piece of marvelous physical insight allowed Arrhenius to spot the actual major greenhouse gas: water. Arrhenius realized that the CO₂ in the atmosphere acts as a throttle that controls the level of the really important greenhouse gas, water. The amount of water on Earth is far larger than that of CO₂, but the water has a rapid cycle: it may go through its three states in a matter of days, where CO₂ can remain in the atmosphere for centuries. So a raise in the levels of CO₂ would produce a slight global warming, but this slight warming would make the air hotter, and hotter air holds more water as vapors, thus greatly enhancing the global warming set in motion. Arrhenius actually foresee a possible large scale global warming and he determined that a double amount of CO₂ in the atmosphere would raise the average global temperature by 5-6 . Modern calculations show that the increase would actually be of around 2-3 . It is important to note that Arrhenius got this correct order of magnitude result partially by luck: his model was rather faulty, with the main caveat being its “static” nature. He did not take into account important factors, such as the modification of the Earth’s albedo, oceanic and vertical atmospheric currents. However, we should give Arrhenius the credit he deserves: even with his simplified model, he struggled for months on end with his calculations, and the factors that he left out were actually impossible to be quantitatively analyzed in his time.

This historical walkthrough brings us to more modern times. In the second half of the twentieth century, scientists were able to grasp the actual mechanisms of global warming. The key is to note that the atmosphere is not made up of a single, thick, layer of gas, but actually consists of many, more thin layers with different proprieties. The radiation emitted from the surface of the Earth moves upwards, layer by layer, and some part of it is absorbed by molecules of greenhouse gases in each layer. This molecules may transform this absorbed radiation directly into kinetical energy, thus directly increasing the temperature of the respective layer, or it may radiate it in a random direction. Some of it will go back towards the ground, at some will go towards the upper layers. This process repeats itself, until eventually in the thinner layers of the higher atmosphere the energy may go directly into space, as the atmosphere is rarefied and there are no other molecules that may reabsorb it. So by adding more greenhouse gases, the higher layers will absorb more heat, thus shifting upwards the point from which heat radiation may escape into space. As the higher layers radiate energy towards the Earth, the lower layers will heat up in the process, and this feedback between the layers of the atmosphere will force a new equilibrium to establish, but until then the planet takes in more heat than it radiates (as the case is for Earth since the 1970s).

The other important augmentation that allowed scientists to better understand the atmosphere and to quantitatively analyze climate change is the use of computers. With high processing power, comes great benefit. For example, meteorologists are now able to prescribe the weather with relatively high accuracy thanks to modern computers. Of course, there is a huge difference between a local prediction of the weather for a couple of days and global climate evolution for decades.

We may now start to tackle one of the key questions: is global warming really happening? Indeed, global warming has been a subject of great controversy throught history. Initially, not even men of science thought that humans could have a long lasting impact on the global climate. It was indeed hard to think that a small alteration of the atmospheric composition due to human activity could increase the global average temperature by a few degrees. Early climatologists considered that Nature will balance the increase of CO₂ amount caused by humans (and it was a reasonable assumption, as the levels of CO₂ emitted from human activities was relatively low a century ago). After better models were available, climatologists started raising alarms in the media, but lobby from oil companies fueled conspiracy theories. Unfortunately, only about half of the human population believes that global warming represents a serious concern, and there still are groups of people or media outlets that doubt the reality of global warming, or call it “a hoax”. The truth is that an overwhelming quantity of independent scientific data points to the unescapable conclusion: the planet is getting warmer because of humans activities.

Climate models predict that during the XXI century, the average global temperature will increase in the best case scenario with 0.3 , a worst case scenario being an increase of almost 5 . Over the twentieth century, the average temperature rose by about 0.8 , and every year since 2000 has been at the respective moment the hottest year in the recorded history of global temperatures. Besides this direct evidence, there are also other observations such as increasing sea levels, accelerated melting of glaciers, earlier timing of spring events, that when corroborated leave no doubt about the reality of the global warming we are experiencing.

Unfortunately, as stated before, greenhouse gases such as CO₂ or CH₄ have a “high inertia”, meaning that they will remain in the atmosphere for hundreds and thousands of years. In fact, even if emissions of greenhouse gases were completely halted today, the warming trend would still continue. This is not by a long shot the case, with the most recent development in the area of cutting greenhouse gases emissions being the Paris Agreement, that will only begin to take effect from 2020. It is therefore expected to witness in the following decades increased effects of the global warming. With the continuous increase in global temperature, we can safely predict that glaciers will continue to accelerate their melting, and this fact will continue the ongoing rising sea levels. In fact, it is estimated that in the next 2000 years there will an approximate increase o sea level of 2 meters for every Celsius degree of temperature increase. On the other hand, temperature increase will accelerate the desertification that already takes place in some areas of the globe. Extreme weather events, such as the notorious 2003 heat wave that had a drastic toll on Europe, are also more likely to increase both in frequency and in intensity. The oceans act as a CO₂ buffer, absorbing large quantities of gas from the atmosphere. This leads to an increase in the world’s oceans pH, a 5% increase being projected for 2100. It is also believed that the pH was never higher that 8.1 in the past millions of years, so this dramatic increase raises serious concerns regarding marine wildlife. Coral reefs decay is already being observed more and more often in representative areas around the globe.

Seeing this chain of events triggered by the increase of CO₂ emissions, it is natural to ask ourselves how this changes will affect the human population in the future. In the future millenia, many costal areas would be underwater, and with some of the most populated areas being on the coast of various oceans, this raises serious problems regarding relocation of such high number of people. Until that stage, there are others factors to consider. The increase of extreme weather events is expected to have a more significant death toll on the human population affected. As temperature increases, the way of life of many people, especially in the low latitudes will be changed, with winters getting shorter and warmer. A possible effect of the global warming is represented by the slowing or even complete shut down of oceanic currents, such as the Gulf Stream, event that would trigger severe climate alterations in Europe and North America. As stated in the introduction, humans are dependent on their environement with regard to their food supply. Climatic change is expected to impact crop productions of the vulnerable, highly temperature dependent, cultures. A possible solution to prevent such events would be to genetically engineer crops to be more resilient to the increasing temperatures and the eventual drought. However, wildlife is expected to be serverly affected. Sustained global warming dooms many species to extiction, both on land and in the seas. The hidrosphere acts as a buffer not only for CO₂ but also for heat, with 93% of the extra energy the Earth has due to its state of radiative imbalance being stored in the global ocean (by comparison, only 1% of this energy is stored in the atmosphere), and the increase of pH and temperature will prove fatal for many marine creatures.

In order to be prepared for this combination of unwanted effects that we are facing, we must firstly better understand them. To achieve this better understanding, continued study of the complex atmospherical processes is required. As mentioned earlier, a huge impediment to Arrhenius was the lack of reliable data and, more importantly, the lack of computers. Modern computers have allowed climatologists to come up with current understanding of the atmosphere and of the global warming, but even the most advanced computers are still not enough for a more profound understanding. All climate models use certain simplifications, otherwise no predictions could be computed. In this context, a hardware improvement of existing computers is required, with a consequent expanding of the climate models used. Once a better understanding of climate change is achieved, we can investigate more efficient means of halting or even reversing some of its effect. Of course, the first step would be to massively reduce greenhouse gas emissions, but there may be other means in which we could help Nature to reestablish equilibrium. The first thing that comes to mind is reforestation, a relatively fast and reliable way of reducing atmospheric CO₂. Different climate engineering scenarios are also proposed, however more research is needed in this field, as current estimation show a very limited effectiveness of these techniques.

Now that we have a big picture of the global warming, we can understand the importance of atmospheric science. Since the Industrial Revolution, humanity has altered the environment in dramatic ways, and we have left our mark on the atmospheric composition for thousands of years to come. Our chaotic actions threaten the existence of a great number of species, and it is our duty to try to limit this consequences. By continued study of climate change we shall know what to expect, how to try to prevent or maybe reverse the effects of the ongoing global warming and how to preserve as much of the Earth as we can for the future generations.

REFERENCES

Tyndall, John (1873). “Further Researches on the Absorption and Radiation of Heat by Gaseous Matter (1862).”

Tyndall, John (1863). “On Radiation through the Earth’s Atmosphere.”

Arrhenius, Svante (1896). “On the Influence of Carbonic Acid in the Air Upon the Temperature of the Ground.”

Anders Levermann, Peter U. Clark, Ben Marzeion, Glenn A. Milne, David Pollard, Valentina Radic, and Alexander Robinson (13 June 2013). “The multimillennial sea-level commitment of global warming”

“Joint Science Academies’ Statement”

Stokes, Bruce; Wike, Richard; Carle, Jill (5 November 2015). “Global Concern about Climate Change, Broad Support for Limiting Emissions: U.S., China Less Worried; Partisan Divides in Key Countries”

Boden, T.A., G. Marland, and R.J. Andres (2010). “Global, Regional, and National Fossil-Fuel CO2 Emissions”

IPCC (November 11, 2013): D.3 Detection and Attribution of Climate Change

P. Keller, David; Feng, Ellias Y.; Oschlies, Andreas (January 2014). “Potential climate engineering effectiveness and side effects during a high carbon dioxide-emission scenario”