“Thus, the observed global warming on the Earth is not caused by human-induced greenhouse gases emission, but mostly by unusually high intensity of the solar radiation during the whole passed century. The coming decrease of global temperature will take place even if the anthropogenic CO2 emission will reach record high levels in the future.
The interesting fact is that in XX century global warming took place on Mars as well as on the Earth. This global warming has been caused by considerable and prolonged increase in TSI in XX century. NASA researches were keeping a track of changes on the surface of our neighbour planet — Mars over the period from 1999 to 2005 and they have discovered a gradual melting of ice on its south pole during three Martian years and a simultaneous global warming on Mars, without, of course any participation of Martians and greenhouse effect caused by them. The same simultaneous global warming as on Mars and on the Earth have also been observed on the Jupiter, Triton (a satellite of Neptune), Pluto and several other planets of the solar system. These warmings can only be consequence of the same and only factor ― a prolonged and unusually high value of the TSI during almost whole XX century. The simultaneous global warmings on the Earth, Mars and in virtually whole solar system are the phenomena of the natural solar origin and are caused by natural ― astronomic reasons and not by industrial activity of the humans. “

http://www.gao.spb.ru/english/astrometr/index1_eng.html