By Bethany Decourten
While the sun may rise and set dependably every day, fluctuations in the amount of energy that reaches the Earth’s surface have been observed by scientists for the past 400 years. In fact, the surface of the sun is a very active and dynamic environment. Sun spots are described as storms on the sun’s surface that are slightly cooler than their surroundings, giving them the appearance of dark spots when observed from Earth. Areas around sun spots have an intensified magnetic field that increases the likelihood of solar flares, during which the Earth can be exposed to increased solar irradiance. An increase in solar energy reaching the Earth’s surface has the potential to effect its climate. The occurrence of sunspots fluctuates on an 11-year cycle that correlates to periodic warming and cooling of the Earth’s surface temperatures. Sustained highs and lows of solar activity can have increasingly strong effects on our climate. The historic cooling period of the Earth between 1450 and 1850, known as The Little Ice Age, corresponds to a period during which very few sunspots were observed. The opposite effect was observed during the Medieval Warming Period, during which there was an increase in sun spot occurrence. Emerging evidence suggests that sunspot activity has doubled over the last century. These patterns of solar activity have been considered as possible contributing factors to the observed changes in global temperatures.
So, is the fate of the Earth’s climate simply written in the star?
Over 70% of the Earth’s surface is covered by water. The thermal properties of water enable our oceans to curtail warming caused by the periodic increases in solar irradiance. However, anthropogenic activity, such as the production of greenhouse gasses, is causing ocean temperatures to increase. Warmer oceans are not able to inhibit warming caused by increased solar activity as effectively as they have in the past. Polar ice caps reflect much of the solar energy back into space and prevent this energy from warming the Earth’s surface. As Polar Regions warm due to human-induced climate change, sea ice begins to melt and the amount of solar energy that reaches the Earth increases, causing further warming. The Earth is also protected by a layer of atmospheric gas called ozone, which functions to filter out harmful ultraviolet (UV) light and decrease the solar irradiance that reaches the Earth’s surface. Anthropogenic pollution has led to depletion of the ozone, reducing its ability to mediate the effects of solar activity. While the increased occurrence of sunspots has the potential to contribute minutely to global temperature increases, anthropogenic activity has hindered the natural processes that moderate the climatic response to increased solar irradiance. Most scientists agree that observed solar activity alone will have only a minimal effect on global warming trends.
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Fröhlich, Claus. (1998). The Sun’s total irradiance: Cycles, trends and related climate change uncertainties since 1976. Geophysical Research Letters. Vol. 25: 23 pages 4377-4380.