quote: Changes in the Sun's brightness over the past millennium have had only a small effect on Earth's climate, according to a review of existing results and new calculations performed by researchers in the United States, Switzerland, and Germany.
quote: Warming by the Sun and other variations in natural systems cannot explain global warming... The simulations that include only natural variability, including changes in the Sun and eruptions of volcanoes, show that we should have seen a decrease in the global average temperature in the last several decades.The simulations that most closely resemble the observed record are the ones that take the cooling effect of air pollution and the warming effect of greenhouse gases into account.
quote: According to Shindell, the new study also confirms that changing levels of energy from the sun are not a major cause of global warming.Many scientists have argued that the radiation change in a solar cycle — an increase of two to three tenths of a percent over the 20th century — are not strong enough to account for the observed surface temperature increases. The GISS model agrees that the solar increases do not have the ability to cause large global temperature increases, leading Shindell to conclude that greenhouse gasses are indeed playing the dominant role.