Global Warming Earth has often warmed and cooled throughout the course of its lengthy history. The planet's climate has altered as a result of tiny orbital changes, changes to the atmosphere or surface, and variations in the Sun's radiation. But in the last century, another force—humanity—has begun to affect Earth's climate. How does current warming compare to earlier climatic shifts on Earth? How can we be convinced that greenhouse gases created by humans are the reason for the warming? When will the Earth's temperature rise? How is Earth going to react? The biggest scientific problem of our time may be figuring out the answers to these questions.