Several key climate science studies, including those by the U.S. Global Change Research Program and the Intergovernmental Panel on Climate Change, concluded that human-caused emission of heat-trapping or "greenhouse" gases, such as carbon dioxide (CO2), are the primary cause of climate change.
Climate scientists have found that the amount of greenhouse gases in Earth's atmosphere increased dramatically starting in the mid-19th century, correlating with the industrial revolution and the rise of fossil-fuel transportation, among other factors. Climate change accelerated when humans began pumping more heat-trapping gases into the atmosphere at a rate faster than Earth had ever experienced before. Levels of CO2 and methane (another greenhouse gas) in the atmosphere are higher now than in the last 650,000 years. If humans continue burning more and more fossil fuels, scientists believe the impacts of climate change will accelerate in the future.
One society's output of greenhouse gases affects all people on the planet. Wind currents and other atmospheric conditions ensure that the gases are not contained to one geographic area. Scientists have a high certainty about global trends but are less certain about the future of specific regional or local climates. Scientists work with state-of-the-art computer models and new data collection methods to sharpen our picture of climate change from worldwide to local scales.