Climate Change For Dummies. Elizabeth May
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gases in the atmosphere trap the sun’s heat in a similar way. These particular gases are called greenhouse gases because they cause this greenhouse effect. The Earth is bombarded by radiation from the sun. Some of this radiation can be seen (think visible light), and some of it can’t be (ultraviolet light, for example).
A portion of this radiation, about 30 percent on average, bounces off clouds, ice, snow, deserts, and other bright surfaces, which reflect the sun’s rays back into outer space. The other 70 percent is absorbed by land or water, which then heats up. And the Earth emits some of that heat — in the form of infrared radiation (electromagnetic waves most commonly known as heat). The unique qualities of the GHGs come into play: The GHGs absorb some of the escaping infrared radiation in the lower atmosphere, and re-radiate part of that back down. So, less of the radiation from the Earth’s surface gets to outer space than it would have without those gases, and that energy remains in the atmosphere and returns to the Earth’s surface — making both the atmosphere and Earth itself warmer than they would be otherwise.
To see the greenhouse effect in action, look at Figure 2-1.
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FIGURE 2-1: The greenhouse effect in action.
If the planet had no atmosphere or GHGs, humanity would be left out in the cold. The Earth wouldn’t be able to keep any of the heat that it gets from sun. Thanks to GHGs, humanity is kept reasonably warm, enjoying an average temperature of 59 degrees Fahrenheit (15 degrees Celsius), some 62.6 to 64.4 degrees Fahrenheit (17 to 18 degrees Celsius) warmer than without GHGs.
Too much GHG turns the heat up beyond that to which societies and ecosystems have become adjusted. The atmosphere on the planet Venus is 96 percent carbon dioxide (the key GHG that we talk about in the following section). Because of Venus’s concentration of GHGs and its relatively close proximity to the sun, it’s extremely hot — surface temperatures of up to 500 degrees Celsius. Meanwhile, the atmosphere on Mars has 95 percent carbon dioxide, but it’s very thin, and the planet’s position is farther away from the sun than Earth, so it’s extremely cold — a chilly –80 degrees Fahrenheit (–60 degrees Celsius).
Focusing On Carbon Dioxide: Leader of the Pack
Earth’s atmosphere contains 24 different GHGs, but just one of them accounts for the overwhelming majority of the effect: carbon dioxide (or CO2, for short). This gas accounts for about 63 percent of the GHG warming effect in the long run. (In the short term, over the last 5 years, it has accounted for 91 percent. See Table 2-1 for more on the intensity of gases over time.) If you’re itching to know about the other 37 percent of greenhouse warming, check out the section “Checking Out the Other GHGs,” later in this chapter.
Given the important role that carbon dioxide plays in warming the Earth, you may be surprised by how little of it is in the atmosphere.
Nitrogen: 78 percent
Oxygen: 21 percent
Argon: 0.95 percent
Carbon dioxide, by contrast, currently makes up only 0.0412 percent of all the air in the atmosphere. Human activities have helped increase that concentration from pre-industrial times, when it was about 0.0280 percent.
When scientists talk about air quality and the chemistry of the atmosphere, they often use the term parts per million (ppm). So, currently out of every million parts of air, only 412 are carbon dioxide. That’s not much carbon dioxide, but what a difference it makes! Until recent changes in atmospheric chemistry caused by human activity, for around the last million years, carbon dioxide concentrations never exceeded 285 ppm. It’s like the hot pepper you put into a pot of chili — just right is just right, but if you have just a little too much, watch out.
The next sections explain the carbon cycle. If not for humans digging up the fossilized stored carbon of millennia ago — called fossil fuels — the Earth’s carbon cycle would have remained in balance. However, now the carbon cycle is out of balance. And that’s a key reason the weather and climate are no longer so hospitable.
Looking at the carbon cycle
Carbon dioxide occurs naturally — in fact, you, and every animal and insect on Earth that breathes in air, produce carbon dioxide every time you exhale. You inhale oxygen (and other gases), which your body uses as a nutrient, and you breathe out what your body doesn’t need, including carbon dioxide. You aren’t alone in using this process. But other organisms, mostly plants, suck carbon dioxide out of the air. Trees and grasses, for example, take in carbon dioxide and give out oxygen — the complete opposite of what people do.
The carbon cycle is the natural system that, ideally, creates a balance between carbon emitters (such as humans) and carbon absorbers (such as trees), so the atmosphere doesn’t contain an increasing amount of carbon dioxide. It’s a huge process that involves oceans, land, and air. Life as humans know it — from microscopic bugs in the oceans to you and me, and every fern and plant in between — would disappear without this cycle. You can think of the carbon cycle almost as the Earth breathing in and out.
A RECIPE THAT GIVES YOU GAS
Carbon dioxide is composed