Opponents of the Kyoto treaty claim that the cause of global warming is caused mostly by increased solar activity and not by greenhous gases caused by human activities. Below a clarification about this issue.

Science Daily
October 2, 2003

New research on the sun's contribution to global warming is reported in this month's Astronomy & Geophysics. By looking at solar activity over the last 11,000 years, British Antarctic Survey (BAS) astrophysicist, Mark Clilverd, predicts that the sun's contribution to warming the Earth will reduce slightly over the next 100 years.

This is a different picture to the last century when solar flares, sunspots and geomagnetic storms, increased in number. This rise is simultaneous with emissions of greenhouses gases and an estimated increase in solar heat output, which together have warmed the Earth's temperature by a global average of 0.7 degrees centigrade.
The solar contribution to the increase is variously estimated to be around 4-20% leaving greenhouse gases to make up the remaining 80%.

Note from HHO:

Confounding efforts to determine the Sun's role is the fact that its short term energy output waxes and wanes every 11-12 years, on account of an accumulation of sunspots. With only 40 years of reliable satellite measurements, it is difficult to deduce a trend in solar variations.*   The present solar cycle, as it is called, reached maximum in the middle of 2000 and achieved a second peak in 2002. It is now ramping down toward a solar minimum that arrived in about 2006.

Since the warming trend sharply increased after 2000 it indicates that solar activity played a very minor role in global warming.

*   It has been suggested that the gravitational pull of Jupiter which revolves about the sun in 11.86 years could possibly influence solar radiation in a 11-12 year cycle. Other planets are too small or too remote to make much difference. The only other planet with a large mass is Saturn but it is twice the distance from the sun and since gravitation decreases with the square distance its influence is more than 6-7 times smaller than that of Jupiter.