48 Climate Change-High

Climate Change FOCUS Question How is Earth's climate changing?

Warming Up In recent years, severe weather has become more powerful and frequent. The strongest cyclone ever recorded slammed into the Philippines. A drought dried out Australia, and dust storms choked the city of Sydney. Meanwhile, record snowfalls blanketed eastern Canada and the United States. Does this extreme weather mean Earth's entire climate is changing? Yes, and it's just getting started. This is the new reality of climate change. Weather Versus Climate Weather describes the daily conditions in the atmosphere, such as temperature, clouds, rain, or wind. It also includes seasonal trends, such as a very snowy winter or a very hot summer. Climate is the average temperature, wind speed, and rainfall in a region over many years. Climate helps define the average weather in an area, but the day-to-day weather can vary.

The Greenhouse Effect Earth's atmosphere acts like a blanket. The Sun shines on Earth's surface, warming the land and water. Heat that was absorbed by the surface is then released, and some of it is trapped by the atmosphere, keeping Earth warm. This process is called the greenhouse effect. Without it, Earth would be cold and lifeless like the Moon. Some gases in Earth's atmosphere, called greenhouse gases, trap heat better than others— just as some materials, such as wool, make warmer blankets. Carbon dioxide (CO2) is an important natural greenhouse gas. It is the gas you breathe out and the gas plants take in. But too much of it can cause problems. Large amounts of CO2 in the atmosphere trap more heat, causing Earth to heat up even more.

Changing Atmosphere Excess CO2 in the atmosphere comes from burning fuels. Since the early 1900s, cars, airplanes, factories, and power plants have pumped out tons of extra CO2. Adding CO2 to the atmosphere is like adding blankets to a bed. Many of the warmest years in history have occurred in the twenty-first century. Different places on Earth have warmed up at different rates. A few places have even cooled off, but Earth as a whole has warmed. This is known as global warming. Scientists predict that the global average temperature will rise between 2° and 6°C (3.6-10.8°F) by the year 2115. That may not sound like a lot, but even small changes in temperature can mean big changes for Earth.

Changing Ice Normally, about 10 percent of Earth's surface is covered with some form of ice. As Earth warms up, this ice is melting rapidly. Ice sheets are massive slabs of frozen water that cover land. These ice sheets are losing billions of tons of ice per year. Glaciers are rivers of slow-moving ice, often found on mountaintops. It is natural for glaciers to melt a bit in the spring and summer. But now, thousands of glaciers have shrunk quickly, and hundreds of them have vanished entirely. Sea ice is frozen ocean water that floats on the surface. It, too, is shrinking. Do You Know? White ice and snow reflect sunlight back into space. As ice melts, more dark land and water are exposed. This causes Earth's surface to absorb even more heat.

Changing Seas The Arctic Ocean is usually covered with sea ice year round, but in recent summers, scientists have spotted open water, even at the North Pole. Water from melting sea ice, glaciers, and ice sheets is filling the ocean. All that extra water increases the sea level. Since the early 1900s, the sea level has risen 19 centimeters (7.5 in.). This rise has caused flooding in many areas, especially during storms. The sea level is rising for another reason, too. The warmer atmosphere is warming up our oceans, and water expands as it heats up. Warmer waters also change sea life. Fragile coral reefs struggle in water that is too warm. Fish and other animals are moving closer to the poles to find cooler water.