Global warming is the rising average temperature of Earth's atmosphere and oceans. The effect of global warming was noted in the late 19th century and it is projected to continue. Since the early 20th century, Earth's average surface temperature has increased by about 0.8 °C (1.4 °F), with about two thirds of the increase occurring since 1980. The warming of the climate system is unequivocal, and scientists are more than 90% certain that most of it is caused by increased concentrations of greenhouse gases produced by human activities such as deforestation and the burning of fossil fuels. These findings have been recognized by the national science academies of all major industrialized nations. Global warming is important as changes affect weather patterns which contributes to extreme weather events which in turn impacts food production. If we, as a society, do not manage global warming, we will face tremendous challenges in the near future.