Solar Variability Most Likely Not the Cause of Global Warming

by Ian O'Neill on February 21, 2008

Solar variability effects on the climate are probably not a cause of global warming (credit: Ian ONeill)
The gradual increase in global temperatures is getting harder and harder to pin on the Sun and its energy output variability. The Sun has a variation in how much energy it outputs but this variability is only about one tenth of one percent. The pattern of atmospheric heating since the 1960s is showing an increase with the increase in human activity (industry, transportation, power generation) and neither are showing signs of slowing down…

At the American Association for the Advancement of Science (AAAS) meeting in Boston, many talks are focusing on climate change and the human impact on the Earth. Experts in solar science, climate modeling, and atmospheric science are exploring the issues surrounding what the main culprit behind the rapid rate of change in global temperatures could be. The sole energy input into the Earths atmosphere comes from the Sun; so many scientists have looked toward our star for the answers. The Sun does vary its output of energy (historically, this is obvious during long periods of solar inactivity, such as the Maunder Minimum in the 1600’s where hardly any sunspots were observed on the Sun – this reduction in activity has been linked to the “Little Ice Age” experienced during this time), but generally speaking, the net energy increase or decrease is very small.

The link between solar variability and global warming has taken another blow from analysis of historical samples of sediment containing radioactive carbon-14 and a beryllium isotope. Quantities of carbon-14 and beryllium-10 reflect solar activity as they are greatly affected by solar magnetic field strength. The Sun’s magnetic field is directly related to solar activity (and therefore sunspot population). These radioactive isotopes are created by the impact of cosmic rays in the Earths atmosphere, and should the solar magnetic field be strong (i.e. during periods of high activity), cosmic rays will be blocked, reducing the quantity of isotopes in the sediment.

However, results from this analysis appear inconclusive and no strong link can be found in favour of increased solar activity during periods of atmospheric heating.

Linking any atmospheric phenomenon with solar variability is a difficult task. Attempts to connect monsoons with the 11-year solar cycle for instance have failed in 150 years of trying. It would seem that, for now at least, any connection between increased solar energy output and global warming is tenuous at best.

Casper M. Ammann, climate modeler at the National Center for Atmospheric Research in Boulder, Colorado, points out that global temperatures are rising at a historic rate, and there remains no link between solar variability and global warming. He states that global warming has “nothing to do with changes in solar activity. It’s greenhouse gases. It’s not the sun that is causing this [climate] trend.”

Perhaps the only answer is to drastically cut back our dependence on fossil fuels to slow the rate of carbon dioxide production. Even if the Sun should decide to become inactive, as there appears to be very little relationship between solar output and global warming, we will not be able to escape the greenhouse gases heating up our climate.



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Hello! My name is Ian O'Neill and I've been writing for the Universe Today since December 2007. I am a solar physics doctor, but my space interests are wide-ranging. Since becoming a science writer I have been drawn to the more extreme astrophysics concepts (like black hole dynamics), high energy physics (getting excited about the LHC!) and general space colonization efforts. I am also heavily involved with the Mars Homestead project (run by the Mars Foundation), an international organization to advance our settlement concepts on Mars. I also run my own space physics blog:, be sure to check it out!

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