WHY DOES IT MATTER?
As greenhouse gas emissions from human activities increase, they build up in the atmosphere and warm the climate, leading to many other changes around the world—in the atmosphere, on land, and in the oceans. The indicators in other chapters of this report illustrate many of these changes. Such changes have both positive and negative e ects on people, society, and the environment—including plants and animals. Because many of the major greenhouse gases stay in the atmosphere for tens to thousands of years after being released, their warming e ects on the climate persist over a long time and can therefore a ect both present and future generations.