Solar radiation
Is solar activity responsible for global warming?
Fluctuations in solar activity are natural. Satellite-based instruments have been measuring the amount of solar energy reaching the top of the atmosphere (also known as total solar irradiance, or TSI in short) since the late 1970s. The average value of TSI is found to be about 1361 W/m2.
While solar activity follows a cycle of roughly 11 years, the average fluctuation of TSI over the past several solar cycles is only about 0.1%. For pre-satellite times, TSI variations had to be estimated from sunspot numbers or radioisotope analysis of polar ice and tree rings.
As shown in Fig 2.3, both total solar radiation and global mean temperature showed upward trends in the early 20th century. However, total solar radiation showed a downward trend since the 1960’s while global mean temperature continued to rise.
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| Fig 2.3 Change in total solar radiation and global mean temperature ii (Source: Skeptical Science ) |
★ Teachers reference -Temperature variations in troposphere and stratosphere
If solar activity is the main cause of global warming, the temperature of the whole atmosphere will be affected. If global warming is mainly caused by greenhouse gases, the increase in greenhouse gases will raise the temperature in the lower troposphere but the lower stratosphere will cool. This is a distinctive characteristic of an intensifying greenhouse effect. Observations show that there is a long-term warming trend in the lower troposphere but a long-term cooling trend in the lower stratosphere.
IPCC WGI AR5, Chapter 2, Figure 2.24
www.climatechange2013.org/images/report/WG1AR5_Chapter02_FINAL.pdf
Why the Sun is not responsible for recent climate change
www.carbonbrief.org/why-the-sun-is-not-responsible-for-recent-climate-change