An Astronomer's View of Climate Change
  This paper describes some of the astronomical effects that could be important for understanding the ice ages, historic climate changes and the recent temperature increase. These include changes in the sun's luminosity, periodic changes in the earth's orbital parameters, the sun's orbit around our galaxy, the variability of solar activity and the anticorrelation of cosmic ray flux with that activity. Finally recent trends in solar activity and global temperatures are compared with the predictions of climate models. 
Donald C. Morton
physics.ao-ph