What are the causes of Climate Change?

Because the Sun is the essential source of energy that drives our climate system, it's appropriate to presume that changes in the Sun's energy output will cause the climate to change.

Solar variability has been shown to play a role in previous climate changes in experiments. For example, between around 1650 and 1850, a decrease in solar activity combined with an increase in volcanic activity is believed to have aided in the onset of the Little Ice Age, when Greenland cooled from 1410 to the 1720s and glaciers advanced in the Alps.

However, some lines of evidence show that current global warming is unrelated to changes in solar energy:

• The average amount of energy emitted by the Sun has remained constant or risen slightly since 1750.
• Warmer temperatures would be expected in all layers of the atmosphere if the warming was caused by a more active Sun. Instead, they've noticed a cooling in the upper atmosphere, as well as a warming at the surface and in the lower atmosphere because greenhouse gases trap heat in the lower atmosphere.
• Climate models that account for changes in solar irradiance are unable to replicate the observed temperature trend over the past century or more without accounting for an increase in greenhouse gas emissions.