evidence: The second reason that scientists think the current warming is not from natural influences is that, over the past century, scientists from all over the world have been collecting data on natural factors that influence climate—things like changes in the Sun’s brightness, major volcanic eruptions, and cycles such as El Niño and the Pacific Decadal Oscillation. These observations have failed to show any long-term changes that could fully account for the recent, rapid warming of Earth’s temperature. Finally, scientists know that carbon dioxide is a greenhouse gas and that it is released into the air when coal and other fossil fuels burn. Paleoclimate data show that atmospheric carbon dioxide levels are higher than they have been in the past 800,000 years. There is no plausible explanation for why such high levels of carbon dioxide would not cause the planet to warm. [...] - Lockwood, M., & Fröhlich, C. (2008). Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature. II. Different reconstructions of the total solar irradiance variation and dependence on response time scale. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 464(2094), 1367-1385.