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In a traditional greenhouse, sunlight shines through the glass causing heat to get trapped, warming up the structure. Earth’s atmosphere works similarly and this so-called greenhouse effect is necessary to maintain life. However, in the last 200 years, human activity has accelerated this natural process by pumping massive amounts of greenhouse gases into the atmosphere, resulting in a warming planet. Here is a quick look at the science behind the Greenhouse Effect.
Light is a form of energy that travels in waves, making up the electromagnetic spectrum. The light that reaches the Earth from the Sun is called solar radiation. Radiation is just a fancy way of saying transferring heat from one thing to another. Solar radiation reaches Earth mainly in the form of visible light (see figure below). Some of this light is reflected back into space by Earth’s atmosphere and surface, but most of it is absorbed by Earth’s surface. The surface heats up as a result of the energy input and then re-emits some of the energy back into the atmosphere.
Since Earth is much cooler than the sun, and wavelength is inversely proportional to temperature, Earth projects this energy back into the atmosphere at a much longer wavelength in the form of infrared radiation. It is also important to note that speed is equal to the product of wavelength and frequency. All light travels at the same speed (the speed of light or 299 792 458 m / s), so as the wavelength of light increases the frequency must decrease for the speed to remain the same.
Now without Earth’s atmosphere and the gases that compose it, all of the heat emitted by Earth’s surface would just be reflected back into space, and Earth would end up cold and uninhabitable. This is where greenhouse gases come in. These gases absorb some of the infrared rays reflected by the Earth and re-emit them back to Earth’s surface. This is called the Greenhouse Effect, a crucial process that regulates Earth’s temperature so that it can sustain life. In fact, without the greenhouse effect, Earth’s surface temperature would plummet by about 33°C.
To understand how greenhouse gases trap heat, it is important to know that light can be described as a wave, which means that different types of light have specific frequencies, or the number of waves that pass a certain point in a specific period of time.
Earth’s atmosphere comprises about 78% nitrogen, 21% oxygen, 0.9% argon with trace amounts of other gases making up the remaining 0.1%. Carbon dioxide, water vapor, and methane are the most prominent greenhouse gases in Earth's atmosphere. But why do these gases trap heat while others don’t?
Let’s first compare the molecular structures of nitrogen gas and carbon dioxide.
Oxygen and nitrogen are diatomic molecules, meaning they only have two atoms. However, if we examine a greenhouse gas like carbon dioxide, we can see that there are 3 atoms composing the molecule. Intermolecular forces cause temporary changes in the distribution of electrons in a molecule, which causes the molecules to vibrate. When oxygen and nitrogen vibrate they stay symmetrical because there are only two atoms. They simply can move further apart or closer together. This prevents them from being able to absorb infrared radiation.
But, when a greenhouse gas like carbon dioxide vibrates, the symmetry is disrupted, as the carbon atom may become closer to either of the oxygen molecules. The asymmetry that results creates something called a dipole moment. Symmetrical molecules like oxygen and nitrogen gas do not get lopsided when they vibrate so they do not have dipole moments, making them transparent to infrared radiation.
Through a process called resonance, when the frequency of a light wave matches the vibration frequency of a molecule, the molecule can absorb the energy, which is then re-emitted towards the Earth’s surface, trapping heat. So, through the concept of resonance, we can understand that carbon dioxide, water vapor, and methane all trap infrared rays because they vibrate at the same frequency that infrared light travels. The reason that solar radiation can pass through these gases on the way to Earth is that visible light travels at a much higher frequency than infrared radiation, so the molecules do not vibrate at the same frequency as the solar radiation, which can subsequently pass through Earth’s atmosphere instead of being reflected out into space.
We know that greenhouse gases are necessary to maintain life on Earth, so why are we so concerned about them? Before humans, the primary source of carbon dioxide in the atmosphere was volcanos. Volcanos basically burn fossil fuels, releasing them into the atmosphere in a volcanic eruption. However, humans have sped up this process by extracting fossil fuel from the oceans and land to use for energy and other products like plastic. As we release more carbon dioxide and methane, primary byproducts of fossil fuel combustion, more molecules in Earth’s atmosphere can absorb infrared red rays, increasing the greenhouse warming effect.
As the average temperature continues to increase, oceans will rise, ice sheets will melt, and climates will change, all of which are detrimental to life on Earth. Even scarier, as the Earth continues to warm it creates feedback loops, which accelerate warming even more. It is therefore critical that we take steps to drastically decrease our greenhouse gas emissions.
Here at Aclymate, we want to empower small and medium-sized businesses to become leaders of decarbonization. If you want to learn more about how your business can be a part of the climate revolution go to our website. You also learn more about your carbon footprint with our free carbon calculator quiz!