Lesson 10: Global Warming, Advocacy
Global warming refers to an unequivocal and continuing rise in the average temperature of Earth’s climate system. Since the early 20th century, when accurate records began being kept, the global air and sea surface temperature has increased about 0.8 °C (1.4 °F). Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850. In the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1400 years.
Scientific understanding of the cause of global warming has been increasing. In its fourth assessment of the relevant scientific literature, the Intergovernmental Panel on Climate Change (IPCC) reported that scientists were more than 90% certain that most of global warming was being caused by increasing concentrations of greenhouse gases produced by human activities.