People who don't want to face having to clean up theenvironment like to blame global warming on the increasedsunspot activity. But researchers who have studied theincidence of sunspots since 850 AD have shown that whileglobal warming correlates with increased solar activity,warming has increased dramatically in the last 30 years,while the sun has remained the same.
This means that while the sun may be responsible for earlierwarming, it can't be blamed for the recent increase intemperatures that is pushing us over the edge towardsclimate change.
Astronomers have been observing sunspots since the inventionof the telescope in the early 17th century. The number ofsunspots varies over an 11-year cycle, but his cycle canvary. In the second half of the 17th century, there werehardly any sunspots at all, while today?s sunspot activityhas gone on much longer than expected.
Sunspot history can also be tracked from measurements ofberyllium-10 in ice cores from Greenland and the Antarctic.This radioactive isotope is created when cosmic rays enterthe Earth?s atmosphere. A comparison of the Beryllium-10data with the historical records of sunspot numbers revealsa high degree of correlation, meaning that both methods ofgathering sunspot data are valid.
The sun has been in a state of unusually high activity forabout 60 years. Another period of high solar activity, butwith many fewer sunspots, occurred in the Middle Ages from1100 to 1250. This was when the Vikings establishedsettlements in Greenland, since it was much warmer than usual.
The researchers have learned that variations on the surfaceof the sun run parallel to climate change most of that time,showing that the Sun has definitely influenced the climatein the past. However, it's also clear that since about 1980,the Earth has warmed up considerably while the sun hasstayed about the same. Solar Physicist Sami K. Solanki says,"?The significant increase in the Earth's temperature since1980 is indeed to be ascribed to the greenhouse effectcaused by carbon dioxide."
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