The Climate Change Skeptic’s Argument: Natural Solar Cycles or Human Activity?


Big Idea

The patterns of contemporary climate change we see, such as rising temperatures and sea levels, rapidly retreating glaciers, lengthening growing seasons, and longer ice-free seasons in the ocean are outcomes of contemporary climate change and a warming planet. To what degree can these changes be explained by natural factors, such as changes in incoming solar radiation to the Earth? Examine Total Solar Irradiance data, and evaluate whether contemporary global climate change can be explained by the variable energy output of our nearest star.

Data Activity

Sunspots and Total Solar Irradiance


The sun has a well-known 11-year sunspot cycle that produces variation in energy output. Solar irradiance has been measured by satellites daily since the late 1970s, and this known solar cycle is incorporated into climate models. Evidence from historical sunspot observations, tree-ring measurements, and other proxy climate data sources show that solar output has not been constant over time. In this activity, we explore whether changes in incoming solar radiation can explain all or part of the warming trend we have seen in Earth’s planetary temperatures.


This module is aligned to the following national learning and curriculum standards:


In this module, you will:

  1. Review the evidence for a relationship between sunspot cycles and total solar irradiance reaching the Earth’s system.
  2. Analyze data to understand the relative influence of solar variability on today’s climate.
  3. Reflect on how climate change skepticism in the media impacts GCC instruction in the classroom.

Keeping Notes

We recommend you set up a journal to take notes as you participate in this experience. Your journal can be an online tool or offline notebook – whichever works for you and your learning style.

Background Information

Our climate system is highly sensitive to both incoming and outgoing radiation. Some of the solar energy that arrives at Earth is reflected back out to space, while another part of the energy going back to space from the Earth is emitted by the Earth. The solar radiation absorbed by the Earth increases the planet's temperature, while energy emitted from the surface of the Earth and absorbed by the atmosphere increases the Earth’s surface temperature (i.e., the greenhouse effect). This absorbed energy is eventually transferred both back to space and redirected again to the Earth's surface.

Solar energy is a key variable in the climate system. Total Solar Irradiance varies in response to magnetic activity in the Sun’s core. Increases in the Sun’s output are typically associated with times of higher solar activity, which is marked by the appearance of increased sunspots, or darker, cooler regions, on the face of the Sun. Though sunspots send less light toward Earth, they are typically surrounded by brighter areas, called faculae, which are a few percent brighter than the average Sun. The brightness of faculae compensates for sunspot darkening, so that the combined effect of faculae and sunspots results in a net increase in incoming solar energy. For this reason, times of increased sunspot activity are also times when Total Solar Irradiance is increased.

The amount of energy that flows from the Sun to Earth is so large that even small fluctuations in the Sun’s output can cause significant changes in the Earth’s climate. One example of solar forcing of climate is known as the “Little Ice Age” (circa 1600-1850). During one 30-year stretch in the 1600s — the coldest period of the Little Ice Age when winter temperatures in Europe were from 1 to 1.5°C cooler than average - astronomers observed a total of only 50 sunspots, indicating a very quiet Sun. In contrast, the Sun has been more active in recent decades, displaying 160 sunspots or more in one 11-year cycle.

Thus, we have evidence that solar cycles or “natural cycles” can influence climate, so could the warming trend we see today be the result of solar activity? We will explore this question in this module.


This professional development experience was funded by NASA's Global Climate Change Education Initiative. This initiative is designed to improve the quality of the nation's STEM (Science, Technology, Engineering, and Mathematics) education and enhance students' and teachers' literacy about global climate and Earth system change from elementary grades to lifelong learners.

Global Climate Change Modules

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