![]() “Molecules with just two atoms, like oxygen (O 2) and nitrogen (N 2), really can’t wiggle much,” he says. He describes CO 2 molecules as being able to “flap their wings” a little bit. Mark Potosnak is an Earth scientist at DePaul University in Chicago, Ill. (The CO 2 molecule is also nonpolar, which means that all of the electric charges inside it are spread out relatively evenly.) This means that the carbon shares two pairs of electrons - four electrons in all - with each of the oxygen atoms. One reason it forms this straight-line shape is its two double covalent (Koh-VAY-lunt) bonds. If you could zoom in to see a single molecule of CO 2, it would look like a straight line with a carbon atom in the center and oxygen atoms at either end. Science Photo Library/Science Photo Library/Getty Images The gray attachments show the double bonds that give this molecule its straight-line structure. CO 2 is typically measured in parts per million because it is 1,000 times more prevalent than the other gases, but is shown as parts per billion in the table for consistency.This illustration of a molecule of carbon dioxide shows a central carbon atom (black) linked to oxygen atoms (red) at either end. Some gases (like CO 2) are made by both natural and manmade processes, while others (like hydrofluorocarbons) are only the result of human industrial activity. The table below shows the relative concentrations of these major greenhouse gases and their sources. Some carbon dioxide will be absorbed very quickly, while some will remain in the atmosphere for thousands of years. * No single lifetime can be given for carbon dioxide because it moves throughout the earth system at differing rates. Global Warming Potential and Atmospheric Lifetime for Major Greenhouse Gases Carbon Dioxide Global Warming Potential, 100-year time horizon Likewise, methane is responsible for a large portion of recent warming despite having a GWP much lower than several other greenhouse gases because emissions have increased drastically.įifth Assessment Report (Intergovernmental Panel on Climate Change, 2014). These values are periodically updated by the scientific community as new research refines estimates of radiative properties and atmospheric removal mechanisms (sinks) for each gas.ĭespite carbon dioxide’s comparatively low GWP among major greenhouse gases, the large human-caused increase in its atmospheric concentration has caused the majority of global warming. The table below presents atmospheric lifetime and GWP values for major greenhouse gases from the Fifth IPCC Assessment Report (AR5) released in 2014. ![]() A gas with a long lifetime, but relatively low radiative efficiency, may end up exerting more warming influence than a gas that leaves the atmosphere faster than the time window of interest but has a comparatively high radiative efficiency, and this would be reflected in a higher GWP. Gases with high GWPs will warm the Earth more than an equal amount of CO 2 over the same time period. This is often calculated over 100 years, though it can be done for any time period. the strength of their greenhouse effect) of each unit of gas (by weight) over a specified period of time, expressed relative to the radiative effect of carbon dioxide (CO 2). ![]() These characteristics are incorporated in the Global Warming Potential (GWP), a measure of the radiative effect (i.e. The second is the atmospheric lifetime, which measures how long the gas stays in the atmosphere before natural processes (e.g., chemical reactions) remove it. ![]() The first is their ability to absorb energy and radiate it (their “radiative efficiency”). Two characteristics of atmospheric gases determine the strength of their greenhouse effect. Small changes in the atmospheric concentration of these gases can lead to changes in temperature that make the difference between ice ages when mastodons roamed the Earth, and the sweltering heat in which the dinosaurs lived. Multiple gases contribute to the greenhouse effect that sets Earth’s temperature over geologic time. ![]()
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