During the past century, human activities have released large amounts of carbon dioxide and other greenhouse gases into the atmosphere. Most of the gases come from burning fossil fuels to produce energy. Greenhouse gases are like a blanket around the Earth, trapping energy in the atmosphere and causing it to warm. This is called the greenhouse effect and it is natural and necessary to support life on earth. However, while greenhouse gases buildup, the climate changes and result in dangerous effects to human health and ecosystems. People have adapted to the stable climate we have enjoyed since the last ice age which ended several thousand years ago. A warmer climate can bring changes that can affect our water supplies, agriculture, power and transportation systems, the natural environment, and even our own health and safety. There are some climate changes that are unavoidable and nothing can be done about it. For example, carbon dioxide can stay in the atmosphere for nearly a century, so Earth will continue to warm in the future.