Climate Change For Dummies. Elizabeth May
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Название: Climate Change For Dummies
Автор: Elizabeth May
Издательство: John Wiley & Sons Limited
Жанр: Биология
isbn: 9781119703129
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The solar cycles do affect climate in the short term, but the U.S. National Oceanic and Atmospheric Administration (NOAA) reports that the impact from the light intensity of the sun versus the impact from GHG emissions is a ratio of approximately 9 to 40. So, GHGs have more than four times the effect of solar cycles.
Other cycles that concern the sun are the Milankovitch cycles. Although they sound like Mr. Milankovitch’s bike collection, Milankovitch cycles are actually natural cycles of the Earth — one of these cycles, for example, is the way in which the planet tilts toward or away from the sun. These cycles may explain the glacial cycles — the ins and outs of ice ages. (We talk about the Milankovitch cycles in more detail in the section “Making the Case for Carbon,” later in this chapter.)
Although they’re important, the Milankovitch cycles have minimal effect on climate in comparison to the effects from GHG emissions when you look at them in terms of relatively short timescales — from decades to centuries. Overall, the IPCC says that the sun likely has little to do with global average temperature rises since 1950. In fact, computer models suggest that the Earth would be cooling if not for increases in GHGs.
Cloud cover
Scientists have known for a long time that climate affects rainfall. NASA (the National Aeronautics and Space Administration in the United States) has shown that the relationship may work in reverse, however — that the changing rain patterns might, in turn, indirectly affect global warming. Rainfall patterns correspond to cloud cover. Depending on their thickness and shape, clouds can reflect light during the day and hold in surface heat overnight (see Figure 3-1). The amount of water vapor in the air has continued to increase (which we talk about in Chapter 2), which means more clouds, which means more rainfall. Perhaps this increase in cloud cover can explain why nighttime temperatures are rising more than daytime temperatures in global warming trends. It gives a whole new meaning to having a hot night!
Ultimately, however, increased cloud cover seems to be a result, not a cause, of climate change. But, like the increased water vapor, it may further contribute to global warming.
© John Wiley & Sons, Inc.
FIGURE 3-1: Clouds reflect light during the day and hold in surface heat overnight.
Long-term climate trends
Over the course of many millions of years, the Earth’s temperature has varied widely. Scientists know that the most recent period of ice ages started about 2 million years ago, and since 800,000 years ago, the planet started into a cycle of an ice age every 100,000 years or so. Currently, the Earth is in an interglacial period — meaning the weather is warm and stable enough that humans can develop and expand societies. Human civilization started at the beginning of this interglacial period about 10,000 years ago. Given that past warm interglacial periods lasted about 10,000 years, on average, scientists would expect the world to be getting cooler, not warmer. In fact, it appears that this cooling was happening between the middle ages and the 19th century (the little ice age), but then came the Industrial Revolution.
EL NIÑO: GLOBAL WARMING CAUSE, EFFECT, OR BOTH?
El Niño is a natural weather cycle that has the power to change global temperatures. It’s been around for hundreds — possibly millions — of years. El Niño involves the tropical Pacific Ocean warming by 0.9 degrees F (0.5 degrees C) or more for about three months at a time. This warmed water eventually loses that heat to the atmosphere, causing the average air temperature (at the surface, or where humanity lives in the lower part of the atmosphere) to go up a few months later, which then alters the overall climate temporarily. The temperature of the ocean then settles back down to normal and returns to its regular cycle of ups and downs.
Scientists don’t yet know whether global warming is affecting these cycles, but global warming and El Niño cycles are very interrelated. Part of the reason scientists can’t distinguish between the impacts of global warming and El Niño on climate is because they’re so linked and because they both influence many different aspects of regional climate that they can actually change one another. A computer model giving future scenarios of climate that includes both El Niño and global warming doesn’t yet exist because of the difficulty that exists between identifying the separations between the two.
Some models say El Niño will become stronger, but others say it’ll weaken. Evidence suggests that El Niño cycles have been stronger and happening more often over the past few decades, and climate models project that climate change will cause sea-surface temperatures to rise in the tropical Pacific Ocean — similar to El Niño conditions. Scientists are working constantly to advance their understanding of the relationship between climate change and El Niño.
Two unknown questions remain: How much temperature rise is the result of El Niño and how much is the result of global warming? Are El Niño temperatures any higher because of global warming?
Making the Case for Carbon
Scientists have collected evidence that confirms the buildup of carbon dioxide in the Earth’s atmosphere as by far the most likely cause of the current climate crisis. And they’ve built computer models to forecast future effects.
Geologic and prehistoric evidence
They can measure exactly how much carbon dioxide has been in the Earth’s atmosphere historically. Climatologists (scientists specializing in climate science) have drilled deep — as deep as 2 miles (3 kilometers) — into ancient ice in places such as Antarctica and Greenland. They’ve pulled up ice cores — long, thin samples of many layers of ice that has been packed down over thousands of years, which look like really (really) long pool noodles. (Figure 3-2 shows two scientists drilling for an ice core sample.) When the layers are clearly visible, the ice core looks like a pool noodle with horizontal stripes.
National Oceanic and Atmospheric Administration
FIGURE 3-2: Drilling for an ice core sample.
Scientists can date an ice core by counting the layers of ice — just like you can tell the age of a tree by counting its rings. The layers of ice tell them exactly when the ice was formed. Each layer of ice includes little pockets of trapped air. These frozen air bubbles are like time capsules of the ancient atmosphere. They’re full of gas, including carbon dioxide, that has been trapped for hundreds of thousands of years. СКАЧАТЬ