What is climate change?

Imagine a typical day in spring. When you wake in the morning and look from the window, the sky is cloudy and gray. A while later it begins to rain, but then, toward the middle of the morning, the sky begins to look lighter in the west. The rain eases and then stops. Patches of blue sky appear and grow larger as the gray cloud thins and dissipates. By afternoon the Sun is shining and the air feels warm. There is a short, light shower in the early evening, and then a beautiful sunset, with a red sky that promises a fine day tomorrow.

Sunshine and showers; blue skies and gray skies; rain, snow, and hail; and wind and calm are all aspects of ordinary day-to-day weather. The weather can change in the course of a day—perhaps several times. It also changes with the seasons. As summer arrives, spring showers and sunshine give way to warmer weather and longer periods of sunshine. These changes occur regularly. We know they are coming and can prepare for them. We check the heating during the summer to make sure it will keep us warm in winter—because we know winter will come. We have winter clothes that are thicker and warmer than those we wear in summer. Maybe we have two sets of tires for the car, one for driving in summer and the other for use in winter, when the roads are covered with ice and snow.

Weather changes all the time. That is why we have weather forecasts. After all, if the weather always stayed the same we would know what it would be like tomorrow and forecasts would be pointless. The scientists who prepare weather forecasts are called meteorologists and the scientific study of weather is meteorology. A "meteor" is any phenomenon that happens in the air. Rain, clouds, dust storms, and anything else you can think of that happens naturally in the air is a meteor. The word comes from the Greek meteoron, which means "lofty," and logos, which means "account," so meteorology is an account of things that happen in the air.

Aristotle (384-322 B.C.E.) was the first person to use the word. He was a Greek philosopher and scientist who wrote on many subjects. Among the 47 of his works that survive, one is called Meteorologica—literally, "an account of lofty things." It is Aristotle's attempt to explain weather phenomena. He gave us our word meteorology and, with it, the idea that such things as clouds, rain, hail, wind, thunder, lightning, and storms can be explained—that they have natural causes and we can understand them. He xvii rejected the traditional explanation, which was that they are caused by the gods, who use the weather to reward or punish humans or simply as a plaything. You cannot explain the supernatural, so in this view you cannot explain the weather, either. Most of Aristotle's explanations were incorrect, but what really matters is that he taught his students to learn about the natural world by observing it closely rather than relying on traditional stories about what other people thought happened. Aristotle gave us the scientific study of weather and the name for it.

Weather is not the same as climate

Of course, your spring day would not be one of rain, sunshine, and a gorgeous red sunset if you lived in Qaanaaq. Qaanaaq used to be called Thule. It is a town of about 600 people in northern Kalaallit Nunaat (the modern name for Greenland). Gazing from your bedroom window on an April morning in Qaanaaq you would see clear, blue skies and a great deal of ice and snow. By early afternoon, the temperature might rise as high as 0.5°F (-17.5°C). It might snow, but this is very unlikely. During April, Qaanaaq receives an average of about 2 inches (40 mm) of snow—when melted, this is equivalent to 0.2 inch (4 mm) of rain. So whatever outdoor activity you had planned for the day you would know that almost certainly the weather would stay fine, and also that you would need to dress warmly. There is only one useful piece of information a weather forecast could provide—the strength of the wind. A strong wind will blow loose, powdery snow from the surface to create a blizzard. You would not want to be caught unawares in a whiteout.

If you lived in Riyadh, the capital of Saudi Arabia, you could look forward to a fine, warm April day. Around dawn, the temperature is probably about 64°F (18°C) and by lunchtime it will have risen to about 89°F (32°C). This will not be too unpleasant, however, because the air is dry and rain is not very likely.

These differences between the weather on any particular day in Qaanaaq, Riyadh, and your own hometown reflect differences in climate. Although the weather in each place varies from day to day and season to season, it does so only within certain limits. Qaanaaq never experiences a scorching-hot day, and the sea never freezes along the coasts of Arabia.

The climate of a place is the average weather it experiences over a long period. On one April day some years ago, the temperature in Qaanaaq reached 37°F (3°C); it has also fallen to -26°F (-32°C). These temperatures really were recorded, but they are included in calculating the average, and the average weather is a more useful guide to the type of climate.

Because they describe average weather, climates can be given names. Most of Arabia has a desert climate, for example, and Kalaallit Nunaat has a polar climate. The classification of climates is complicated, however, and there are several classification systems. Climatology is the scientific study of climates and the scientists who practice it are climatologists. Meteorology and climatology are related but distinct branches of science.

Introduction xix

It is difficult to interpret a record of temperature over a short period. The record (inset) may show the temperature rising and falling, but where does this fit into the long-term climate record?

Climates also change

Weather changes from day to day. Climates also change, but much more slowly. There have been times in the past when they were very different from the climates of today. The land where Chicago now stands once lay beneath a thick ice sheet and the climate was like that of central Kalaallit Nunaat. Beneath the streets and squares of London, England, scientists have found the fossilized remains of hippopotamus and elephants, animals that live in tropical climates.

The world's climates are still changing, but so gradually that detecting the change is difficult. Changes that take place over a few years can be very misleading. It may be true that average temperatures have risen or fallen over the last half-century or so, but this does not mean they will continue to move in the same direction. As the illustration shows, fitting a short-term trend into a long-term pattern is largely a matter of guesswork. That is why the study of past climates is so important—without the historical record, predictions are very unreliable.

Climatology and meteorology are distinct, but both are based on our understanding of the way the atmosphere behaves in response to warm sunshine, the rotation of the Earth, and its contact with the continents and oceans. Climatology and meteorology are atmospheric sciences.

It is difficult to interpret a record of temperature over a short period. The record (inset) may show the temperature rising and falling, but where does this fit into the long-term climate record?

Mars was not always a cold desert

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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