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Global Warming vs Greenhouse Effect

Updated on September 21, 2012

Global warming has become a highly politicized topic not just in the United States but around the world. Debates about global warming from the Internet to the floor of Congress rarely have much to do with actual science, but instead hinge on wild conspiracy theories involving leaked emails, UN sustainability proposals, and Al Gore's power bills.

However, at the heart of all this debate and denialism are some very basic principles of physics and chemistry commonly known as the greenhouse effect. While climate is extremely complicated and is controlled by a great many factors, the greenhouse effect plays a critical role in regulating the climate - as well as making our planet habitable.

The Greenhouse Effect Illustrated -click to enlarge
The Greenhouse Effect Illustrated -click to enlarge | Source

Want A More Technical Explanation?

The Greenhouse Effect Explained

We often think of the Earth as being in the habitable zone of the Sun - a comfortable distance at which water can remain in a liquid state. However, liquid water is only possible on Earth due to the greenhouse effects of the atmosphere.

If the Earth had no atmosphere, its temperature would be a chilly -0.4° Fahrenheit (-18° Celsius). The molecules in the blanket of air surrounding our planet absorb radiation of certain incoming wavelengths, reflect others, and allow still other wavelengths to pass through. Most of the radiation from the Sun comes in the form of ultraviolet and visible light, with lesser amounts in the infrared and other portions of the spectrum. Ozone and oxygen high in the atmosphere block much of the ultraviolet radiation from reaching the ground. Visible light mostly passes through, with some scattering in the lower wavelengths, toward the blue end of the spectrum (making the sky blue). Infrared light mostly passes through the atmosphere, warming the surface.

The Earth then emits thermal radiation in the near-infrared part of the spectrum. Greenhouse gases such as H2O (water vapor), CO2 (carbon dioxide), CH4 (methane), and O3 (ozone) absorb this thermal radiation and then re-radiate it in different directions, sometimes out into space and sometimes back down to the ground. It is the portion that is re-radiated to the ground that creates the greenhouse effect, and keeps our planet at a temperature suitable for liquid water and for life.

When atmospheric levels of greenhouse gases remain steady, the planet stays in a state of equilibrium between incoming and outgoing energy. When the concentration of greenhouse gases in the atmosphere changes, however, it can lead to a runaway greenhouse effect, in which positive feedback mechanisms throw this equilibrium off-balance.

Fossilized leaf chewed by insects during the Paleocene-Eocene Thermal Maximum
Fossilized leaf chewed by insects during the Paleocene-Eocene Thermal Maximum | Source

Runaway Greenhouse Effect: The Paleocene–Eocene Thermal Maximum

Geologic history provides us with a good example of a runaway greenhouse effect in the Paleocene-Eocene Thermal Maximum (PETM), a period of rapid warming (on a geologic time scale) that occurred around 55 million years ago. Average global temperatures rose by 6° Celsius (10.8° F) over a 20,000 year period, eventually cooling to normal temperatures after 150,000-200,000 years.

Paleobiologists have been able to reconstruct the climate of this period by studying sediment deposits and the fossilized shells of marine organisms. These retain a chemical signature from the seawater around them, which in turn tells researchers about ocean temperatures at the time. During the PETM, ocean temperatures rose drastically, from a 4 degree sea surface temperature rise near the equator to an 8 degree rise in the deep ocean at higher latitudes.

The consequences of this sudden temperature increase were a change in ocean currents, rise in sea levels, a shift in precipitation patterns, and acidification of the oceans. The effects on life at the time were mixed. There was a mass extinction of 35-50% of deep-sea plankton during this period, and extinction of a number of small mammal and coastal plant species. On the other hand, there was a great diversification of other mammals at the time, and the orders leading to modern-day cattle, horses, deer, and primates appear in the fossil record at this time. This was also a period of migration, as temperate-zone plant species are found at much higher latitudes than before, and fossils of tropical fish are found in the Arctic.

The exact cause of the PETM is still a mystery to paleogeologists, but the evidence points to a massive release of carbon as a triggering event. This then led to a positive feedback loop as warming temperatures caused more carbon dioxide and other greenhouse gases to be released into the atmosphere, intensifying the warming even further. When the planet finally cooled to a stable equilibrium temperature 200,000 years later, it was a very different place.

Global Warming: More Than Just Temperature Change

The Paleocene-Eocene Thermal Maximum saw a raise in temperatures of 6 degrees Celsius over about 20,000 years. Current worst-case climate models show our planet undergoing a similar average temperature rise by the end of this century due to the increased concentration of carbon dioxide and other greenhouse gases in the atmosphere since the Industrial Revolution.

While some species did show remarkable adaptability during the geologically rapid thaw of the PETM, we cannot expect to see this during the geologically-instantaneous warming of the current era. The consequences for the biosphere will be drastic, and we should expect to see far more extinctions and disruptions to the precipitation patterns we rely on for growing crops and raising livestock.

Though climatologists may disagree over some of the details of how the climate will change due to the introduction of an extra 117 ppm of CO2 into the atmosphere, basic physics and chemistry demonstrate that this will intensify the Earth's greenhouse effect and warm the planet. This basic fact is beyond dispute. How we as a species will work to solve this climate crisis and mitigate its consequences, on the other hand, is still an open question.


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    • profile image

      Howard Schneider 5 years ago from Parsippany, New Jersey

      Thank you very much for clearly explaining this, Scott. This problem is huge threat to us and I wish we were taking faster and more concrete action to stop this.

    • scottcgruber profile image

      scottcgruber 5 years ago from USA

      I'll check it out, thanks for the tip.

    • Robert Kernodle profile image

      Robert Kernodle 5 years ago

      Hi Scott,

      I most certainly am not (even figuratively) arguing that 2 + 2 = 5. I am, in fact, arguing to the contrary -- that things are NOT so simple.

      A number of very qualified, mathematically trained people have argued IN FAVOR of (or along similar lines as) Gerlich and Tscheuschner.

      One blog does NOT refute these guys. They have answered their critics convincingly, as I stated in my hub on this topic.

      You might be interested in Robert Wood's 1909 experiment that directly disproves the back-radiation cornerstone idea of the CO2 greenhousse theory. And others have duplicated Wood's findings.

    • cclitgirl profile image

      Cynthia Calhoun 5 years ago from Western NC

      Great, informative article. I definitely enjoyed the read. :) Thank you for sharing this and I wish I could make a time-travel machine just to see what earth will be like in 150-200 years. :) I wonder if our species will figure out a way to mitigate this problem.

    • Melis Ann profile image

      Melis Ann 5 years ago from Mom On A Health Hunt

      Great explanation of a topic that confuses many people. The scary thing is that our habits won't change fast enough to stop what is already put into motion. Voted up and SHARED.

    • Teresa Coppens profile image

      Teresa Coppens 5 years ago from Ontario, Canada

      Excellent article Scott. Very well researched and presented. Energy from the sun makes the world go round so to speak, including the oceans. We all know what we're doing to exacerbate the problem. We have to be willing to take those steps required which for most is easier said than done! Voted up!

    • somethgblue profile image

      somethgblue 5 years ago from Shelbyville, Tennessee

      Check this hub out as it relates to yours in some ways

    • somethgblue profile image

      somethgblue 5 years ago from Shelbyville, Tennessee

      This is quite possible the most important sentence in the article . . . During the PETM, ocean temperatures rose drastically, from a 4 degree sea surface temperature rise near the equator to an 8 degree rise in the deep ocean at higher latitudes.

      I have been saying all along that we should look at the real reasons the Ocean temperatures are rising.

      It is estimated that over 3.5 million fissures, cracks and openings in the Earth's Mantle are on the Ocean floors allowing the rising core temperature of this planet to create more CO2 in our Oceans which creates more CO2 in our atmosphere, hence Global Warming!

      I like the word Denialist . . . permission to steal it?

    • scottcgruber profile image

      scottcgruber 5 years ago from USA


      You can debate the fact that 2+2=4 if you like. If you Google the phrase "2+2=5," you get 2.23 billion results.

      By your logic, this means that 5 is a legitimate answer to the 2+2 problem that challenges the arithmetical orthodoxy, and should be considered equally as valid as 4.

      The only flawed argument is Gerlich and Tscheuschner's:

    • Robert Kernodle profile image

      Robert Kernodle 5 years ago

      Here's my take:

      Others question the orthodox view too:

      Again, I ask, if both sides of the debate can produce such convincing arguments, then is either side really right or really wrong?

      Maybe the general argument is somehow flawed.