I use to travel by plane every year, sometimes for holiday; sometimes for business. Everytime when I am up there I take a look out of the window and I see the clouds just below the plane I am in. They appear to be objects, sometimes fluffy as if made of wool, and sometimes denser, as if they might be a floating mountain. On domestic flights in EU area sometimes the sky is clear and I even see the ground from high altitude without any cloud at all. Yet when I fly overseas, at one moment there is always this white blanked of clouds up there.
It was like that all the time when I traveled to from my hometown Brussels to New York. Observing the clouds from above, I understand that they are the reason why we have different weather condition on the ground, why there is a cetain temperature during the day and another one during the night. And of course clouds are the reason why rain occurs. But:
- WHAT are the CLOUDS made of?
- WHY they have so much influence on our life on the ground?
Let’s find out, keep reading the text below.
Anytime when a plane approaces to its final destination and preparing for descend the followings happen just like in my case traveling to New York:
In a relative silent cabin environment, all of the sudden I hear a Bong from the intercom, followed by a cabin crew announcement:
“Ladies and gentlemen, as we begin our descent into the New York area, please make sure your seat backs and tray tables are in their full upright position, that your seat belt is securely fastened, and all carry-on luggage is stowed underneath the seat in front of you or in the overhead lockers. Thank you.”
The plane was descending now, and my ears were beginning to pop. I had that feeling of anticipation—that my life was going to start again after the suspended animation of airplane flight. This journey had pressed the pause button on my life, in exchange for a taste of omnipotence. Up here, the clouds couldn’t rain on me; they couldn’t tyrannically blot out the light and sway my mood as they do when I am at home in Brussels. Up here, the light streamed in through the window, warming my face with a glow from a sun that never set. Never, that is, until the plane suddenly descended into the cloud layer; then, not only did the sun disappear, but it was abruptly replaced by a white haze that knocked all sense of omnipotence and security out of me: white out!
The cloud we had descended into, like all clouds, was comprised of liquid droplets of almost pure water. The almost bit is interesting; it’s the reason why rainwater isn’t pure, why windows get stained by rain, and why fog forms in some places and not others. The water in clouds is neither pure nor innocent—it can kill.
Night and day, somewhere on the planet, lightning storms are raging, at a pretty constant rate of 50 lightning flashes per second, globally. It’s estimated that there are more than a 1000 human deaths by lightning per year, with the injured numbering in the tens of thousands. The US National Weather Service keeps a running total of the deaths, and the particulars of the fatalities.
Number of deaths and injuries due to lightning in the U.S. from 1995 to 2021
The table below shows some of the entries for from 2016. You’ll see that taking shelter under a tree is not a good idea, and that danger can strike almost anywhere.
A table of deaths caused by lightning in the United States, collected by the National Weather Service
But can lightning get to you on a plane?
That is a question worth answering. Clouds start off as wet laundry on a line, as a puddle on the pavement, as a glow of perspiration on your upper lip, as part of a vast ocean of water. Every second, some of the H2O molecules leave wet laundry, puddles, upper lips, oceans, and other bodies of water, and make their way into the air. The boiling point of water is 100ºC, denoted as the temperature at which pure liquid turns into a gas at sea level. So:
- How does liquid water become a gas without reaching this temperature?
- What’s the point of defining the boiling point if water can cheat and dry laundry and upper lips, evaporate puddles, and denude oceans autonomously, at much lower temperatures?
As it turns out, the definitions of solids, liquids, and gases are not as clear-cut as they might seem, and the game that scientists play, of categorizing the world and making neat distinctions between different things, is constantly being sabotaged by the complexity of the universe. To understand how water cheats the system to create clouds, we have to think about an important concept called Entropy.
The water clinging to your laundry on a clothesline is below 100ºC in temperature, but it is in contact with air. The molecules in the air bombard your washing, crashing into it as they move chaotically; occasionally, in all the mayhem, an H2O molecule pings off to become part of the air. It takes some energy to do this, as the bonds that attach the H2O molecules to your wet clothes have to be broken. Taking the energy away from your clothes cools them, but it also means that if the H2O molecule floating around in the air were to collide again with your washing, it would gain energy by sticking to it, thus making it wetter again. So on average you might think that more water would stick back onto your clothing than would be carried away by the air currents of the wind. But here’s where entropy comes into play.
Because the amount of air billowing around your laundry is so great, and the number of water molecules is so low, the chances of a water molecule finding its way back onto your favorite cotton T-shirt is small. Instead, it is more likely to be whizzed up into the atmosphere. This propensity of the world of molecules to get jumbled up and spread out is measured by the entropy of the system. Increasing entropy is a natural law of the universe, and it opposes the forces of condensation that bond the water back onto your washing. The colder the temperature and the less exposed your laundry is to the wind, the more you tip the balance in favor of condensation, and your washing stays wet. In contrast, by hanging your washing on a line on a warm day, you tip the balance in favor of entropy, and your clothes get dry.
Entropy is the metric which measures the impurity of something or in other words you can say that checking entropy in a dataset is a 1st step to do before you solve the problem.
- A thermodynamic equilibrium (same temperature) –> heat flow stops
- All systems tend to go from low entropy to high entropy
- Everytime heat is exchanged entropy goes up (the availability of heat declines)
Entropy also takes care of puddles in the street, dries your bathroom after you’ve been in the shower, and removes the sweat from your body on a hot day. All in all, entropy seems very convenient, and generally quite helpful, given how much we like having dry clothes and bathrooms, and cool bodies. But that same benevolent force also drives the killer clouds that strike us down in the thousands every year by throwing their lightning bolts around, reminding us who’s really the boss in our atmosphere. The process of thundercloud formation starts with vaporized H2O, which moves around as a gas. Hot air rises because it’s less dense than cold air, so on a sunny day the water molecules make their way from your washing up into the atmosphere. The air, though full of water, is transparent, so at first there won’t be any sign of a cloud. But as the vapor goes higher, the air expands and cools, and the thermodynamic balance is tipped toward H2O molecules preferring to condense and be part of a liquid again. But a single molecule can’t just turn back into liquid in midair; to form a tiny droplet of water requires some coordination—several H2O molecules all have to come together to become a single droplet.
In the chaotic, turbulent atmosphere, this doesn’t happen easily, but the process is expedited by the tiny bits of particulate matter that are already in the air —often small bits of dust that have blown off trees and plants, or smoke from factory chimneys. The H2O molecules can attach themselves to these, and as more and more of them join together, the particle becomes the center of a tiny droplet of water. This is why when you collect rainwater, it generally contains sediment, and why when the rain dries onto your car windshield or the windows of your house, it leaves a fine powder.
This piece of physics was at the heart of one of the most extraordinary experiments of the 20th century—when scientists took it upon themselves to control the weather. The method was called cloud seeding, and it was invented in 1946 by Vincent Schaefer, an American scientist. Schaefer and his team determined that if you dispersed silver iodide crystals into the atmosphere, they would act as dust or smoke might, and become the nucleating droplets —the seeds—of clouds, which would, in turn, produce snow and rain. The technique is an art as much as it is a science, but as widely used as it’s been for decades, many dispute its effectiveness. Still, though, the USSR seeded clouds over Moscow every year. Their aim was to clear moisture from the air by making it rain, ensuring that their May Day celebrations were accompanied by blue skies. The US military employed the technique for a different aim during the Vietnam War—they used it to extend the monsoon season on the Ho Chi Minh Trail; this was called Operation Popeye, and its mission was to “make mud not war.”
Today countries around the world, like China, India, Australia, and the United Arab Emirates, all experiment with cloud seeding as a means to tackle drought conditions. Of course, by seeding the air you control only one aspect of the weather: cloud formation. So if the moisture content of the air is low, no amount of cloud seeding will make it rain. But if the air is full of water, then using this technique to increase snowfall over ski resorts, or reduce the risk of hail damage on crops during storms, can be productive. In the aftermath of the Chernobyl nuclear disaster in 1986, cloud seeding was used to make enough rain to remove radioactive particles from the atmosphere.
Airplanes don’t need to use silver iodide to seed clouds. If you look up into the sky on a sunny day, you’ll often see contrails emanating from the back of a jet aircraft. This isn’t smoke spewing out of a badly maintained engine; it’s a cloud seeded by the engine emissions. Small particles from the combustion process are emitted from the plane, along with an enormous amount of very hot gas. The gas pushes the aircraft forward, and while you might expect it to be too hot for water to form, at high altitudes the temperature is so low that the exhaust is quickly cooled. The emission particles become sites of nucleation for liquid droplet formation, which then freeze, first becoming water, and then tiny ice crystals.
Contrails are just high, wispy cirrus clouds. Depending on conditions in the air, contrails might last for just a few minutes, or maybe for a few hours, and the sheer number of them (there are a hundred thousand flights per day, globally, all producing contrails) has led many to suspect that contrails must have an effect on Earth’s climate. Common sense tells you that clouds cool our planet; if you’ve sat on the beach on a cloudy day, you’ll have experienced this. But clouds don’t just reflect sunlight back into space. They also trap heat from the ground, in the form of infrared waves, and bounce it back to Earth. It’s an effect that’s particularly noticeable in winter, when clear skies create colder conditions than cloudy skies, because at night the heat that’s lost from the ground is bounced back by clouds. And different cloud types (distinguished by color, density, and size) at different heights have different effects. All of which is to say, determining whether contrails have a net warming effect or a net cooling effect on Earth’s average temperature is an outstanding scientific question.
Investigating this question requires being able to study Earth’s climate in the absence of contrails and compare average temperatures with and without. But there are always aircraft flying somewhere in the stratosphere. When planes land for the night in America, they are just taking off in the Far East and Australia, and when they stop flying there, European planes take off, and so it goes —it’s a 24/7 global operation. There are more than a million people in the air at any given moment. The only time this was not true in recent memory was after the terrorist attack on the Twin Towers in New York. All planes were grounded in the United States for three days after September 11, 2001. The measurements from 4000 meteorological stations across the United States showed that on 9/11 the difference between daytime and nighttime temperatures was, on average, 1.8ºF higher than usual. This, of course, is just one study and at one time of year, autumn. It’s quite possible that in winter, spring, and summer, when cloud coverage and the localized climate would be different, the net effect of contrails would be to decrease temperatures, not increase them. There’s a lot of ongoing work in this area, but it will never be an easy matter to resolve; our climate is complex.Certainly, it’s hard to imagine a time when we’ll be able to collect more data from a complete no-fly scenario, given that flying is such an important part of global culture. Nevertheless, scientists have widely discussed the possibility of controlling global temperatures through seeding clouds, and whether that would have the potential to avert some of the effects of climate change. Many suspect that they could manage solar radiation by increasing the reflectivity of the atmosphere by making clouds whiter.
The deliberate manufacture of contrails seems like an obvious way of testing that theory, and although such experiments are highly controversial, there are some who think they’re already being carried out in secret. Contrail conspiracy theorists argue that some contrails stay in the sky for too long, and that the only way that could be happening is if they’re being created by aerosols and other chemicals. Some of the conspiracy theorists go further still and argue that the contrails are evidence that governments have been spraying liquids across their territories, with the aim of psychologically manipulating the population through chemical means.These conspiracies play off legitimate fears that we could be manipulated and poisoned through the water we drink. The danger is real; the water supply has historically been responsible for the mass poisoning of whole communities. It still goes on in modern times; for instance, as recently as 2014, the entire city of Flint, Michigan, was poisoned by lead in the water due to government incompetence. The outbreak of cholera in Yemen, which began in 2016 and is now nearing one million cases, was caused by the breakdown of a clean water supply.
Not surprisingly, the fear of mass infection and poisoning has been a common motif in fiction, perhaps most famously in the film Dr. Strangelove, in which General Jack D. Ripper identifies the fluoridation of water as a Communist plot to undermine the American way of life: “I can no longer sit by and allow the international Communist conspiracy to sap and impurify all of our precious bodily fluids,” says General Ripper, before initiating a nuclear attack on the USSR. This movie, perhaps the greatest film to examine the circumstances under which a nation might initiate nuclear war, is right to identify the adulteration of water as a potential motive for global conflict. We all need clean water to drink—we cannot live without it —and if our water is adulterated or contaminated, it will bring about death and disease on an epic scale. The pandemics of cholera in the 19th century killed tens of millions of people before anyone understood that the disease was brought on by waterborne bacteria. And as with all liquids, water is very hard to control. It goes everywhere, eventually, moving from lakes to rivers to oceans and up into the skies. Thus the fear of water contamination is as great today as ever, and yet the water coming down from the clouds, the origin of most of the water we drink, is equally difficult to protect.Clouds know no territorial boundaries; one nation’s experiments, disasters, or actions can and do affect the rest of the world in the most intimate way.
Dr. Strangelove was made as a satire, but the suspicion and fear surrounding the potential contamination of what we put into our bodies are real and will probably never go away. “Foreign substances introduced into our precious bodily fluids without the knowledge of the individual, certainly without any choice, that’s the way your hardcore Commie works,” says General Jack D. Ripper. But replace “Commie” with “federal government,” or “capitalist corporation,” or “scientist,” or even “environmentalist,” and you have the essence of most arguments against any number of policies concerning vaccination, water chlorination, or even power generation. There are countless examples of this— just look at acid rain. Coal often contains impurities in the form of sulfates and nitrates, which become sulfur dioxide and nitrogen oxide gases when the coal is burned. These gases rise and become part of the atmosphere, and then dissolve in the liquid droplets that make up clouds. The presence of these gases makes those droplets acidic, so when they return to earth in the form of rain, they acidify the rivers and lakes and soil, killing fish and plants, and destroying forests. Acid rain also corrodes buildings, bridges, and other infrastructure, and it often does so very far away from where the original emissions—the gases from the coal —came from. It falls in a different country from where it was initially emitted, becoming a political issue as well as an environmental one. The cause of acid rain was identified during the industrial revolution in the 19th century, but it wasn’t until the 1980s that the West, the main producer of acid rain, made a concerted effort to combat it.
The nuclear disaster at Chernobyl in Ukraine in 1984 caused another pan-national problem carried by clouds. When it became clear that the radioactive elements from the explosion at the power station had become airborne, everyone knew that the prevailing winds would determine which countries would be affected. The UK was one of those countries, with sheep farmers in England and Wales suffering from radioactive rain falling on their land, becoming a part of the soil and grasses. If swift preventive measures had not been taken to stop sheep from eating this grass, they would have become radioactive too. It was only in 2012, 26 years after the Chernobyl explosion, that restrictions were finally lifted by the UK Food Standards Agency on sheep being raised in the affected regions. The world is a connected place. It’s connected through the clouds and the rain showers they produce, and in another sense, it’s connected through airplane travel.