evidence: The concentration of CO2 in the Earth’s atmosphere has increased dramatically over the last 150 years, from a pre-industrial era concentration of approximately 280 parts per million (ppm) to more than 410 ppm currently. CO2 concentration levels are unlikely to dip below these annual averages for hundreds of years. [...] This information tells scientists that human-caused fossil fuel emissions have been the main contributor to the rise in CO2 concentrations since the pre-industrial era. [...] Similarly, an authoritative 2014 report by the Intergovernmental Panel on Climate Change, written and reviewed by hundreds of climate experts and scientists from countries around the world, states unambiguously: "Human influence on the climate system is clear, and recent anthropogenic emissions of green-house gases are the highest in history. […] Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia."