Various independent historical measurements conclude that the global average surface temperature has increased by about 3.3°F (0.5°C) over the past one hundred years. Whether the rise in the Earth’s average surface temperature is due to human or natural increases in carbon dioxide output is a controversial topic, although more scientists are leaning toward human-driven causes. Cited for contributing to increased atmospheric carbon dioxide includes the burning of fossil fuels, volcanic activity, destruction of the rain forests, use of aerosols, and an increase in agricultural activity.