Climate change. One of the phrases you say if you want to needlessly cause an uproar at social gatherings, along with “immigration policy” and “GIF is pronounced with a hard ‘G’.” We’ll be mentioning climate change a lot here at The Science Distillery, so it will be worthwhile to at least discuss the basic atmospheric mechanisms involved. Keep in mind, this article will not dive into specific impacts and hot-button issues like sea level rise, melting of polar icecaps, ocean acidification, and the other “sky is falling” things that either just get people depressed, or skeptical and tuned out. We’ll save those for later articles. Additionally, it is important to note that we are staying completely nonpartisan for this and future articles on the subject. We will just be sticking to the facts. So without further ado, let’s jump right into the phenomenon known as The Greenhouse Effect. We will start by discussing the basics of atmospheric impact on a planet’s climate, followed by a comparison of Earth with other planets in our Solar System, and finishing with a more in-depth look at the science behind the Greenhouse Effect.

 

Let’s say you’re cold one night while curled up on the couch watching TV. What do you do? Throw on a blanket, of course! Your body gives off heat, and a blanket acts as an insulator to trap that heat inside. If you’re still cold, you throw on another blanket to form a thicker layer of insulation. Common sense, right? The Earth’s atmosphere acts in a similar way. It behaves as an insulator, and is a large factor in keeping our planet’s climate consistent and temperate.

 

Other Planets in our Solar System

At its greatest extremes, Earth’s surface temperature ranges from 58°C (136°F), recorded in Libya, to -88°C (-126°F), in Antarctica.

  • Compare this with Mercury, which has almost no atmosphere, and ranges in temperature from 427°C (801°F) during the day to -173°C (-279°F) at night.
  • Venus, on the other hand, has an incredibly thick atmosphere, and despite being farther from the Sun than Mercury, its average surface temperature actually exceeds Mercury’s, at about 470°C (870°F). This is hot enough to melt lead! (We will return to Venus later on).

 

The Greenhouse Effect

Put simply, the Greenhouse Effect is the phenomenon in which gases in the atmosphere trap radiation from the Sun inside the planet’s atmosphere, thus warming up the planet. This occurs because the atmosphere is transparent to shortwave radiation from the Sun, but not to longwave radiation reflected back from Earth. Let’s get these definitions out of the way first:

  • Shortwave radiation – This is high-energy radiation released from the Sun, in the form of visible light and ultraviolet rays. It is referred to as shortwave radiation because, well, it has a shorter wavelength.
  • Longwave radiation – This is lower-energy radiation released from the Earth as infrared, or heat. It is called longwave radiation because, you guessed it, it has a longer wavelength.

Basically, high energy shortwave radiation is emitted by the Sun, and due to its small wavelength, it can bypass atmospheric gases on a molecular level, thereby reaching the surface. A lot of this energy is absorbed by the Earth (ex: the ground heats up), and is re-emitted as lower energy longwave radiation, or infrared, back out into space. However, due to infrared’s longer wavelength, it cannot bypass atmospheric gas as easily, and much of it is deflected back down to Earth when it hits atmospheric compounds. As this heat is unable to escape back into space, the planet warms. Simple, right?

greenhouse effect

Figure 1: An incredibly simplistic diagram of the greenhouse effect

 

Greenhouse Gases

Now, not all gases in the Earth’s atmosphere are particularly good at trapping heat. Nitrogen (N2) and Oxygen gas (O2), for example, make up the majority of our atmospheric composition, but do not contribute to the greenhouse effect. The ones that do are called greenhouse gases, a term you are probably familiar with by now. Greenhouse gases are compounds whose molecular structures are particularly good at absorbing and re-emitting infrared rays. The most well-known greenhouse gases (GHGs) are carbon dioxide (CO2) and methane (CH4), although others include water vapor (H2O(g)), tropospheric (lower atmosphere) ozone (O3), and nitrous oxide (N2O). Greenhouse gases have always been present in trace amounts in Earth’s atmosphere, and compounds like CO2 have been critical in regulating Earth’s temperature over the eons.

It stands to reason, then, that if gases like CO2 can block heat energy from escaping Earth, then adding more of it to the atmosphere would increase the amount of heat trapped inside the Earth’s atmosphere, which would then warm the planet at a greater rate. Make sense?

Hopefully, by this point, you’re all still with us here, and haven’t completely written us off as loons peddling a crackpot narrative. If you are, then you may be asking “So what’s the big deal? Even if the planet warms a little, it can’t be that bad, can it? How bad can it get?” To which my first response would be to compliment you on asking questions, because questioning what is previously given to you as fact is one of the foundations of science. And fortunately for us, we can answer those three questions with one example – Venus.

 

The Runaway Greenhouse Effect

Earlier in this article we mentioned other planets in our solar system as examples of how the presence of an atmosphere can have a crucial role in regulating planetary temperature. We brought up Venus as a counterpoint to Mercury, and how despite Venus being further from the Sun, its surface temperatures exceed Mercury’s. Why is that the case? Because Venus’ thick atmosphere is composed almost entirely of carbon dioxide. In fact, while most of Earth’s carbon is present on the surface or underground in rocks, the majority of Venus’ carbon is present as CO2 in its atmosphere. This abundance of CO2 in Venus’ atmosphere over the ages has resulted in surface temperatures that exceed the melting point of lead. This is believed to be the result of a runaway greenhouse effect, where a positive feedback loop between levels of GHGs and heat caused Venus’ temperature to spiral out of control.

Now, are we saying that such a phenomenon can happen here on Earth? Absolutely not. In fact, the Intergovernmental Panel on Climate Change has stated that the likelihood of a similar runaway greenhouse effect occurring here on Earth due to human causes is just about zero. So don’t run around misquoting us as saying climate change will turn Earth into a Venusian hellscape. It will not. However, we are saying that the presence of carbon dioxide and other greenhouse gases is proven to have a warming effect on a planet’s climate, and even changes of a few degrees will have a dramatic impact on planetary ecosystems that are sensitive to small changes. Humans are at the top of the food chain, which means that changes that occur at the very bottom can and will have a ripple effect upwards, affecting us just as much as those sad pictures of cute animals you see on TV. But don’t take our word for it here – stay updated with our subsequent articles that will dig into more specific issues, impacts, and consequences revolving around climate change.

 

-K

 

Sources:

D.R. Feldman et al. Observational determination of surface radiative forcing by CO2 from 2000 to 2010. Nature. Published online February 25, 2015. doi: 10.1038/nature14240.

Weingroff, M. (n.d.). The Greenhouse Effect. Retrieved August 13, 2017, from https://www.ucar.edu/learn/1_3_1.htm