Earth is warming up. The average global temperature in 2014 was the warmest since record keeping began in 1880. In fact, 14 of the 15 hottest years have occurred during the twenty-first century.
Why does that matter? It means the planet’s climate is changing. Our climate has warmed and cooled very gradually in the past. It was driven mostly by natural causes, such as variations in Earth’s orbit. But scientists believe that human activity is now changing the climate quickly. One result is that weather is becoming more extreme.
Weather is called extreme when it is dangerous or unusual. Droughts, hurricanes, tornadoes, and other fierce storms are examples of extreme weather.
