The Sun Can't Save Us From Global Warming

The sun contributes almost all of the energy into our atmosphere through electromagnetic radiation, so when our nearest star reduces its output, one would think that our atmosphere would cool down (or, at least, wouldn't heat up).

This is true, partially.

But a new study published in the journal Geophysical Research Letters says that even if the sun commenced a very long period of low activity, it cannot put the brakes on the relentless rise of global temperatures caused by greenhouse gases.

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Since the 13th century, the sun has gone through four "Grand Minima", one of which is thought to have contributed to the anomalously low temperatures in Europe in the 17th and 18th centuries. This extended cold period (known as the "Little Ice Age") coincided with a very long period of calm on the solar surface.

Tracking sunspot numbers, astronomers noticed that from 1645 to 1715, the sun's disk was "blank" (i.e. it had few, if any, sunspots). This period became known as the "Maunder Minimum".

If the sun lacks spots, that means there is a reduction in magnetic energy, signifying a lower energy output (or a slight reduction in brightness, or "irradiance"). Typically, every 11 years, the sun goes through peaks and troughs in energy output (known as solar maximum and minimum, respectively) and this abnormally long minima is largely attributed with contributing toward the Little Ice Age.

So, what if the sun endures another Grand Minimum? Could the solar cycle slow down -- or even reverse -- the amplified global heating caused by greenhouse gas emissions?

"The notion that we are heading for a new Little Ice Age if the sun actually entered a Grand Minimum is wrong," said study lead author Georg Feulner of the Potsdam Institute for Climate Impact Research.

If greenhouse gas emissions continue to increase unchecked, global average temperatures are predicted to rise by between 3.7 degrees Celsius and 4.5 degrees Celsius by the end of the 21st century. (According to UN-appointed climatologists, global average temperatures have already risen by 0.7 degrees Celsius since the Industrial Revolution.)

And what if the sun enters another Grand Minimum? The reduction in solar energy will slow heating by a paltry 0.3 degrees Celsius by the end of this century.

The sun can't bail us out of this one; global warming will overwhelm any "cooling" effect caused by reduced solar output.

Julie Arblaster, a climate researcher at the Australian Bureau of Meteorology and the National Center for Atmospheric Research in Colorado, says that the conclusions of this most recent study agree with previous work carried out when trying to understand the complex relationship between the sun and the Earth's atmosphere.

However, she points out that a reduction of 0.25 percent in solar irradiance (as used in this study) is "on the extreme end of what we would expect for the next century."

"This shows that any changes in the Sun, even large changes, will only have a small impact in offsetting that warming."

Although it may be tempting to think that a reduction in solar energy output could cool our global temperatures, unfortunately this isn't the case. Carbon dioxide (and other greenhouse gases) are too efficient at trapping the sun's energy (even if that energy did drop by 0.25 percent) to make any difference.

This underscores the need for emissions management before more extreme measures are considered by future generations.