<p> Earth's climate has always varied, but it is now changing more rapidly than at any other time in recent centuries. The climate is very complex, and many factors play important roles in determining how it changes. </p> <p> Why is the climate changing? Could Earth be getting warmer by itself? Are people doing things that make the climate warmer? </p> <p> Award-winning science writer Seymour Simon teams up with the Smithsonian Institution to give you a full-color photographic introduction to the causes and effects of global warming and climate change. </p>