March 16, 2010 – Original Source: The Economic Times
WASHINGTON: A new study has determined 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.
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”, that is, 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.
Solar minimum went on for a little longer than expected during Solar Cycle 24. Unfortunately, it didn’t help our warming climate much.
Scientists have pondered that 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 Dr 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.
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.
But, global warming will overwhelm any “cooling” effect caused by reduced solar output.
According to Julie Arblaster, a climate researcher at the Australian Bureau of Meteorology and the National Center for Atmospheric Research in Colorado, a reduction of 0.25 percent in solar irradiance 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,” she said.