Professor Mike dePledge speaking on Climate Change and Health

Early in Earth's history the sun emitted only 70% as much power as it does today. With the same atmospheric composition as exists today, liquid water should not have existed on Earth. However, there is evidence for the presence of water on the early Earth, in the Hadean internet marketing and Archean eons, leading to what is known as the faint young sun paradox. Hypothesized solutions to this paradox include a vastly different atmosphere, with much higher concentrations of greenhouse gases than currently exist and a stronger solar wind that could shield the Earth from the cooling effects of cosmic rays. Over the following approximately 4 billion years, the energy output of the sun increased and atmospheric composition changed, with the oxygenation of the atmosphere being the most notable alteration. The luminosity of the sun will continue to increase as it follows the main sequence. These changes in luminosity web hosting, and the sun's ultimate death as it becomes a red giant and then a white dwarf, will have large effects on climate, with the red giant phase possibly ending life on Earth.Solar output also varies on shorter time scales, including the 11-year solar cycle and longer-term modulations. The 11-year sunspot cycle produces only a small change in temperature near Earth's surface (on the order of a tenth of a degree) but has a greater influence in the atmosphere's upper layers. Solar intensity variations are considered to have been influential in triggering the Little Ice Age and for some of the warming observed from 1900 to 1950. The cyclical nature of the sun's energy output is not yet fully understood; it differs from the very slow change that is happening within the sun as it ages and evolves dedicated hosting, with some studies pointing toward solar radiation increases from cyclical sunspot activity affecting global warming.