We often hear the term ‘greenhouse effect’ in the negative context of global warming – the melting of the world’s glaciers and dangerous changes in climate. But the greenhouse effect is actually not something terrible in itself, rather it is a very important and positive part of maintaining the Earth’s energy balance.
Because of the greenhouse effect, Earth can stay warm enough for life to survive. If the greenhouse effect did not exist on Earth, our planet would probably become similar to Mars. The Martian atmosphere is not dense enough, so heat cannot be returned to the planet. So it’s very cold there.
So, what exactly is the greenhouse effect?
Basics Of The Greenhouse Effect
The name of the process comes from greenhouse. The greenhouse effect is the same process that keeps the Earth warm enough to support life, just as a greenhouse keeps its environment warm enough for plants to grow.
An example of the greenhouse effect that we experience in everyday life is the heating of the interior of a car due to prolonged exposure to the sun.
You must have noticed that when the car is in the sun for a long time, its interior feels much hotter than the outside temperature. Sunlight enters through the car window. Some of the sunlight’s heat is absorbed by car seats, dashboards, carpets and mats.
When these objects begin to emit heat, not all of the heat escapes through the window. Some of it is reflected back in, or returned. The wavelengths of heat emitted from car seats, dashboards, carpets or mats are different from the wavelengths of sunlight entering through windows. Because of this, when heat is released from these objects, not all of the heat can escape from inside the vehicle. Window glass does not allow much of this different wavelength of heat to escape.
As a result, less energy is coming out of the car than is going into it. As a result, the heat inside the car increases continuously.
Using this example of a car in the sun, we can also think of Earth’s atmosphere as a giant, spherical car window. The greenhouse effect is exactly how the Earth warms more than its surroundings.
About Earth’s Natural Greenhouse Effect
When sunlight hits Earth’s atmosphere and surface, about 70% of the energy stays on the planet by being absorbed by its land, oceans, vegetation, and other elements. The remaining 30% is reflected back into space by clouds, snow fields, and other reflective surfaces.
But the 70% of energy that enters the earth, does not remain in the earth forever (otherwise the earth would have turned into a burning fireball). Like car seats and dashboards for example, objects around the Earth that absorb the sun’s heat sometimes radiate or emit a portion of it at a different wavelength.
This absorption-radiation process keeps the Earth in radiative equilibrium: heat from the Sun is constantly hitting the Earth, warming it; A warmer Earth then radiates some of that heat back into space, cooling itself. The more the Earth absorbs solar heat, the more heat it emits.
Some of the heat emitted by the Earth reaches space. The rest is trapped in the Earth’s atmosphere as carbon dioxide, methane gas and water vapor and returns to Earth. Just as the heat from inside the car escapes, it is intercepted by the glass of the car window and returns back.
The heat that cannot escape through the Earth’s atmosphere keeps the Earth warmer than its outer environment, space, because as much energy as enters the Earth through the atmosphere cannot escape. This is the greenhouse effect, which keeps the Earth warm.
So the greenhouse effect is actually a good thing. And like most good things, the greenhouse effect is great in moderation.
But we now often associate greenhouses with environmental damage, because the greenhouse effect has been out of balance since the Industrial Revolution. Earth’s atmosphere is trapping too much heat.
Greenhouse-Making Of Mars
Some scientists have suggested that we can send some factories to Mars and repopulate the surface of Mars. These factories would release water vapor, carbon dioxide and other greenhouse gases into the Martian atmosphere. If enough greenhouse gases could be emitted, the atmosphere would thicken and Mars would begin to retain heat. The environment will become conducive to plant survival.
Once plants spread across Mars, they would begin to produce oxygen. Thanks to greenhouses, after a few hundred or thousands of years, Mars may have an environment where humans can easily walk.
Combustion Of Fossils Fuels And Enhanced Greenhouse Effect
Scientists estimate that without an atmosphere, Earth’s surface temperature would be about 54 degrees Fahrenheit (30 degrees Celsius) cooler than it is today. This would have brought the average surface temperature of the Earth to about 5 degrees Fahrenheit (minus 15 degrees Celsius). On the other hand, the surface temperature of Mars is about minus 9.4 degrees Fahrenheit (minus 23 degrees Celsius).
Which means, without the Earth’s atmosphere and the greenhouse effect, we would be in dire straits. Similarly, excess greenhouse effect can also have devastating consequences on Earth. If the atmosphere contains more heat-absorbing gases, excess radiation is trapped there. Then excess heat cannot escape from the earth. And the Earth then becomes warmer than its ideal temperature.
In fact, the Earth is not releasing enough heat to keep itself cool. What is happening as a result is what we know as “global warming”. This is essentially an uncontrolled greenhouse effect.
The main reason for this problem is the increase in the concentration of carbon dioxide gas in the atmosphere. After water vapor, carbon dioxide is the most abundant greenhouse gas.
Carbon dioxide levels on Earth are mainly kept in balance by the activity of plants. But since humans began burning carbon dioxide-emitting fossil fuels at increasing rates, this balance has been disrupted.
We are putting more carbon dioxide into the atmosphere than plants can absorb (added to that by deforestation).
Before the Industrial Revolution at the end of the eighteenth century, the concentration of carbon dioxide in the atmosphere was about 280 parts per million (ppm). In the mid-20th century, that number was 330 ppm. And in 2023, that number is at about 420 ppm!
Because of this increase in Earth’s carbon dioxide, Earth’s temperature is currently 2 degrees Fahrenheit (1 degree Celsius) warmer than pre-industrial times—which may not sound like much. But the horror is understood when you hear that scientists predict severe, irreversible global impacts of a 2°C temperature rise. These include large-scale melting of ice, sea level rise and subsequent flooding, extreme weather and severe loss of wildlife habitat.
Since the Industrial Revolution, carbon dioxide and other greenhouse gases have increased the Earth’s temperature, especially in the polar regions. As a result, glaciers are melting at a faster rate, breaking into the ocean and moving inland.
Actions have already begun to reduce global greenhouse gas emissions through agreements such as the Kyoto Protocol and the Paris Agreement. It remains to be seen whether these initiatives succeed in averting disaster, or whether we suffer the consequences of inadequate and late action.
