In our October 11, 2010, cover story, “A Message From Mother Nature?” you’ll read about the increase in the number of extreme weather events. Many scientists believe that climate change is contributing to this phenomenon, but they admit that they can’t prove it. What is the difference between weather and climate? Weather refers to specific, short-term events such as a snowstorm or a sunny day. Climate refers to weather patterns or trends in an area over a long period of time.

An “ice age” is a period of hundreds or even millions of years when Earth’s atmosphere is much colder than usual. The last one ended about 10,000 years ago. Glaciers (thick sheets of ice) covered much of Earth. As the atmosphere gradually warmed, the glaciers receded. Water from melted ice-age glaciers formed North America’s Great Lakes. Remaining glaciers, such as the icefields in northwestern Canada shown here, have been melting more rapidly than in the past. If this continues, sea levels could rise, flooding some coastal areas.

In the late 18th century, people began to use more machines to do work once done by hand. This picture shows an early steam engine being used to help miners. Much of the energy that powers the machines and other technologies we rely on today comes from the burning of fossil fuels— coal, oil, and natural gas. Burning fossil fuels produces large quantities of carbon dioxide (CO 2 ) and other “greenhouse gases.” Scientists believe that these gases trap heat in Earth’s atmosphere.

Since the Industrial Revolution, Earth’s average global temperature has risen by 1.4°F. Most, but not all, scientists see a connection between human activity and the increase in temperature. If Earth continues to get hotter, more extreme weather is likely. Heat waves will be hotter, rainstorms more severe, and snowstorms heavier.

A drought is a long period with little or no rain. Water supplies dry up, crops die, and the chance of wildfires increases. A two-year drought dried up parts of Lake Lavon in north Texas (shown here, in 2006). The lake recovered when rains finally came—only to be threatened by another dry spell last year. Drought knows no boundaries. Africa’s Sahara Desert has been expanding as drought reduces nearby grasslands to windblown dust.

Over the past 10 years, Australia’s average rainfall has been less than half the normal average. Water- conservation rules are now in place. In 2009, the worst wildfires in the country’s history killed 173 people and thousands of animals. Thick smoke polluted areas far beyond the fire sites. The same year, a four-day heat wave of 110°F and up killed 200 people in Melbourne. Railroad tracks warped, and more than 4,000 flying foxes died and fell out of trees.

The summer of 2010 was the hottest in Russian history. Five times in two weeks, temperatures in Moscow rose above the previous record of 97°F. Wildfires like the one shown here burned outside Moscow for weeks, destroying a third of Russia’s wheat crop. Moscow was overwhelmed by smoke from the fires. The combination of heat and air pollution killed an estimated 15,000 people.

Some places around the world are getting more rain than normal, which can cause devastating floods. In March 2010, the heaviest rains on record in Rhode Island resulted in the worst flooding there in 200 years. In August, unusually heavy monsoon rains in Pakistan caused the Indus River to overflow. The floods killed an estimated 1,600 people and displaced 21 million, including the family in this photograph.

1. Is a thunderstorm an example of weather or climate? What is the difference between the two? 2. Why do scientists think that global warming is producing more hurricanes? 3. Do you think human activity is contributing to climate change? Why or why not?