It’s all to do with the sun – for example, there is a strong link between the increased temperature on earth and the number of sunspots on the sun.
But what does the science – and the Royal Society – say?
Change in solar activity is one of the many factors that influence the climate but cannot, on its own, account for the change in global average temperature that we have seen in the 21st century.
Changes in the sun’s activity influence the earth’s climate through small but significant variations in its intensity. When it is a more “active” phase – as indicated by a greater number of sunspots on its surface – it emits more light and heat. While there is evidence of a link between solar activity and some of the warming in the early 20th century, measurements from satellites show that there has been very little change in underlying solar activity in the last 30 years. There is even evidence of a detectable decline – and so this cannot account for the recent rises we have seen in global temperatures. The magnitude and pattern of changes to temperatures can only be understood by taking all of the relevant factors – both natural and human – into account. For example, major volcanic eruptions produce a cooling effect because they blast ash and other particles into the atmosphere where they persist for a few years and reduce the amount of the sun’s energy that reaches the earth’s surface. Also, burning fossil fuels produces particles called sulphate aerosols which tend to cool the climate in the same way. Over the first part of the 20th century higher levels of solar activity combined with increases in human generated carbon dioxide to raise temperatures. Between 1940 and 1970 the carbon dioxide effect was probably offset by increasing amounts of sulphate aerosols in the atmosphere, and a slight downturn in solar activity, as well as enhanced volcanic activity.
During this period global temperatures dropped. However, in the latter part of the 20th century temperatures rose well above the levels of the 1940s. Strong measures taken to reduce sulphate pollution in some regions of the world meant that industrial aerosols began to provide less compensation for an increasing warming caused by carbon dioxide. The rising temperature during this period has been partly abated by occasional volcanic eruptions.