Solar-Terrestrial Physics
Division Solar-Terrestrial Physics
Division Space weather may also in the long term affect the Earth's climate. Solar ultra-violet, visible and heat
radiation are the primary factors for the Earth's climate, including global average temperatures, and
these energy sources appear to be quite constant. However, many scientists have observed corrrelations
between the solar magnetic activity, which is reflected in the sunspot frequency, and climate parameters
at the Earth. Sunspots has been recorded through several hundreds of years which makes it possible to
compare their variable frequency to climate variations to the extent that reliable climatological
records exists. One of the most striking comparisons was published by E. Friis-Christensen og
K. Lassen, DMI, in "Science" in 1991.
In their work they compared the average temperature at the
northern hemisphere with the average solar activity defined through the interval between successive
sunspot maxima. The more active the sun - the shorter the interval: the solar cycle runs more intense.
Their results are displayed in the figure below:
The red curve illustrates the solar activity, which is generally
increasing through an interval of 100 years, since the cycle lenght has decreased from around 11.5
years to less than 10 years. Within the same interval the Earth's average temperature as indicated
by the black curve has increased by approximately 0.7 degree C. Even the finer structures in the two
curves have similar appearances.
(Reference: Friis-Christensen, E., and K. Lassen, Length of the solar
cycle: An indicator of solar activity closely associated with climate, Science, 254, 698-700, 1991).
Solar-Terrestrial Physics Division Homepage
Danish Meteorological Institute Homepage
Updated Sep. 27 1998.