Scientists now know for certain that the earth has been warming for the past century. They know that human activities, mainly the burning of coal and oil, have dramatically increased concentrations of heat-trapping gases in the atmosphere. And they understand the science of how these gases are causing the observed warming.
As a result, they predict that the world will continue to warm in the centuries ahead, with significant impacts on sea levels and weather patterns, and consequences for human health, ecosystems, and the economy. Avoiding the most severe impacts, scientists say, will require substantial reductions in emissions of the greenhouse gases that are contributing to climate change.