This energy comes from the sun. The output decresed by an estimated 0.1% in the 1980s. If this trend continues, it could influence global climate. A 1% change in solar output could increase or decrease global temperature by 0.5-1 degee. Scientists believe that solar output triggered the "Little ice age".
Sunspots are storms on the sun's surface, marked by intense magnetic activity. Scientists believe that the number of sunspots cycles over time, reaching a peak every 11 years. The sun gets hotter when there are more sunspots.
Surface reflection is the reflecting power of the Earth's surface. During cooler periods whn there is more snow and ice on the ground, global temperatures will drop as a result of the snow and ice reflecting sunlight back into space. If the planet warms, the snow and ice will melt and the Earth won't be able to reflect sunlight as well, so temperatures will continue to rise.
When a volcano erupts, it throws out large volumes of sulphur dioxide, water vapor, dust and ash into the atmosphere. Millions of tonnes of sulphur dioxide can reach the upper levels of the atmosphere. These volcanic emissions act as a blanket and reduce the amount of solar radiation reaching the Earth's surface.
The ash emmitted during the 1991 erruption of Mount Pinatubo reached the stratosphere and spread around the globe in 12 months.