Global climate change is just as the phrase implies: the change in the global climate. The Earth has been through numerous global climate changes in the past; for example, the planet has had numerous periods of global temperate climates (for example, glaciations) followed by warming. These changes in the climate have always been attributed to natural causes: for example, a rise in temperatures caused by intense volcanic activity or changes in climate due to asteroids or comets striking the surface, throwing material into the atmosphere, changing the intensity of sunlight, thus altering the climate. Modern global climate change, according to what seems to be the majority of scientists, is due to human-generated greenhouse gases. Since the Industrial Revolution, the increase in greenhouse gases is thought to have caused an increase in global surface temperatures, raised worldwide sea levels, and changed the habitats of various organisms—not to mention caused extinctions—in its wake.