The sun helps maintain Earth’s climate to be warm enough for us to survive. Even subtle changes in Earth’s orbit around the sun have led to and ended past ice ages. This relationship between Earth’s climate and its orbit around the Sun is well known.
The sun’s activity and appearance goes through cycles, with one solar cycle taking 11 years to complete. The current cycle began at the end of 2019 and will reach peak levels of activity in 2025. During a solar cycle, the amount of solar radiation reaching Earth varies. These changes have a variety of effects on Earth’s atmosphere, including auroras.
The amount of solar energy Earth receives follows the sun’s natural 11-year cycle of small ups and downs with no net increase since the 1950s. During this same time period, our global temperature has increased over 0.8 degrees C. This warming of Earth over the last few decades is too rapid to be caused by the observed solar activity.
Greenhouse gases in the atmosphere raise the surface temperature through absorption of radiation at wavelengths Earth emits to space. These gases play a crucial role in Earth’s climate by affecting our energy budget. They warm the planet. The three most abundant greenhouse gases in Earth’s atmosphere are: water vapor, carbon dioxide, and methane.
Humans have been altering weather and climate on local and regional scales for centuries. One of those impacts is through activities that increase the concentrations of greenhouse gases. Since the beginning of the Industrial Revolution, human activities have increased atmospheric carbon dioxide amounts by over 50% and methane levels by 150%. These rates of increase align with the observed trends in global warming.
Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.
