Climate Change For Dummies. Elizabeth May
as an odorless, colorless gas, it can also exist in solid form (think dry ice) and, when kept under pressure, in liquid form (the bubbles you see in champagne or a can of soda are carbon dioxide escaping after you uncork the bottle or open the can and remove the pressure).
When trees take up carbon through photosynthesis, they’re called carbon sinks. Plants aren’t the only carbon sinks, however. Figure 2-2 shows how the ocean, plants, and soil all act as carbon sinks, removing carbon from the atmosphere. They also store, or sequester, carbon, and they store the carbon in a carbon reservoir. For example, the ocean holds about 38,000 billion metric tons of carbon in its reservoir.
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FIGURE 2-2: The carbon cycle.
The next sections explain how everything is connected. What goes on in the atmosphere isn’t isolated from everything else in the world. It’s like that old spiritual: “Dem bones, dem bones, dem dry bones. Toe bone connected to the foot bone. Foot bone connected to the heel bone. Heel bone connected to the ankle bone. Ankle bone connected to the leg bone …” and on and on. Earth is like that too. Everything is connected. The ocean is connected to the atmosphere. The plant life — forests on land and green things under water — are all connected. Changes in the atmosphere have impacts on the oceans, the forests, the clouds, and the soil. And vice versa.
Under the deep blue sea
The ocean is the biggest carbon sink on Earth. So far, it has tucked away about 90 percent of all the carbon dioxide in the world. If that gas was in the atmosphere, not underwater, the world would be a lot hotter.
The exchange of carbon dioxide between the ocean and the air happens at the surface of the water. When air mixes with the surface of the ocean, the ocean absorbs carbon dioxide because carbon dioxide is soluble in water (that is, carbon dioxide can be absorbed by water). And, in fact, the seas’ ability to absorb carbon dioxide is referred to as the solubility pump because it functions like a pump, drawing carbon dioxide out of the air and storing it in the ocean.
The ocean also acts as a biological pump to remove carbon dioxide from the atmosphere. Plants close to the surface of the ocean take in carbon dioxide from the air and give off oxygen, just like plants on land. (We discuss this process, known as photosynthesis, and the role that plants play in the carbon cycle in the following section.) Phytoplankton are microscopic plants that live in water. You may know them as algae, most commonly seen as the greenish clumpy plants that float around on ponds and other water. Phytoplankton have short but useful lives. If other organisms don’t eat them, they simply die within just a few days. They then sink to the ocean floor, mix into the sediment, and decay. The carbon dioxide that these plants absorb during their brief lives is well and truly sequestered after their little plant bodies are buried.
Each year, the oceans put away about another 2 billion metric tons of carbon dioxide. Figure 2-3 demonstrates how the ocean interacts within the carbon cycle. According to the World Economic Forum, recent research suggests that the 2 billion metric tons of carbon a year may actually be an underestimate. It could be as much as .9 billion metric tons more — every single year. Sometimes it’s expressed as ten Hiroshima-size nuclear bombs worth of energy in heating — absorbed by the oceans per second. Scientists writing about the huge amount of energy stored by the oceans search of explanations in equivalents that people can grasp — like nuclear bombs. That’s because the science is expressed in unfamiliar terms. Describing the energy in terms of nuclear bombs is a scientist’s way of expressing that the ocean absorbed 20 sextillion joules of heat in 2020.
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FIGURE 2-3: The relationship between carbon dioxide and the oceans.
Why people couldn’t survive without plants
You may not have realized back in elementary school that when you were reading about photosynthesis, you were actually getting the basics of modern climate science. (Photosynthesis occurs when plants take in energy from the sun and carbon dioxide from the atmosphere and turn it into oxygen and sugars.) Figure 2-4 may jog your memory.
Trees are the planet’s biggest and most widespread plants, and the forests are wonderful carbon sinks.
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FIGURE 2-4: The process of photosynthesis.
Mangrove forests are another little appreciated forest ecosystem. They’re also tropical, but they’re rooted in water. Research shows they may actually be four times more effective in sucking up carbon than tropical forests on land. But they’re at risk. About a third of the world’s mangroves have been removed — mostly for tourism developments to create beaches and for farming shrimp in toxic shrimp ponds. Planting mangroves helps nature, creates homes for fish, protects coastal communities from big storms, and fights climate change. And unlike the forests on land, they can’t burn up because they live in water.
Forests in Canada, the United States, and Russia aren’t as effective at soaking up carbon because they take a rest in the winter but are still very important in the planet’s carbon balance. The northern forests make up for the reality of their seasonal work, through the relatively richer and deeper soils. Northern forests store more carbon in carbon reservoirs, even though tropical forests take up more carbon on an annual basis.
Grasslands also play an important role
About 40 percent of the Earth’s surface is grassland, mostly used for grazing animals. They aren’t only cattle — sheep, goats, yaks, camels, llamas and alpacas, and the people who tend to them all depend on grasslands. Grasslands are one of the most effective carbon sinks — the deep roots of grasses can store as much carbon as trees, and that carbon remains even when the grasses are grazed or burned off. Grasslands are rapidly being depleted by conversion to more intensive agriculture. But climate scientists now see their enormous value in the fight against global warming.
Down to earth
Soil also stores carbon. Plants draw in carbon dioxide and break it down into carbon, breathing the leftover oxygen into the atmosphere. The carbon makes its way into the soil through the plants’ root systems or when the plant dies. See Figure 2-5 for a diagram showing how soil and trees exchange carbon dioxide with the air.