Recent warming cannot be explained by the Sun or natural factors alone
There are many factors which may contribute to climate change. Only when all of these factors are included do we get a satisfactory explanation of the magnitude and patterns of climate change over the last century.
Over the last 1,000 years most of the variability can probably be explained by cooling due to major volcanic eruptions and changes in solar heating.
In the 20th century the situation becomes more complicated. There is some evidence that increases in solar heating may have led to some warming early in the 20th century, but direct satellite measurements show no appreciable change in solar heating over the last three decades. Three major volcanic eruptions in 1963, 1982 and 1991 led to short periods of cooling. Throughout the century, CO2 increased steadily and has been shown to be responsible for most of the warming in the second half of the century.
As well as producing CO2, burning fossil fuels also produces small particles called aerosols which cool the climate by reflecting sunlight back into space. These have increased steadily in concentration over the 20th century, which has probably offset some of the warming we have seen.
Changes in solar activity do affect global temperatures, but research shows that, over the last 50 years, increased greenhouse gas concentrations have a much greater effect than changes in the Sun's energy.
