evidence: The Earth is heating up, and human beings burning fossil fuels are the dominant cause. It’s not ocean warming that dominates, it’s not cosmic rays, it’s not variations in the Earth’s orbit and tilt toward the sun (Milankovitch cycles), it’s not solar irradiance – it’s us. But there is a very vocal minority that refuses to accept that global heating is real. [...] First, there is a correlation between sunspots and solar irradiance (output) on the Earth. During this period, sunspots were less common and there was less solar energy reaching the Earth, allowing it to cool slightly. Second, there were several volcanic eruptions that released massive amounts of sulfur dioxide into the atmosphere. Sulfur dioxide is an aerosol that forms droplets of sulphuric acid in the high atmosphere and reflects solar energy back into space, so these two volcanic eruptions had some short- to medium-term effects. In addition, prior to the 1970s there were limited pollution controls, allowing pollutant aerosols to act as coolants via reflection of solar radiation. Ultimately, though, it is believed that sometime after 1970 the concentration of CO2 rose to the point that solar forcing was no longer the dominant climate factor, anthropogenic CO2 was. (Sources: Do Models Underestimate the Solar Contribution to Recent Climate Change?, Swindled!)